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  • Theoretical, Physical and Computational Chemistry  (699)
  • Inorganic Chemistry  (608)
  • 1995-1999  (1,307)
  • 1990-1994
  • 1950-1954
  • 1997  (1,307)
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  • 1995-1999  (1,307)
  • 1990-1994
  • 1950-1954
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  • 1
    Electronic Resource
    Electronic Resource
    Symmetric group approach to relativistic CI. I. General formalism (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 1-10 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: General formulas for matrix elements of spin-dependent operators in a basis of spin-adapted antisymmetrized products of orthonormal orbitals are derived. The resulting formalism may be applied to construction of the Hamiltonian matrices both for Pauli and for projected no-pair relativistic configuration interaction methods. From a formal point of view, it is a generalization of the symmetric group approach to the CI method for the case of spin-dependent Hamiltonians. © 1997 John Wiley & Sons, Inc.
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  • 2
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    Symmetric group approach to relativistic CI. II. Reduction of matrices in the spin space (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 11-20 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An algorithm for the evaluation of matrix representations of products of permutation operators and of one- and two-electron spin-dependent operators in a spin-adapted basis of the N-electron spin space is presented. In particular, the case of the basis functions in which p' electrons are described by products of singlet-coupled pairs is considered in detail. The N-electron spin integrals are, in this case, reduced explicitly to the (N - p') electron ones. © 1997 John Wiley & Sons, Inc.
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  • 3
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    Symmetric group approach to relativistic CI. III. Matrix elements for spin-dependent operators (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 21-34 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Matrix element formulas for spin-dependent operators in a basis of spin-adapted antisymmetrized products of orthonormal orbitals (configuration-state functions) are presented. The coefficients of one- and two-electron integrals depend only on the form of the spin-dependence of the operator and on the mutual arrangement of the orbitals which are singly occupied in the pertinent pair of the configuration-state functions. The formulas are useful in implementations of relativistic two-component CI approaches, such as the Pauli CI and projected no-pair CI method. They may be readily used within existing nonrelativistic SGA - CI codes. As examples of applications of the new formulae, spin-own-orbit and scalar spin - spin matrix elements were derived. © 1997 John Wiley & Sons, Inc.
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  • 4
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    Using full-CI algorithms in Bethe-Goldstone-type expansions of the correlation energy (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 35-43 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the early 1960s, Nesbet proposed to develop correlation energy in terms of two-, three-, four-, etc., electron contributions. This expansion was, in principle, applicable to a large number of electrons without a size-extensivity error. The now available full-CI algorithms may be used to obtain those expansions in terms of either occupied spin - orbitals or, more efficiently, in terms of sets of occupied or virtual molecular orbitals. Tests on the NH3 molecule with a DZP basis-set problem show the slow convergence of this approach. © 1997 John Wiley & Sons, Inc.
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  • 5
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    Unexpected CASSCF bistability phenomenon (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 45-54 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: One exhibits a problem in which two strongly nonorthogonal complete active-space self-consistent field (CASSCF) solutions are obtained. The problem concerns a molecular frame which presents two stable geometries at the CASSCF level, quinoidal and diradical forms, in disagreement with experiment which indicates a unique minimum corresponding to an intermediate geometry. Those two stable solutions are obtained in a significant domain of intermediate geometries and are related with the CASSCF wave functions of the two stable structures. Obtaining a reliable potential surface starting from CASSCF solutions (even from larger CAS) appears as a very difficult task. © 1997 John Wiley & Sons, Inc.
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  • 6
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    Traces of spin-adapted reduced density matrices (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 55-61 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The traces of the p-order reduced density matrices (p-RDM) split into independent contributions associated to the subsets of p-electron eigenstates of the Ŝ2 and Ŝz operators. Here, we report the partial traces for the blocks of the low-order RDMs corresponding to pure spin states of an N-electron system. A systematic method for calculating those of higher order RDMs is described and some useful relations are also given. All these relations which must be fulfilled independently by a RDM can be considered as N- and S-representability conditions © 1997 John Wiley & Sons, Inc.
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  • 7
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    Average energy of an N-electron system in a finite-dimensional and spin-adapted model space (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 63-65 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An expression for the average energy of an N-electron system in a finite-dimensional, antisymmetric, and spin-adapted model space (as, e.g., a full-configuration interaction space) is derived using elementary properties of the Hamiltonian in the Fock space. © 1997 John Wiley & Sons, Inc.
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  • 8
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    Nonempirical wave functions for very large molecules. II. The PRDDO/M/FCP method (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 67-76 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A variation of the frozen-core potential (FCP) method is developed and implemented within the modified version of the method of partial retention of diatomic differential overlap (PRDDO/M). The explicit treatment of core electrons is replaced with a potential based on the actual core-valence integrals rather than upon an arbitrary model potential. The core-valence orthogonality requirement is replaced by an energy shift operator. PRDDO/M/FCP calculations exhibit good agreement with ab initio calculations with the same basis set, while reducing the computational cost significantly. © 1997 John Wiley & Sons, Inc.
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  • 9
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    Maximum-entropy analysis of momentum densities in diatomic molecules (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 77-83 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The one-particle density in momentum space γ(p) is studied for diatomic molecules by using the maximum-entropy technique. The knowledge of one or more momentum expectation values 〈pn〉 provides approximations on the density γ(p) for any value of the momentum, which are convergent when increasing the number of known moments. Other unknown expectation values are estimated in terms of the constructed maximum-entropy densities. A numerical study of the quality of the approximations is carried out by means of experimental and theoretical data for the momentum expectation values involved. Experimental errors are also taken into account to have an idea of the sensibility of the results to the information from which they are obtained. © 1997 John Wiley & Sons, Inc.
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  • 10
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    Electron affinities of metals computed by density functional theory and ab initio methods (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 93-100 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An extensive computational study of the meal electron affinity was performed using the ab initio and density functional theory (DFT) methods. HF, MP2, MP3, MP4, QCISD, and QCISD(T) was used as computational methods, while the hybrid, local, and nonlocal DFT methods with the LYP, P86, PW91, and VWN correlation functionals were used. Two basis sets, one small and applicable to almost all metals (LanL2DZ) and one large [6-311 + + G(3df, 3 pd)] used only for small metals, were employed. The computed results were compared with the experimental data and the capabilities of the DFT methods to perform this study were discussed. © 1997 John Wiley & Sons, Inc.
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  • 11
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    The relative performance of the local density approximation and gradient-corrected density functional theory for computing metal-ligand distances in Werner-type and organometallic complexes (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 85-91 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Optimized metal-ligand (M-L) bond lengths for 17 classical Werner-type transition-metal complexes were calculated using the local density approximation (LDA) and a gradient-corrected (GC) extension. GCs lengthen the bonds by between 0.02 and 0.09 Å relative to the LDA results. The latter range from 0.02 Å shorter than observed to 0.05 Å longer, while the GC data range from exact agreement with experiment to some 0.12 Å too long. The LDA rms deviation is 0.025 Å compared to the GC error of 0.070 Å. In contrast, data from the literature for organometallic species show that the LDA gives systematically too short M-L distances and GCs lead to a better agreement with experiment. The relative performance of LDA and GC functionals reflects the qualitatively different chemistries of organometallic and Werner-type complexes. The magnitude of the GC bond-length expansion for the latter correlates with the ionicity of the M-L interaction. © 1997 John Wiley & Sons, Inc.
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  • 12
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    CFPHGLF calculation of 3S excited states for heliumlike three-body systems (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 101-105 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The correlation-function potential-harmonic and generalized Laguerre function method (CFPHGLF) proposed recently by us is used to directly solve the Schrödinger equations of low-lying triplet states n3S (n = 2-5) for a set of heliumlike systems, including He, Li+, and Be2+. The eigenenergies converge fast and steadily with potential harmonics (PH) and generalized Laguerre functions (GLF). With 10 PH, the percentage errors in the convergent ionization energies for 23S, 33S, 43S, and 53S states of the helium atom are 0.548, 0.291, 0.247, and 0.265% relative to the Hylleraas CI variational values. Somewhat better precision is achieved for Li+ and Be2+ systems. © 1997 John Wiley & Sons, Inc.
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  • 13
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    Theoretical studies on the structures and electronic spectra of C70CH2 (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 815-822 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Intermediate neglect of differential overlap (INDO) calculations were used to study the structure of C70CH2. It was found that the CH2 group is mainly added to the CI(SINGLE BOND)CII (CI represents the first kind of carbon atom and so on) or the CIII(SINGLE BOND)CIII bond in C70 and a cyclopropane feature with Cs symmetry is formed in the structure, which is in agreement with Smith et al.'s experiment. The electronic spectra of eight isomers of C70CH2 were calculated based on the optimized geometries. It was shown that the UV/vis spectra of C70CH2 and C70 resemble each other in many ways with the exception of the absorptions beyond 500 nm. The red-shift of the absorptions and NMR spectra of C70CH2 are discussed. © 1997 John Wiley & Sons, Inc.
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  • 14
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    Peptide models. XIV. Ab initio study on the role of side-chain backbone interaction stabilizing the building unit of right- and left-handed helices in peptides and proteins (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 797-814 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Previous ab initio computations revealed that the conformational building unit of the right-handed helix (φ ≈ -54°, ψ ≈ -45°) is not an energy minimum on two-dimensional-type Ramachandran potential energy surfaces (E = E{φ, ψ}). Theoretical investigations were performed on several single-amino-acid diamides such as For-Gly-NH2, For-L-Ala-NH2, Ac-L-Ala-NHMe, and For-L-Val-NH2 containing amino acid residues (e.g., Ala) which can often be found in helices as shown by X-ray data analysis of globular proteins. The current ab initio [self-consistent field (SCF)] results (based on four different basis sets [3-21G, 4-21G, 4-21G*, and 6-31G*]) presented point toward an intrinsic (i.e., non-environmental-assisted) stability of the right-handed helical subconformation of a simple amino acid diamide if the residue contains a polar side chain. Such is the case for a serine derivative when its (SINGLE BOND)CH2OH side chain is favorably oriented. For the For-L-Ser-NH2 model compound two slightly different right-handed helical backbone conformations were determined. Depending on the relative orientation of the side chain, the conformational monomer of the 310 helix (a sharper helical structure with an [i, i + 3]-type H-bond network) as well as the building block of the “standard” α-helix (the regular helical structure with an [i, i + 4]-type H-bond network) were determined computationally by geometry optimization. © 1997 John Wiley & Sons, Inc.
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  • 15
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    Cloppa RPA-AM1 analysis of the anisotropy of NMR 1J(XY) coupling tensors in Me3XY compounds (X = 13C, 29Si, 119Sn, 207Pb; Y = 19F, 35Cl) (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 823-833 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this work, the CLOPPA approach is extended to allow the bond-contribution analysis of the anisotropic part, ΔJ, of the indirect nuclear spin-spin coupling tensor, J. As an example this method is applied to study the role played by the X-Y bond, its antibonding orbital, and the Y lone pairs in determining the Fermi contact-spin dipolar cross contribution to Δ1J(XY) in compounds of type Me3X(SINGLE BOND)Y (X = C, Si, Sn, Pb; Y = F, Cl). That contribution is found to be the main one, except for × = Pb, in this series of compounds. Calculations are carried out using semiempirical AM1 ground-state wave functions. © 1997 John Wiley & Sons, Inc.
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  • 16
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    Density-gradient analysis for density functional theory: Application to atoms (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 835-845 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We present an analysis of local or semilocal density functionals for the exchange-correlation energy by decomposing them into their gradients rs (local Seitz radius), ζ (relative spin polarization), and s (reduced density gradient). We explain the numerical method pertaining to this kind of analysis and present results for a few atoms and ions. The atomic shell structure is prominent, and only the ranges 0 〈 rs 〈 10 and 0 〈 s 〈 3 are important. The low-density and large-gradient domains, where the approximations for the exchange-correlation energy are least trustworthy, have very little weight. © 1997 John Wiley & Sons, Inc.
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  • 17
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    The effect of an electric field on the vibrational frequency of CN (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 859-863 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ab initio calculations are used to compute the change in the vibrational frequency of CN with an applied electric field aligned parallel to the bond axis. The effect of the field on the CN- vibrational frequency is of the same magnitude as for CN, but in the opposite direction. These results are compared to previous results for CO. © 1997 John Wiley & Sons, Inc.
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  • 18
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    Conductivity in polyacetylene. IV. Ab initio calculations for a two-site model for electron transfer between allyl anion and allyl (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 847-857 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Electron exchange between allyl molecules is studied using quantum chemical ab initio methods in order to model interchain electron transfer (ET) in polyacetylene. The reaction path, reorganization energy for ET (λ), and the electronic factor (Δ) are calculated using the UMP2, CASSCF, CASPT2, and CASSI methods. Changes in bond lengths are very small and their contribution to the internal reorganization energy almost negligible. Only changes in the bond angle leave significant contributions to the reorganization energy. The calculated potential energy surfaces can be represented as interacting parabolic-well potentials only in the case of CASSI. The UMP2, CASSCF, and CASPT2 methods give the localization of the electron even in the symmetric case and incorrect energy surfaces, with a cusp at the symmetry point. The electronic factor Δ is calculated using the two different methods, Koopmans' theorem and CASSI, with the same basis set. They are quantitatively very close for all intermolecular distances under study. However, Δ is sensitive to the basis set and cannot be calculated accurately in the present case. © 1997 John Wiley & Sons, Inc.
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  • 19
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    Theoretical investigation of the rates of electron transfer processes Q-I + QII → QI + Q-II and Q-I + Q-II → QI + Q2-II in photosynthesis (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 865-879 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A theoretical investigation on the rates of electron-transfer processes Q-I + QII → Q-I + Q-II and Q-I + Q-II → QI + Q2-II was carried out by using the Marcus theory of long-range electron transfer in solution. The molecular reorganizational parameter λ, the free-energy change ΔG0 for the overall reaction, and the electronic matrix element HDA for these two processes were calculated from the INDO-optimized geometries of molecules QI, QII, and histidine. QI and QII are plastoquinones (PQ) which are hydrogen-bonded to a histidine each, and the two histidines may or may not be coordinated to a Fe2+ ion. The plastoquinone representing QI is additionally flanked by two peptide fragments. Each of the species (Pep)2QI · His and His · QII has been considered to be immersed in a dielectric continuum that represents the surrounding molecules and protein folds. INDO calculations confirm the standard reduction potential for the first process (calculated 0.127 V; observed 0.13 V) and predict a midpoint potential of 0.174 V for the second process at 300 K at pH 7 (experimental value remains uncertain but is known to be close to 0.13 V). The plastoquinone fragment carries almost all the net charge (about 95.7%) in [PQ · His]- and the net charge in [PQH · His]-. The electron is transferred effectively from the plastoquinone part of [(Pep)2QI · His]- to the plastoquinone moiety of QII · His in the first step and to the plastoquinone fragment of HisH+ · Q-II in the second step. Therefore, we made use of the formula for the rate of through-space electron transfer from QI to QII (and to Q-II). The plastoquinones are, of course, electronically coupled to histidines, and the transfer is, in reality, through the molecular bridge consisting of histidines and also Fe2+. The through-bridge effect is inherent in our calculation of ΔG0, HDA, and the reorganization parameter λ. We investigated the correlation between half-times for the transfer and (D-1op- D-1s), where Dop and Ds are, respectively, optical and static dielectric constants of the condensed phase in the vicinity of the plastoquinones. We found that with reasonable values of Dop (2.6) and Ds (8.5) the experimental rates are adequately explained in terms of transfers from the plastoquinone moiety of QI to that of QII. The t1/2 values calculated for the two processes are 247 and 472 μs in the absence of Fe2+ and 134 and 181 μs in the presence of Fe2+. These are in good agreement with the observed values which are ≈ 100 and ≈ 200 μs when Fe2+ is present in the matrix and which are known to be almost twice as large when the Fe2+ is evicted from the matrix. The present work also shows that the Marcus-Hush theory of long-range electron transfers can be successfully applied to the investigation of processes occurring in a semirigid condensed phase like the thylakoid membrane region. © 1997 John Wiley & Sons, Inc.
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    Design of an exchange functional with correct asymptotics (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 891-898 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Knowledge of asymptotic conditions on exchange allows for a better design of exchange energy expressions in density functional theory. By working inside an exchange-only framework, the fulfillment of such conditions by some of the most widely used exchange functionals is discussed. In turn, we propose a model expression which partially meets the energetics and asymptotics of both the exchange energy density and potential. Improvement upon the local spin density approximation without the use of generalized gradient corrections is also presented. Hartree-Fock orbitals are employed to build electron densities. © 1997 John Wiley & Sons, Inc.
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    Addendum to construction of linearly independent relativistic symmetry orbitals for finite double-point groups including time-reversal symmetry (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 929-933 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In a previous article [J. Meyer, Int. J. Quantum Chem. 33, 445 (1988)], the formalism for the construction of linearly independent relativistic symmetry-adapted molecular basis functions under consideration of time-reversal symmetry was published. We present here an addition and correction of the application of time reversal on the construction. This new theory is now applicable to all double-point groups, including the icosahedral groups not considered so far. © 1997 John Wiley & Sons, Inc.
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    Correlation entropy of the H2 molecule (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 935-941 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Correlation of a quantum many-body state makes the one-particle density matrix nonidempotent. Therefore, the Shannon entropy of the natural occupation numbers measures the correlation strength on the one-particle level. Here, it is shown how this general idea of a correlation entropy must be adapted for two-electron systems in view of conservation laws which mix Slater determinants even in the noninteracting limit. Results are presented for the correlation entropy s of H2 as a function of the nucleus-nucleus separation R. In the ground state, the entropy of the spatial factor of the wave function maximizes 1.7 bohr beyond the Coulson-Fischer separation. The role of the correlation entropy in density functional theory is also discussed. © 1997 John Wiley & Sons, Inc.
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  • 23
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    Optimized Gaussian basis sets for use with relativistic effective (core) potentials: K, Ca, Ga—Kr (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 943-952 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Correlation-consistent valence basis sets were developed for the third-row main block elements (K, Ca, Ga - Kr) for use with relativistic effective core potentials. These basis sets are somewhat larger than double-zeta in size, with polarization functions, and are balanced for use in both Hartree-Fock and correlation calculations. Spin-orbit splittings for atoms and molecules are calculated and compared to experiment. These calculations use the approximate spin-orbit operator from the relativistic effective core potentials. The use of these results in the calculation of accurate thermochemical data is discussed. © 1997 John Wiley & Sons, Inc. This article is a US Government work and, as such, is in the public domain in the United States of America.
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    An ab initio study of the structure, dissociation energy, and heat of formation of Na2S (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 953-957 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The equilibrium geometries and fundamental frequencies of Na2S are calculated at HF, MP2(FC, FU), and MP3 with the 6-31G(d) basis set and at HF and MP2(FC, FU) with the 6-31G(d) basis set, respectively. The total energy at MP2(FU)/6-31G(d)-optimized geometry is computed at MP4 with 6-311G(d, p), 6-311 + G(d, p), and 6-311G(2df, p), at QCISD(T)/6-311G(d, p), and at MP2/6-311G(3df, 2p) levels, respectively. The dissociation energy, the atomization energy, and the heat of formation for Na2S are evaluated using the G1 and G2 models. The calculated results indicated that Na2S in its ground state was a bent structure (C2v). Electron correlation corrections on the bending angle are very significant. The equilibrium geometrical parameters are Re(Na-S) = 2.45 Å and ∠Na-S-Na = 111.13° at the MP2(FU)/6-31G(d) level. The theoretically estimated dissociation energy, total atomization energy, and heat of formation are 67.07, 117.55, and 0.35 kcal mol-1, respectively, at 298.15 K. © 1997 John Wiley & Sons, Inc.
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    Theoretical studies on local anesthetics: Procaine, lidocaine, tetracaine, bupivacaine, and dibucaine - neutral and monoprotonated (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 959-980 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The molecular basis of the pharmacological action of tertiary amine local anesthetics (LA) is still unclear. However, there is experimental evidence that the LA penetrates into the axon as a neutral form and acts in the charged form from the intracellular phase. In this work we report quantum chemical semiempirical results for the neutral and monoprotonated forms of procaine, lidocaine, tetracaine, bupivacaine, and dibucaine. All geometries have been fully optimized with the AM1 Hamiltonian. Solvent effects were included at the self-consistent reaction field (SCRF) approximation. We have found that the most stable conformers of positively charged LA agents are all characterized by intramolecular H-bond formation involving the protonated amine groups. INDO/S-CIS calculations have revealed that the gas-phase absorption spectra of LAs result from the superposition of the spectra of the ring π system and the carbonyl, in a large extent perturbed by intramolecular charge transfer (CT). For all studied LAs, the benzene B2u bands are very weak and the benzene B1u bands gain intensity due to symmetry breaking. Formation of intramolecular H bond strongly affects the carbonyl CT bands. On the other hand, the spectrum of dibucaine is dominated by the quinoline π system. © 1997 John Wiley & Sons, Inc.
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    Structure and energy of the positively ionized water clusters (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 981-990 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Geometry optimization of small (H2O)n+ clusters (n ≤ 4) at the UHF/4-31 + + G** level indicates that the cations consist of two fragments: the OH radical and the H2n-1 O+n-1 ion. The latter can be considered as a thermodynamically stable combination of a distorted H3O+ ion and (n-2) H2O molecules. The H bond between the fragments becomes weaker with increasing cluster size. Extrapolation of the adiabatic ionization potentials calculated for the (H2O)n oligomers (n ≤ 4) at the MP2 level to an infinite cluster size provides the value of approximately 8.7 eV, which can be presumably necessary for the ionization of liquid water in a vacuum. © 1997 John Wiley & Sons, Inc.
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    Calculations of the structure and electronic properties of extended polar hydrocarbons (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 991-996 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The structure and nonlinear optical potential of a series of polar unsaturated hydrocarbons containing the electron-donating heptafulvene ring and electron-attracting pentafulvene ring have been explored in terms of their first hyperpolarizabilities using a semiempirical sum-over-states and time-dependent coupled Hartree-Fock approach. Both methods predict that the hyperpolarizabilities of these simple hydrocarbons are substantial and exceed those found for many extended conventional donor-acceptor systems. © 1997 John Wiley & Sons, Inc.
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    Time-evolution operator for a forced parametric oscillator (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 62 (1997), S. 125-135 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We apply an algebraic technique to describe the evolution of a parametric harmonic oscillator forced by a constant quartic potential. As the first step, we make use of iterative Bogolubov transformations (IBT) to incorporate information from the anharmonic part of the interaction in a nonperturbative form, yielding a unitary time-evolution operator. Later on, we make use of first-order perturbation theory to deal with that part of the interaction which was not incorporated previously. We show numerically that the resulting time-evolution operator is closer to unitarity than is the one obtained if no IBT is applied. The quantum fluctuations of position and momentum are evaluated for “the ground” state. Squeezing and correlation effects are observed. © 1997 John Wiley & Sons, Inc.
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    Single-reference CCSD approach employing three- and four-body CAS SCF corrections: A preliminary study of a simple model (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 62 (1997), S. 137-151 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The idea of correcting the single-reference coupled cluster (CC) method truncated at the pair cluster level (CCSD) by means of three- and four-body corrections coming from some external source [J. Paldus, J. Čížek, and M. Takahashi, Phys. Rev. A 30, 2193 (1984); J. Paldus and J. Planelles, Theor. Chim. Acta 89, 13 (1994)] is explored at the ab initio level using the CAS SCF wave functions as a source of the triply and quadruply excited cluster amplitudes. The method (referred to as CCSD-CAS) is applied to three simple systems based on minimum basis set and double-zeta models of the BH molecule, in which we continuously vary, respectively, (i) the two electron repulsion, (ii) the electronic charge, and (iii) the internuclear separation in order to explore the performance of the method in quasi-degenerate situations. Both the energies and the higher than pair cluster amplitudes are compared with the corresponding exact full configuration interaction (FCI) results. The relative importance of the three- and four-body cluster components is also examined. In all cases considered, the CCSD-CAS method provides the best result. © 1997 John Wiley & Sons, Inc.
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    On the restricted step method coupled with the augmented Hessian for the search of stationary points of any continuous function (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 62 (1997), S. 153-165 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In any optimization using the augmented Hessian technique, the step is not restricted to any length. Since the restriction of the step at each iteration is very important in order to achieve good convergence, we present a coupled method such that the augmented Hessian automatically gives both the adequate length of the step and the correct Hessian structure. The method is showed for the minima and saddle points of any order. © 1997 John Wiley & Sons, Inc.
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    Statistical electron densities (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 85-93 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: It is known that in numerous interesting systems one-electron states appear with a multifractal internal structure. Physical intuition suggests, however, that electron densities should be smooth both at atomic distances and close to the macroscopic limit. Multifractal behavior is expected at intermediate length scales, with observable nontrivial statistical properties in considerably, but far from macroscopically sized clusters. We have demonstrated that differences of generalized Rényi entropies serve as relevant quantities for the global characterization of the statistical nature of such electron densities. Asymptotic expansion formulas are elaborated for these values as functions of the length scale of observation. The transition from deterministic electron densities to statistical ones along various lengths of resolution is traced both theoretically and by numerical calculations.    © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 85-93, 1997
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    Adiabaticity and gauge transformations for an oscillator coupled to a single-mode field (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 111-119 
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    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The components of the Floquet wave function of an oscillator in various representations are correlated. The transformation from length to velocity gauge can be viewed as a change from a diabatic to an adiabatic representation in the field variable. This is shown in three different ways.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 111-119, 1997
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    The optimized effective potential method of density functional theory: Applications to atomic and molecular systems (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 95-110 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Using the optimized effective potential method in conjunction with the semianalytical approximation due to Krieger, Li, and Iafrate, we performed fully self-consistent exact exchange-only density functional calculations for diatomic molecules with a fully numerical basis-set-free molecular code. The results are very similar to the ones obtained with the Hartree-Fock approach. Furthermore, we present results for ground states of positive atomic ions including correlation contributions in the approximation of Colle and Salvetti. It is found that the scheme performs significantly better than do conventional Kohn-Sham calculations.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 95-110, 1997
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    Energies of dipole-bound anionic states (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 183-191 
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    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Dipole-bound anionic states of CH3CN, C3H2, and (HF)2 were studied using highly correlated electronic structure methods and extended one-electron basis sets. The electron detachment energies were calculated using the coupled cluster method with single, double, and noniterative triple excitations. Geometrical relaxation of the molecular framework upon electron attachment and the difference in the harmonic zero-point vibrational energies between the neutral and the dipole-bound anionic species were calculated at the MP2 level of theory. We demonstrate that the dispersion interaction between the loosely bound electron and the electrons of the neutral molecule is an important component of the electron binding energy, comparable in magnitude to the electrostatic electron-dipole stabilization. The geometrical relaxation upon electron attachment and the change in the zero-point vibrational energy is important for the weakly bound HF dimer. The predicted values of the vertical electron detachment energies for the dipole bound states of CH3CN and C3H2 of 112 and 188 cm-1, respectively, are in excellent agreement with the recent experimental results of 93 and 171±50 cm-1, respectively. For (HF)2-, the predicted value of adiabatic electron detachment energy is 396 cm-1, whereas the experimental vertical detachment energy is 508±24 cm-1. The possibility of formation of the neutral dimer in an excited vibrational state is considered.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 183-191, 1997
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    Accurate density-functional calculations on large systems (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 193-203 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Efforts to compute accurate all-electron density-functional energies for large molecules and clusters using Gaussian basis sets are reviewed and their use in fullerene science described. The foundation of this effort, variational fitting, is described first. When discovered experimentally, C60 was naturally assumed to be particularly stable, but local-density-functional calculations showed that C60 is quite unstable relative to the higher fullerenes and graphene (a single sheet of graphite). In addition to raising questions about the relative abundance of the various fullerenes, this work conflicted with the then state-of-the-art density-functional calculations on crystalline graphene. Now high accuracy molecular and band structure calculations are in fairly good agreement with each other and experiment. These calculations clearly demonstrate that each of the 12 pentagons, which are necessary to close a fullerene, is best viewed as a rather high-energy, more than 2 eV, defect in a graphene sheet. The effect of the heptagon, the second most common defect in fullerene materials, is described. Most recently, we have developed accurate, variational gradient-corrected forces for use in geometry optimization of clusters and in molecular-dynamics simulations of friction. The gradient-corrected optimized geometry of C60 is given.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 193-203, 1997
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    Density-functional investigation of some decomposition routes of methyl nitrate (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 205-210 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two density-functional methods, B3/LYP/6-31+G(d) and B3/PW91/6-31G(d, p) have been used to investigate some possible decomposition pathways for methyl nitrate. Two likely ones were found to be (a) loss of NO2, followed by eventual rearrangement to H2C(SINGLE BOND)OH, and (b) formation of H2C(DOUBLE BOND)O and HONO. The initial energy requirement for each process is about 40 kcal/mol, and the second is exothermic, ΔH=-16 kcal/mol of H3C(SINGLE BOND)ONO2. The B3/LYP procedure is found to underestimate the H3CO(SINGLE BOND)NO2 and H3C(SINGLE BOND)ONO2 dissociation energies by about 6 kcal/mol.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 205-210, 1997
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    The role of the Jahn-Teller distortions on the structural, binding, and magnetic properties of small Fen clusters, n≤7 (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 223-230 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Small clusters of iron atoms, up to heptamers, were studied by density functional theory. The calculations performed were all-electron and both local and gradient-dependent potentials were used. Most of the symmetric or compact structures show degenerate electronic states which are stabilized, through Jahn-Teller distortions, in lower symmetry or more open geometries. As the cluster size increases, the coordination numbers increase, the metal-metal bond strengths are reduced, and the equilibrium bond lengths are enlarged. This behavior accounts for the occurrence of high magnetic moments on the atomic sites, which are coupled ferromagnetically.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 223-230, 1997
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    Studies of chemical hardness and chemical potential on isomers and hardness profiles of hydrogen-bonded systems (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 231-242 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the present investigation, chemical hardness and electronic chemical potential for isomers of different molecules were studied by taking into account the principle of maximum hardness. Different isomers of the molecules, XC(O)OX (X=F, Cl), C2H3NO, C2H2, and HCNC, were considered for the above investigation. In most of the cases, the chemical hardness was found to be a good indicator for predicting the most stable isomer and not the chemical potential. The hardness profiles of different configurations of the interacting systems, HF(DOTTED BOND)HCN, HF(DOTTED BOND)HCl, and CH3OH(DOTTED BOND)H2O hydrogen-bonded complexes, were studied. The extrema of the hardness profiles does not coincide well with the energy, but in some cases, the hardness profile follows the interaction path. The higher hardness-higher stability concept among different configurations of the hydrogen-bonded complexes are discussed.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 231-242, 1997
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    Ionized van der Waals systems: Structure and interactions (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 211-222 
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    ISSN: 0020-7608
    Keywords: quantum chemistry ; weak interactions ; cationic van der Waals complexes ; cluster cations ; potential energy surfaces ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ions of molecular complexes with internal interactions partly of van der Waals type differ significantly from their neutral parent species in binding, structure, and dynamics. Information about such systems is still rather scarce, both experimentally and theoretically. The article discusses some aspects of the present knowledge concerning cationic dimers and trimers of the type RgnM+ with Rg denoting a rare-gas atom, and M, either a (diatomic) molecule or a rare-gas atom, in comparison with the neutral counterparts. In some more detail, potential energy surfaces (PESs) for the six lowest electronic states of ArHCl+ are reported, as obtained from multireference CI calculations with an extended Gaussian AO basis set. From the PESs, structural, energetical, and dynamical features are derived. For the cationic argon trimer Ar3+ in the electronic ground state, a detailed analysis of the PES, the mode couplings, and the classical internal dynamics is carried out, leading to a consistent picture of a floppy molecular aggregate with rapid energy exchange between internal degrees of freedom and early onset of classical chaos with increasing energy.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 211-222, 1997
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    An LDA calculation of the conformation and electronic structure of polytetrafluoroethylene (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 243-246 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A density functional calculation of the structural and electronic properties of polytetrafluoroethylene systems with several different dihedral angles is presented using two different local density approximations, the Gáspár-Kohn-Sham and the Perdew-Zunger. All the geometrical parameters were optimized simultaneously for the stable conformation. The torsional potential curve shows an absolute minimum at the dihedral angle of 163.7°, corresponding to a slightly deformed planar zigzag conformation. Other two distinct local minima for the quasi-stable helical conformation are found at the gauche form. The calculated valence and conduction bands are discussed and compared with other theoretical calculations and experiment.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 243-246, 1997
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    Computation of geometries and frequencies of singlet and triplet nitromethane with density functional theory using Gaussian-type orbitals (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 263-269 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The results of computational studies of the structures, energies, dipole moments, and infrared spectra for singlet and triplet nitromethane are presented. Five different hybrid (B HandH, BHandHLYP, B3LYP, B3P86 and B3PW91), local (SVWN), and nonlocal (BLYP) density functional theory (DFT) methods were used in this study with various sizes of a Gaussian-type basis set. The obtained results were compared to Hartree-Fock (HF), second-order Møller-Plesset (MP2), and multiconfiguration self-consistent-field (MCSCF) ab initio calculations, as well as to the experimental results. The suitability of DFT methods to correctly reproduce experimental results is discussed.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 263-269, 1997
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    Computation of some ionization potentials for second-row elements by ab initio and density functional theory methods (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 255-261 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Four ionization potentials of elements from the second row of the periodic table were computed with ab initio (HF, MP2, MP3, MP4, QCISD, G1, G2, and G2MP2) and density functional theory (DFT) (B3LY, B3P86, B3PW91, XALPHA, HFS, HFB, BLYP, BP86, BPW91, BVWN, XAPLY, XAP86, XAPW91, XAVWN, SLYP, SP86, SPW91 and SVWN) methods. In all of the calculations, a large 6-311++G(3df, 3pd) Gaussian-type basis set was used. The computed values were compared to experimental results, and the suitability of these ab initio and DTF methods for computing atomic ionization potentials was discussed. It was found that G2 will produce ionization potentials that are indistinguishable from the experimental values. Hybrid B3LYP and nonlocal BLYP will generate very good ionization potentials. For larger atoms, SLYP and SPW91 will compute ionization potentials that are of G2 quality.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 255-261, 1997
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    Comparative AM1 study of the electronic structure of etiocholanes (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 249-254 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Etiocholanes are metabolites of androstenedione (4-androsten-3,17-dione) and testosterone (17β-hydroxy-4-androsten-3-one). These compounds are produced by the action of 5-reductases which break the π double bond of the androstenes at C4 and C5. The most important etiocholanes are 5β-androstanedione (etiocholanedione), 3α-hydroxy-5β-androstan-17-one (etiocholanolone), 3β-hydroxy-5β-androstan-17-one (epietiocholanolone), and 17β-hydroxy-5β-androstan-3-one (5β-dihydrotestosterone; 5βDHT). Among their most important biological effects are depression of the central nervous system, relaxation of smooth muscle, and stimulation of sexual behavior. The intent of the present study is a determination of the effects of carbonyl and hydroxyl groups at C3 and C17 on the electronic structure of these androgens, in an attempt to gain some insight into their biological action. All calculations were of the semiempirical AM1 type. The decrease of enthalpy caused by an hydroxyl group was found to be twice that of a carbonyl group. The effect of two groups was found to be additive. Carbonyl groups on the other hand led to an increase of dipole moment and of the electrostatic charges on neighboring carbons that were higher than those produced by hydroxyl groups. Carbonyl groups at C17 pushed the highest occupied molecular orbital (HOMO) to higher energy whereas a carbonyl at C3 had little or no effect. However, in mono and di-keto structures, both HOMO and lowest unoccupied molecular orbital (LUMO) were located as expected closer to the carbonyl group. Etiocholanedione, a diketo structure, showed degeneracy of frontier orbitals with its related HOMO-1 and LUMO+1. Structures with mono-hydroxyl or di-hydroxyl functional groups showed the lowest HOMO values; the highest LUMO values and quasi degeneracy of HOMO-1 and LUMO+1. The HOMO and LUMO of etiocholane and for the mono and di-hydroxyl structures were observed diffused throughout the molecules in a “sausagelike” or “ribbonlike” fashion. These results might explain some metabolic steps. Likewise, the difference of intermolecular forces, i.e., dipole moments and charges displayed by the carbonyl and hydroxyl groups, might help to elucidate some biological effects.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 249-254, 1997
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    Coupling-constant dependence of atomization energies (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 285-295 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The local spin-density (LSD) functional and Perdew-Wang 91 (PW91) generalized gradient approximations to atomization energies of molecules are investigated. We discuss the coupling-constant dependence of the atomization energy and why exchange errors of the functionals are greater than exchange-correlation errors. This fact helps to justify hybrid schemes which mix some exact exchange with density functional approximations for exchange and correlation. It is shown that the biggest errors in the atomization energies occur when there is a strong interaction between different electron pairs, which vanishes upon atomization. We argue that the amount of exchange character of a molecular property, such as the atomization energy, depends on the property itself. We define an exact mixing coefficient b, which measures this exchange character, and show that both LSD and PW91 typically overestimate this quantity. Thus, nonempirical hybrid schemes which approximate this quantity by its LSD or PW91 value typically do not improve the exchange-correlation energy.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 285-295, 1997
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    QR-SCMEH-MO calculations on lanthanide systems. IV. The [SmCp*]4 cluster (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 297-300 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Additional calculations via the quasi-relativistic self-consistent-modified extended Hückel-MO method (QR-SCMEH-MO) were conducted on the model cluster [SmCp*]48+ and the real [SmCp*]4(N2H2)2(N2H3) 4(NH3)2 cluster. It is shown that this is no trivial problem, owing to correlation arising from the electron repulsion among open shells, plus the close proximity of open- and closed-shell configurations. An acceptable result is shown to be sensitive to spin-orbit splitting and electron-pairing interactions.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 297-300, 1997
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    The distribution of polynuclear aromatic hydrocarbons between aquatic plants and sediments (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 271-283 
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    ISSN: 0020-7608
    Keywords: acropetal ; adsorption ; aquatic plants ; polynuclear aromatic hydrocarbons ; sediments ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Saturation phenomena for the uptake of polynuclear aromatic hydrocarbons (PAHs) by rooted aquatic plants were observed in both field and laboratory experiments. From these data, a Langmuir adsorption model was derived and was shown to describe the assimilation of sediment PAHs by aquatic plants at low-sediment PAH concentrations. The low-concentration restrictions were relaxed by using an empirical Freundlich model. This permitted the specification of equilibrium constants, relative rate constants for adsorption and desorption, and saturation levels, and it provided a realistic description of the acropetal mobilization of sediment PAHs by rooted aquatic macrophytes. The growth of aquatic plants was found to be inhibited by sediment PAHs, but at concentrations several orders of magnitude above the corresponding threshold effect levels for aquatic animals. The effects of the acropetal transport of sediment PAHs into the above-soil portions of aquatic plants merits further investigation because of the possibility of an enhanced availability of these carcinogens to associated aquatic food webs. In addition, these results may suggest pathways for bioremediation of the impact of PAHs on associated biota.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 271-283, 1997
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    Geometry optimization of polymers by the elongation method (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 301-323 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Theoretical studies on the electronic and the geometrical structures for various molecules by the molecular orbital or the density functional theory have recently been developed and applied widely under the progress of computer technologies. At present, it is possible to carry out a theoretical investigation on electronic properties for small molecules at the Hartree-Fock and the post-Hartree-Fock levels by the improvement of advanced program packages. However, it is difficult to perform the theoretical calculations on electronic structures for large polymers with the aperiodic sequence of molecular segments, because the theoretical treatment of random systems has not yet been established. We recently proposed the elongation method as a useful theoretical approach to obtain the electronic states of any polymers without the periodic geometry of molecular fragments. In the previous works, the reliability of our treatment has been shown by the application to many polymers under single-point calculations with fixed molecular geometry. Thus, as the next step of our study, an attempt for the geometry optimization of large polymers by the elongation method was made in this work. As the first samples of geometry optimization, the periodic polymers of polyethylene, polyacetylene, and polyglycine were examined. Also, as the second samples, the locally aperiodic polymers of polyacetylene with local defects of positively and negatively charged solitons were tested. Total energies, optimized geometries, and electron densities were checked by those obtained from the conventional molecular orbital method.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 301-323, 1997
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    Molecular orbital approach to the Peierls instability in polyenes and its application to model crystals of charge-transfer complexes (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 325-336 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We have already proposed a convenient method to estimate the magnitude of the Peierls instability in finite one- and two-dimensional (1D and 2D) polyenes from the viewpoint of orbital symmetry [J. Chem. Phys., 103, 9726 (1995)]. This treatment is applied to a model system for charge-transfer complexes, in which the unpaired electron is occupied in a molecule, generating a half-filled energy band by intermolecular interaction. As the first step, a model molecular crystal composed of ethylene anion (or cation) molecules is treated to confirm the applicability of our formulas for 2D polyene. It is clearly shown that molecules in a crystal are structurally distorted to gain the energetic stabilization within the 1D structure, while they are rearranged in a regularly equidistant structure under strong interchain interaction. This treatment would provide insight into the relationship between the crystal structure of charge-transfer complexes and its electronic property.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 325-336, 1997
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    Heterogeneous reactions over fractal surfaces: A multifractal scaling analysis (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 337-350 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Monte Carlo simulations of Eley-Rideal (ER) mechanisms with fixed and varying sticking probabilities, p, as well as a three-step catalytic reaction (TCR) over fractal surfaces were performed to examine the morphological effect on the above-mentioned reactions. The effect of decay and enhancing profiles on the reaction probability distribution (RPD) for the ER reaction as well as effects of a varying probability of reaction steps on the normalized selectivity distribution (NSD) for the three-step reaction were then analyzed by multifractal scaling techniques. For ER with a fixed sticking probability, a small p value tends to yield homogeneous RPD. For ER with a varying sticking probability, the RPD is revealed to be spatially uniform at fast decay and rather concentrated at a faster enhancing rate. For the three-step reaction, a large dimerization/isomerization ratio increases the position distinction among active sites as the adsorption probability equals 1. At a small adsorption probability, the dimerization/isomerization ratio causes no effect on the NSD. Heterogeneity of surfaces as reflected in the multifractal analysis will also be discussed.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 337-350, 1997
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    Davydov solitons in proteins Contribution to the Proceedings of the 2nd Congress of the International Society for Theoretical Chemical Physics at New Orleans Louisiana April 9-13 1996. (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 351-377 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The mechanism for energy and signal transport in proteins as suggested by Davydov is discussed. The idea is based on a coupling of amide-I oscillators to acoustic phonons in a hydrogen-bonded chain. Results as obtained with the usually used ansätze are discussed. The quality of these states for an approximate solution of the time-dependent Schrödinger equation is investigated. It is found that the semiclassical ansatz is a poor approximation, while the more sophisticated |D1〉 state seems to represent the exact dynamics quite well. Calculations at a temperature of 300 K for one chain, as well as for three coupled ones (as they are present in an α-helix), are presented and discussed. From the calculations, it is evident that Davydov solitons are stable for reasonable parameter values at 300 K only for special initial excitations close to the terminal sites of the chain. However, for soliton formation, it is not necessary that the initial excitation occurs at the chain end which has its C(DOUBLE BOND)O group directly coupled to the lattice as it is the case for T=0 K. At higher temperatures, solitary waves can be formed from both chain ends. Since the model for temperature effects used was criticized from the theoretical point of view, we suggest an improved theory for temperature effects. Finally, we discuss recent experimental findings which indicate that normal modes describing the N(SINGLE BOND)H stretch and its coupling to the hydrogen bonds should be considered in addition to the amide-I vibration.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 351-377, 1997
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    Outlines of a general framework of cancer initiation in the cell (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 379-385 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: According to the central dogma of molecular biology, information flows in the living cell from DNA through RNA to proteins. Therefore most investigations of cancer initiation try to explain these effects by carcinogen binding to, or radiation hits on, DNA which lead to the first steps of the malignant transformations. On the other hand, recent detailed theoretical investigations have shown that proteins are good disordered hopping conductors (their conductivity is in the order of good conducting amorphous glasses). Their conductivity can be substantially influenced by binding of chemicals or by the effects of radiation if they cause conformational changes (as recent calculations have shown). These effects can also destroy bonds or generate new bonds in proteins. If the affected proteins are regulatory proteins, they can be inactivated in both ways. Namely, on the basis of Warburg's experiments, one can postulate that if the hindrance of oxygen metabolism leads to fermentation, and with it to the malignant transformation, this means also the hindrance of electron flow in the Szent-Györgyi-Krebs cycle. In other words the hindrance of electron transport in this cycle most probably has the same effect as the lack of oxygen, which in this way most probably leads again to a malignant transformation. Finally the inactivation of regulatory enzymes can influence also the regulation of the expression of oncogenes. If in this way oncogenes become overactivated (or antioncogenes become inactive), the changes started by the inactivation of regulatory enzymes become hereditary. It seems that if we look at the cell as a complicated self-regulatory system, primary changes both at their DNA or regulatory protein molecules caused by external agents can disturb its self-regulation and transform it in this way into another stationary, possibly precancerous, state.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 379-385, 1997
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    Computer simulation of DNA sequential correlations (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 387-392 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: To obtain new insight into the nature of the correlations in distributions of nucleotides in DNA sequences, an efficient algorithm is presented by means of which one can generate nucleotide sequences with prescribed correlational properties. It is demonstrated in the case of human T-cell receptor beta chain gene segment that by extracting a finite number of parameters from the natural sequence one can generate artificial sequences which reproduce the correct correlational properties. It is shown how the apparent long-range correlations, or - what is equivalent - the 1/f form of the spectral density result due to the arrangement of DNA segments with different functional roles which also differ in composition in terms of nucleotide classes. This approach enables one to get under control the impact of statistical fluctuations which represent a major obstacle in the analyses of finite natural sequences.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 387-392, 1997
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    Two approaches to stochastic rate theory (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 393-401 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A comparison is made between two approaches to a Kramers-type reaction rate theory. The usual one is based on a linear coupling model between a particle and the medium oscillators. Use is made of two different separable reaction coordinates in the absence and presence of coupling, respectively. A more general model consists of assuming an arbitrary (nonlinear) coupling between the reactant and medium, making use of a single (curvilinear) reaction coordinate of the entire many-dimensional system (reactant+medium). A comparison with the exact dynamic rate theory is made, showing its equivalence with the generalized stochastic theory.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 393-401, 1997
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    Comprehensive strategy for the calculation of overlap integrals with Slater-type orbitals (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 881-889 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A strategy is presented for the calculation of two-center overlap integrals over Slater-type orbitals. Displaced orbitals are expanded in spherical harmonics with Löwdin α-functions as coefficients. The exponentials in the α-functions are expanded, leading to representation in terms of stored E and F matrices. For a given precision, the number of terms needed for each orbital for a specified harmonic, and its displacement multiplied by its screening constant, is predetermined and stored. A survey of these data is presented. The one-dimensional integration needed for the overlap is done by Gauss-Legendre numerical integration over the interior region and analytically over the exterior. Complete stability is achieved and excellent results obtained. Implications for all multicenter molecular integrals are apparent. © 1997 John Wiley & Sons, Inc.
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    Calculation of NMR shielding tensors based on density functional theory and a scalar relativistic Pauli-type Hamiltonian. The application to transition metal complexes (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 899-918 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This article deals with the calculation of the shielding tensor of nuclear magnetic resonance (NMR) spectroscopy based on a scalar relativistic two-component Pauli-type Hamiltonian. A complete formulation of the method within the framework of the gauge including atomic orbitals (GIAO) is given. Further, an implementation, based on density functional theory (DFT) is presented. The new method is applied to the 17O shielding in transition-metal oxo complexes [MO4]n- (M = Cr, Mo, W; Mn, Tc, Rh; Ru, Os) and to the metal chemical shift in transition-metal carbonyls M(CO)6 (M = Cr, Mo, W). This represents the first calculation of heavy-element shifts that is based on a relativistic first-principle quantum mechanical method. The inclusion of relativity is crucial for a proper description of ligand and metal shieldings in 5d complexes, but it is also important in 4d complexes. Limitations of the method, among them the neglect of the spin-orbit coupling, are discussed in detail. © 1997 John Wiley & Sons, Inc.
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    Substitution effects by SCF and Hückel theory (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 919-927 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A basic ansatz for the dipole moment has been programmed in Hückel theory and used to calculate some field-dependent properties. This is related to fundamental properties of shaped potentials rather than a good representation of real molecular properties. Limiting values may be meaningful and have been compared with semiempirical and SCF calculations. Coulson and Longuett-Higgins-style Coulomb integral perturbations were calculated. These give clear molecular design indications which are partially backed up by small-scale SCF calculations, using perturbations of the nuclear charge. This work is not intended to be comparable to good ab initio calculations but to point to rough and ready geometrical models of electrical susceptibility. © 1997 John Wiley & Sons, Inc.
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    Electrostatic medium effects and formal quantum structure-activity relationships in apomorphines interacting with D1 and D2 dopamine receptors (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 997-1002 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The binding of apomorphines (AM) to D1 and D2 dopamine receptors is analyzed through a formal quantum structure-activity relationship method. The calculations were carried out at the CNDO/2 level of the molecular orbital theory with a continuum representation of environmental effects. The results show that the D1 receptor affinity variation is related to the variation of the electron-donating capacity of a C atom of the hydroxylic region of apomorphines in a low-polarity medium. The N-chain probably interacts with a hydrophobic region of the receptor. It is also concluded that the poor results for the D2 binding affinity are explained by errors in the experimental measurements. Finally, it is proposed that future structure-activity relationship studies must be carried out for media of different polarities. © 1997 John Wiley & Sons, Inc.
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    On alternant molecules with identical energy spectra: Isospectral molecules (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 62 (1997), S. 167-169 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: It is shown that if a pair of alternant molecules are isospectral (they have identical energy spectra) in the topological - Hückel - approximation they are also isospectral, taking into account the electron correlation. The proof is given in the AMO approximation using a Hubbard Hamiltonian. © 1997 John Wiley & Sons, Inc.
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    Electron reorganization in chemical reactions: Pair population analysis along concerted reaction path of allowed and forbidden pericyclic reactions (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 62 (1997), S. 171-176 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The recently proposed pair population analysis was applied to the study of electron reorganization in the course of chemical reactions. The studied reactions involved a series of pericyclic reactions, both forbidden and allowed, and attention was devoted mainly to the evaluation of the specific differences between the allowed reactions and the forbidden ones. It was demonstrated that while the mechanism of allowed reactions can be visualized as a simple cyclic shift of the bonds the electron reorganization in forbidden reactions is much more complex and involves the considerable changes in the character of the wave function during the process. © 1997 John Wiley & Sons, Inc.
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    Oscillators in one and two dimensions and ladder operators for the Morse and Coulomb problems (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 62 (1997), S. 177-183 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We exhibit that the radial eigenfunctions of a 2D-harmonic oscillator (2DHO) may be regarded as 1D-harmonic oscillator (1DHO) matrix elements. From this simple fact and using as a starting point the ladder operators â± for 1DHO, we obtain ladder operators for 2DHO. Furthermore, by using the relationship between the Coulomb and Morse problems with a 2DHO, we are able to obtain the ladder operators for the former problems without explicitly recurring to the factorization method. Some uses of the technique presented are suggested. © 1997 John Wiley & Sons, Inc.
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    Discrete variable representation method applied to the determination of rotation-vibration bound states of NO2 (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 62 (1997), S. 199-211 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The discrete variable representation method is applied to the determination of the rotation-vibration energy levels of the fundamental electronic state of NO2. The Hamiltonian is expressed in Johnson hyperspherical coordinates and developed on a DVR basis for each internal coordinate, while parity-adapted linear combinations of Wigner functions are used to describe the rotational motion. The diagonalization of the Hamiltonian matrix is performed using the Lanczos algorithm for large symmetric and Hermitian matrices. Results for rovibrational states up to J = 11 for the first five vibrational energy levels are presented. © 1997 John Wiley & Sons, Inc.
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    Internal rotation study of some sixfold barrier molecules (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 62 (1997), S. 213-221 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Molecular orbital calculations of sixfold barriers in nitromethane, methyl boron difluoride, and trifluoronitromethane were performed by various Hartree-Fock and electron correlation methods. In those calculations, staggered and eclipsed conformations are of primary concern. These results indicated that for CH3NO2 and CH3BF2 the staggered conformations are more stable, while CF3NO2 has a more stable conformation in an eclipsed form. Both conformations do not differ significantly, which may account for the low internal rotational barrier of each molecule. Values of the barrier calculated by the Møller-Plesset perturbation and the quadratic configuration interaction methods did not match the experimental results. However, better internal rotational barrier values of each molecule were observed when the improved better basis sets and the Hartree-Fock method were selected. © 1997 John Wiley & Sons, Inc.
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    13-atom Ni-Al alloy clusters: Structures and dynamics (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 62 (1997), S. 185-197 
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    ISSN: 0020-7608
    Keywords: alloy clusters ; isomers ; homotops ; isomerization ; meltinglike transition ; surface melting ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Structural and dynamical properties of model 13-atom NinAlm alloy clusters derived from a many-body potential are presented and discussed. Characterization of the structures corresponding to a given stoichiometric composition (i.e., chosen number of Ni and Al atoms) is carried out in terms of isomeric (geometric) forms and different distributions of the two types of atoms between the sites of a chosen isomer. We use the term homotops (“the same topography or geometry”) to label the structural forms that differ only by these distributions. The number and the energy spectra of the homotops are sensitive functions of the stoichiometric composition and isomeric form. Similarly to homogeneous clusters, alloy clusters undergo a solid-to-liquidlike transition as their energy is increased. Individual stages in the transition, such as isomerizations involving only surface atoms, isomerizations involving all atoms, surface melting (in a system as small as 13 atoms), and complete melting are identified and characterized. The actual occurrence of some or all of these stages in the meltinglike transition of a given cluster depends on the character of the energy spectra of its homotops, i.e., ultimately, on its stoichiometric composition. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 62: 185-197, 1997
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    Implementation of gradient formulas for correlated gaussians: He, ∞He, Ps2, 9Be, and ∞Be test results (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 62 (1997), S. 223-235 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New formulas in the basis of explicitly correlated Gaussian basis functions, derived in a previous article using powerful matrix calculus, are implemented and applied to find variational upper bounds for nonrelativistic ground states of 4He, ∞He, Ps2, 9Be, and ∞Be. Analytic gradients of the energy are included to speed optimization of the exponential variational parameters. Five different nonlinear optimization subroutines (algorithms) are compared: TN, truncated Newton; DUMING, quasi-Newton; DUMIDH, modified Newton; DUMCGG, conjugate gradient; and POWELL, direction set (nongradient). The new analytic gradient formulas are found to significantly accelerate optimizations that require gradients. We found that the truncated Newton algorithm out-performs the other optimizers for the selected test cases. Computer timings and energy bounds are reported. © 1997 John Wiley & Sons, Inc.
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    Molecular and biomolecular electronics (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 62 (1997), S. 237-238 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: No abstract.
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    Introduction (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 1-5 
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    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes:    © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 1-5, 1997
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    Force balance equations in inhomogeneous classical and quantal liquids (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 21-29 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Inhomogeneous liquids in the presence of an external potential are considered. Exact force balance equations are written explicitly for (a) the classical case with pairwise interactions and (b) the ground-state quantal case of fermions with a general interaction, which embraces the Coulomb repulsion for electrons. Illustrative examples are given in both cases (a) and (b). Finally, a link between (a) and (b) is forged by considering the case of ensembles of finite systems.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 21-29, 1997
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    Evolution of atomic-molecular eigenchannels (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 31-33 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chemical reactions - as well as other collision processes - proceed generally from input elements condensing into a transitional complex and then dissociating into new fragments. Viewing the complex formation as reciprocal to its fragmentation combines them into conjugate elements of a single process, namely the complex evolution from a compact to a fragmented form, as its radius of inertia expands. As the wave functions of an atomic electron resolve conveniently into their radial and spherical-harmonic elements, so do those of multiparticle complex resolve into radial and hyperspherical-harmonic parts. Their numerical integration becomes thus accessible without resort to independent-particle or perturbative approximations. This approach displays a complex progressive branching into fragmentation channels. Evidence from small prototypes has shown each branching step to involve only a modest subset of the infinite harmonics set.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 31-33, 1997
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    Back-of-envelope derivation of the analytical formulas of the atomic wave functions of a D-dimensional atom (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 35-42 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A simple algebraic manipulation is presented for obtaining the analytical rectangular coordinate expressions of the atomic orbital wave functions with angular quantum number l of a D-dimensional atom, where no hyperspherical harmonics or any differential calculus is involved. A general expression of the D-dimensional f-orbitals is given which supplements the previously obtained result of D-dimensional d-orbitals.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 35-42, 1997
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    Third-order many-body perturbation theory for intermolecular interactions. I. Hartree-Fock level (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 43-51 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A zero-order wave function of a dimer is defined as the antisymmetrized product of monomer Hartree-Fock wave functions. A symmetry-adapted many-body perturbation theory is developed up to the third order to obtain interaction energies at the Hartree-Fock level. Correlation effects are accounted for at the second order. The theory is based on second quantization to ensure full symmetry forcing. Intermolecular overlap effects are handled by the biorthogonal formulation. Test calculations on dimers of He, H2, HF, and water show that the third-order results are very accurate. No “instability” due to the use of biorthogonal orbitals was observed.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 43-51, 1997
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    Nonadiabatic effects in multiphoton dissociation dynamics (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 53-61 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Nonadiabatic effects resulting from very short rise times (few femtoseconds) of intense (tens of TW/cm2) laser pulses may enhance in an unexpected way dissociation rates of molecules interacting with such radiation fields. Starting from a given initial vibrational level, the wavepacket describing the molecule-plus-field system is spread over several resonances (instead of a single one predicted when the laser is adiabatically switched on) interfering during the excitation process. The article reviews typical signatures of the time-dependent nonadiabatic behaviors of vibrational states' survival probabilities and of fragments' kinetic energy spectra. A H2+ molecular ion irradiated by short intense laser pulses in the UV absorption wavelength regime is taken as an illustrative example. A possibility of dissociating the system using a single photon of 532 nm wavelength is devised, with the peculiarity that the energy carried by this photon is not enough for the fragmentation to occur. The suggested mechanism, which may be called below threshold dissociation, refers to a highly nonadiabatic switching on of the laser, leading to the temporal excitation of some resonances with efficient decay rates.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 53-61, 1997
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    An implementation of RI-SCF on parallel computers (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 63-69 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The resolution of the identity (RI) approximation to the Hartree-Fock method was implemented within the NWChem suite of ab initio programs for parallel computers. After a description of the method, a detailed account of the implementation is given. We present a sample calculation and compare its performance and accuracy to an “exact” direct SCF calculation. Problems and limitations of the method are also discussed.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 63-69, 1997
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    Time evolution of CO vibrational populations during photodesorption by light pulses (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 71-83 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We describe the direct photodesorption of CO from the Ni(001) metal surface during the absorption of a short pulse of UV light by the adsorbate and account for the dynamics of the desorbing species coupled to electronic excitations of the substrate, which lead to energy dissipation. The interaction potentials and couplings for the ground and excited states are obtained from electronic structure calculations and from experimental information. The time evolution of CO vibrational populations is studied for propagating wavepackets for the adsorbate-substrate complex with a split-operator algorithm, followed by a perturbative treatment of dissipation and response to the light pulse. Direct photodesorption is found to occur predominantly in the excited electronic state and is compatible with dissipation. Results are presented for CO photodesorption by Gaussian pulses with several durations to show the effect of light pulse shapes on the time evolution of populations. Shorter pulses in the femtosecond range are shown to give relatively larger populations of excited vibrational states during the desorption of CO.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 71-83, 1997
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    Reaction field spectral shifts with semiempirical molecular orbital theory (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 143-155 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A macroscopic solution polarization free-energy functional is combined with semiempirical molecular orbital theory to study shifts of electronic absorption energies for several molecules in solution. The present method requires calculation of the induced electrostatic potential on the van der Waals surface and this calculation is implemented in a new way. The combined method is tested by calculating absorption energy shifts for several molecules of standard interest. We find the physically reasonable result that there is a correlation between the absorption energy shift and the magnitude of the dipole moments of the initial and final states involved in the absorption transition.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 143-155, 1997
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    On intra- and interpair electron correlation in LiF2 (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 171-174 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This article presents the intrapair and interpair electron correlation energies of LiF2. The total interpair correlation energy predominates. Hence, in building models for correcting post-Hartree-Fock calculations to obtain accurate electron correlation energies, the interpair electron correlation energy must be considered. Based on this result and our previous results, a fundamental assumption underlying the so-called higher-level correction in the Pople G1 the G2 theory is flawed.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 171-174, 1997
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    Boundary integral methods for the Poisson equation of continuum dielectric solvation models (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 121-141 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This article tests a dielectric model for the variation of hydration free energy with the geometry of complex solutes in water. It reexpresses the Poisson equation of the model to examine the basic aspects of boundary integral methods for these problems. It compares eight examples of dielectric model potentials of mean force in water with numerical results obtained from molecular scale models by simulation. Instructive and physical results are obtained but the model overstabilizes attractive, ion-pairing configurations. The article describes the algorithms, alternative to those in the literature, used here for high-precision solutions of that Poisson equation. Anticipating multigrid boundary integral approaches for similarly accurate treatment of larger solution complexes, the adaptation of spatial resolution is discussed. Finally, the statistical mechanical theory of the model is discussed together with a new proposal for describing the molecular detail of the solvation properties: integrating-out a probe solvent molecule using the dielectric model. The appendices give formal results relevant to periodic boundary conditions and infinite area surfaces such as solution interfaces and membranes.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 121-141, 1997
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    Some aspects on the development of the natural sciences and their importance for modern society and for our global environmentThe first four sections of this article are based on a series of lectures given in Taiwan, May 7-14 1995 on the invitation of the National Science Council of the Republic of China and they and they will be translated into Chinese and printed in the periodical Chemistry published in Taiwan. The full article was presented as a plenary lecture at the Second International Congress in Theoretical Chemical Physics in New Orleans, April 8-13, 1996. (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 157-169 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A brief review is given of the development of modern sciences from the early 1800s to the establishment of modern quantum theory around 1925 leading to modern theoretical chemical physics. Special attention is given to the interplay between mathematics, physics, and chemistry and to show how the development in one science strongly influences the development in the other sciences. A special section is devoted to the interplay between basic and applied research and to the interesting phenomenon that one may very likely get more and better technological applications if basic research is left to flourish on its own. In this connection, the relation between teaching and basic research is also discussed. Finally, the importance of modern science for the protection of our global environment is briefly reviewed.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 157-169, 1997
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    Ab initio propagator analysis of the valence double-ionization spectra of propyne (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 175-182 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Double-ionization energies, for transitions from the ground state of the neutral propyne molecule to both singlet and triplet states of its dication, are investigated theoretically with the ab initio second-order algebraic diagrammatic construction [ADC(2)] propagator method. The results are compared with a previous study which reported both experimental data obtained from double-charge-transfer (DCT) spectroscopy and their analysis with semiempirical theory. The ADC(2) predictions match almost all the experimental peaks well. In the lower-energy range, for transitions to dication states up to 7 eV above the ground state, ADC(2) predictions indicate that significant energy separations of those dication terms dominated by a common electronic configuration are responsible for previous difficulties in the assignment of peaks in that region. At higher energies, both configuration interaction and satellite ionizations are significant.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 175-182, 1997
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    Studies on the electronic structure and chemical bond of urea-nitrate (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 247-248 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: It is well known that urea-nitrate (UN) is a white solid complex prepared by urea with nitric acid, which is thus usually written as U⋅HNO3, (U--urea). Now it has widely been applied to fertilizer manufacture, chemical washing, petroleum opening, and other fields in industry because of its solubility in water into the original materials, i.e., urea and nitric acid. Up to now little is known about the electronic structure and chemical bond of UN. Therefore in this study the electronic structure of UN has been calculated by the SCC-DV-Xα method and its infrared and ultraviolet absorption bands and XPS binding energy have been investigated. On the basis of these, the chemical bond of UN has been discussed and a chemical formula for UN, [UH]+NO3-, to be named uronium nitrate, is proposed.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 247-248, 1997
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    Tunneling dynamics of one- and two-dimensional cubic oscillators with randomly fluctuating harmonic force constants: A numerical experiment This paper is dedicated to Professor Mihir Chowdhury on the occasion of his 60th birthday. (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 403-409 
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    ISSN: 0020-7608
    Keywords: tunneling dynamics ; tunneling through fluctuating barrier ; tunneling rate ; time-dependent cubic oscillator ; random cubic oscillator ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The tunneling dynamics of one- and two-dimensional cubic oscillators having randomly fluctuating harmonic force constants (Kt) are studied numerically by invoking the time-dependent Fourier grid Hamiltonian method. The influence of the frequency and strength of the fluctuation on the tunneling probability and tunneling rate is analyzed. The predicted nature of the influence depends upon whether the cubic oscillator is one- or two-dimensional. The possibility of mapping the proton-transfer systems onto the present model is explored.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 403-409, 1997
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    Box orbitals for extended systems (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 411-420 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A linear scaling of the number of nonzero integrals in extended systems calculations and the solution of the difficult cutoff threshold problems in the integral evaluation of periodic HF computations could be solved by the usage of orbitals with a finite extension. The present work proposes the usage of Box orbitals, defined inside spheres centered on the nuclei. Preliminary tests on small systems (atoms and H2+) were performed. The results are very encouraging, since, in most cases, the Box orbitals give better results (giving results of equivalent quality in the worse cases) than do the classical Gaussian orbitals. No spurious effects were encountered.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 411-420, 1997
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    Extension of the LAP functional to include parallel spin correlation (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 427-446 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetic energy density-dependent correlation functional LAP1 is extended to include parallel-spin correlation beyond the exchange level. Two exchange-correlation schemes are considered, combining the new correlation functional (LAP3) with the GGA exchange of Becke and the GGA exchange of Perdew. Extensive tests on molecules and hydrogen-bonded systems are presented and discussed elucidating the role of parallel-spin correlation in different cases. Its inclusion in the LAP functional leads, on average, to a slight improvement of the calculated binding energies and equilibrium geometries of molecules. Particularly high sensitivity of the energy results on the relative share of parallel-spin correlation is observed for aromatic molecules and for systems involving weak hydrogen bonds.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 427-446, 1997
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    On the electronic structure of Cu(H2O)62+ (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 453-458 
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    ISSN: 0020-7608
    Keywords: hexisa aqua copper cation ; charge transfer excited states ; 3d→3d excited states ; basis sets ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electronic structure of the ground state and the doublet excited states due to 3d→3d transitions and charge-transfer transitions from ligand to copper of Cu(H2O)62+ are investigated by ab initio calculations. The excited states corresponding to the 3d→3d transitions are calculated to be 1.1-1.4eV above the ground state and this is in good agreement with experiment. The charge-transfer excited states are not so easily determined as are the 3d→3d states, and they are described as an electron transfer from an orbital localized on each water. We have focused our attention on the description of these excited states. The charge-transfer excitations are predicted to start around 6.5 eV for Cu(H2O)62+.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 453-458, 1997
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    HNNH3, a new possible isomer of N2H4: An ab initio study (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 447-452 
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    ISSN: 0020-7608
    Keywords: N2H4 ; isomer ; ab initio calculation ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ab initio studies applying the 3-21G, 6-31G, and 6-31G** basis sets and also including the MP2 correction were carried out on H2NNH2, HNNH3, and the transition state of the reaction H2NNH2(DOUBLE BOND)HNNH3. First, the geometries of molecules were optimized using the theoretical methods mentioned in the restricted Hartree-Fock (RHF) scheme. The energies of the molecules corresponding to RHF/6-31G** geometries were subsequently calculated including electron-correlation effects at the level of the second-order Møller-Plesset (MP2) perturbation theory. The vibrational frequencies, net charges, and dipole moments were obtained from the theoretical calculations. The results of our calculations indicate unambiguously that H2NNH2 is thermodynamically more stable than is HNNH3. On the other hand, an isolated HNNH3 molecule once created would be stable since barriers for its unimolecular isomerization and decomposition are relatively high. But HNNH3 is unlikely to be isolated in measurable amounts because of bimolecular tautomerization. Nevertheless, HNNH3 can be considered as an intermediate in chemical processes involving N2H4.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 447-452, 1997
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    Polyiodide chains in crystalline organic iodides: Ab initio Hartree-Fock crystal orbital study (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 473-479 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hartree-Fock crystal orbital calculations of two crystalline organic iodides, tetrathiafulvalenium triiodide (TTF∗I3) and dipyridinium decaiodide (NHC5H5)2∗I10, were carried out. The former crystal contains no true polyiodide chains, whereas such chains are present in the latter crystal. In such a way, the effect of the polyiodide chain formation on the electronic structure of crystalline organic iodides was studied. The present calculations show that crystalline organic iodides with polyiodide chains could, in principle, be quasi-one-dimensional semiconductors. A polyiodide chain could be a carrier of semiconductivity only when it is formed by fully charged iodide anions (no charge transfer from the chain).   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 473-479, 1997
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    Studies on the band structures of some low-temperature superconductors (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 459-472 
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    ISSN: 0020-7608
    Keywords: low-temperature superconductors ; tight-binding energy-band calculations ; superconducting transition temperatures ; chemical bondings ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the present article, the electronic energy-band structures of 20 series of low-temperature superconductors were investigated employing the tight-binding method within the extended Hückel approximation. The energy bands, the densities of states, and the crystal orbital overlap populations of them are discussed. It is found that, for the crystals in the same series with the same structure type and the component elements in the same group of the periodic table, their overall energy-band structures are similar to each other. The analysis of their chemical bondings shows that the stronger bonding is generally correlated with the lower superconducting transition temperature to some extent. The higher Tc's of 4d metals or compounds relative to those of the corresponding 5d crystals are mainly due to the difference of the electronegativities of metal atoms, while the steric effects play a more important role in the higher Tc of 4d crystals than do those of the corresponding 3d crystals.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 459-472, 1997
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    Introduction to the workshop on properties of molecules in strong magnetic fields (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 495-496 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: No abstract.
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    List of participants (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 497-499 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: No abstract.
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    Effect of different subsets on convergence patterns of hyperspherical harmonic expansion for the S states of the helium atom (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 661-668 
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    ISSN: 0020-7608
    Keywords: Hyperspherical harmonics ; radial correlation ; angular correlation ; l limits ; 1S and 3S states of the helium atom ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Effects of different subsets on convergence patterns of hyperspherical harmonic (HH) expansions for the low-lying 1S and 3S states of the helium atom have been investigated with the correlation-function-hyperspherical-harmonic-generalized-Laguerre-function (CFHHGLF) method by successively introducing HH subsets with the fixed three-dimensional angular momentums (l) into the atomic wave functions. The eigenenergies given by the HH subsets of l=0, 1, 2, and 3 are in good agreement with the best s-, sp-, spd-, and spdf limits of variational configuration interaction (CI) calculations, respectively. The final eigenenergies of the ground state as well as the examined low-lying excited 1S and 3S states are quite close to the exact Hylleraas CI (HCI) values at the sixth decimal place. Moreover, l=0 and l≠0 expansion results also tell us that it is not necessary to take into account too many HHs at the given l, especially for higher l, and that the more the absolute electron correlation energies the bigger l it takes to obtain precise eigenenergies.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 661-668, 1997
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    Role of oxygen content in electronic structures of Ba0.6K0.4BiO3-δ (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 703-710 
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    ISSN: 0020-7608
    Keywords: Superconductor ; Ba0.6K0.4BiO3-δ ; oxygen content ; band structure ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The band structure calculations on the K-doped superconductor Ba0.6K0.4BiO3-δ were carried out, and the effect of the oxygen content on its electronic structures was studied in the present work. The results show that the variation in the oxygen content caused by the partial substitution of K for Ba has a great effect on its electronic structure. The oxygen vacancies cause the saddle point singularity to be displaced gradually as the oxygen content is decreased, whereas the band structure is only translated a little and remains unchanged in shape, which reflects the non-rigid-bandlike behavior of Ba0.6K0.4BiO3-δ in the presence of the oxygen vacancies. When the saddle point singularity is displaced and lies at the Fermi level Ef, the total density of states at Ef, N(Ef), has the highest value which is twice as large as that of the Ba0.6K0.4BiO3 compound without the oxygen vacancies. These results reveal the important role of the oxygen content in the Ba-K-Bi-O superconducting system.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 703-710, 1997
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    The quantum theory of radiation (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 735-735 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: No abstract.
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    Symmetric group approach to relativistic CI. IV. Representations of one-electron spin operators and their products in a symmetric group-adapted basis of N-electron spin functions (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 737-737 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: No abstract.
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  • 93
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    Theoretical studies of inclusion complexes of β-cyclodextrin with methylated benzoic acids (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 711-719 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: AM1 semiempirical molecular orbital calculations have been performed on the inclusion complexes of β-cyclodextrin (β-CD) with methylated benzoic acids in two orientations, the “head-first” and “tail-first” positions. In the former, the CO2H group points toward the primary hydroxyls of the CD. In the latter, it points away from them. Out of 30 possible inclusion complexes, AM1 results predict only three clearly stable inclusion complexes. These are β-CD with 4-methyl benzoic acid in the head-first position, β-CD with 2,4-dimethyl benzoic acid in the head-first position, and β-CD with 3,5-dimethyl benzoic acid in the tail-first position. The orientations of the stable inclusion complexes correlate with the total number of intramolecular hydrogen bonds and intermolecular hydrogen bonds. The stability of a complex also correlates with the closeness of the host and guest geometries in the complex to their isolated molecule geometries.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 711-719, 1997
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    Vibronic instability of molecular configurations in the Hartree-Fock-Roothaan approximation (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 65 (1997), S. 37-48 
    Details
    ISSN: 0020-7608
    Keywords: pseudo-Jahn-Teller effect ; vibronic coupling ; molecular geometry ; energy surfaces ; random-phase approximation ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The traditional description of pseudo-Jahn-Teller molecular configuration instability based on Bader's formula for the curvature of the adiabatic potential is reconsidered in order to make it consistent with straightforward calculations of the ground-state energy surface within Hartree-Fock-Roothaan approximation. The proposed approach employs floating molecular orbitals constructed by “frozen LCAO” coefficients (computed in the reference geometry) and floating atomic orbitals, which allows one to exclude the vibronic mixing with the excited states irrelevant from chemical point of view. The relaxation (vibronic) contribution to the instability, expressed in terms of one-electron quantities, involves two sets of orbital vibronic constants. These are, respectively, defined as matrix element derivatives of correct and “frozen LCAO” Fock operators between occupied and unoccupied molecular orbitals. The canonical form of the relaxation contribution can be achieved when the vibronic interaction is presented as a mixing between the ground electronic state and the excited states calculated within the random-phase approximation   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 65: 37-48, 1997
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    The freeon theory of magnetism. I. The Heisenberg interaction (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 65 (1997), S. 287-297 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The freeon theory of magnetism is a viable alternative to the well-known Heisenberg theory. In particular, the freeon-exchange theory provides a deeper insight into the nature of the magnetic interaction than does the spin-exchange theory. In addition, it avoids the superfluous MS quantum number in zero-field splitting, the overcounting of spin states, the spin frustration, and the spin paradigm. The freeon-exchange theory employs the algebra of the symmetric group and/or the unitary group in place of the spin algebra. The basis vectors of freeon theory are the Gel'fand states which are uniquely labeled by Gel'fand diagrams; the latter provide both the electron configuration and the spin quantum number. Both the spin and the freeon formulations support the Landé interval rule. In this article, we apply freeon theory to transition-metal dimers, trimers, and tetramers; these are examples of molecular magnets which have applications to microcircuitry. The freeon theory follows the permutation-group principle laid down by Herman Weyl over one-half a century ago.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 65: 287-297, 1997
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    Comparison of electron propagator methods for calculating electron detachment energies of anions (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 65 (1997), S. 463-469 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Electron propagator methods for calculating vertical electron detachment energies of closed-shell anions are compared with respect to accuracy and efficiency. Examination of self-energy terms and numerical tests on typical anions show that the partial third-order (P3) quasi-particle approximation is superior to the third-order and outer valence Green's function methods in both respects.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 65: 463-469, 1997
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    Maximum principles in DFT from reciprocal variational problem (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 65 (1997), S. 499-501 
    Details
    ISSN: 0020-7608
    Keywords: density-functional theory ; variational principle ; reciprocal problem ; maximum principle ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Formalism of density-functional theory (DFT) is based on the calculus of variation. In the Hohenberg and Kohn theorem, a variational equation minimizing electronic energy with respect to an electron density is constructed. The calculus of variation allows one to formulate a problem which is reciprocal to an original one. Also, we may consider the problem of finding the electron density determining a given energy E=E[ρ] for a maximum number N=N[ρ] of the electrons forming the system. In this work, the reciprocal variational problem is discussed. Mathematical considerations are followed by a presentation of an application of the reciprocal problem (maximum entropy principle). Other possibilities of the applications are sketched.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 65: 499-501, 1997
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    Real-space multigrid methods for large-scale electronic structure problems (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 65 (1997), S. 531-543 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We describe the development and applications of a new electronic structure method that uses a real-space grid as a basis. Multigrid techniques provide preconditioning and convergence acceleration at all length scales and therefore lead to particularly efficient algorithms. The salient points of our implementation include: (i) new compact discretization schemes in real space for systems with cubic, orthorhombic, and hexagonal symmetry and (ii) new multilevel algorithms for the iterative solution of Kohn-Sham and Poisson equations. The accuracy of the discretizations was tested by direct comparison with plane-wave calculations, when possible, and the results were in excellent agreement in all cases. These techniques are very suitable for use on massively parallel computers and in O(N) methods. Tests on the Cray-T3D have shown nearly linear scaling of the execution time up to the maximum number of processors (512). The above methodology was tested on a large number of systems, such as the C60 molecule, diamond, Si and GaN supercells, and quantum molecular dynamics simulations for Si. Large-scale applications include a simulation of surface melting of Si and investigations of electronic and structural properties of surfaces, interfaces, and biomolecules.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 65: 531-543, 1997
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    Correlated relativistic calculation of the giant resonance in the Gd3+ absorption spectrum (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 65 (1997), S. 575-584 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The aim of the present study is to extend the multiconfiguration Dirac-Fock approach to include spin polarization in order to study magnetically ordered systems. Routines handling time-dependent ionization phenomena adapted to multilevel and multichannel autoionization processes have been developed and used to describe the giant resonance in the Gd3+ absorption spectrum. In our calculation of the complete energy structure of 4d94f8 configuration it is discovered that the majority of the oscillator strength associated with the 4d-4f transitions is limited to a relatively narrow spectral width, creating a giant resonance. Our calculations take account of the most important correlation effects, and the agreement with the experimentally observed giant resonance in gadolinium is quite good.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 65: 575-584, 1997
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    Low-energy electron scattering from a model H2 potential using finite elements in two dimensions (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 65 (1997), S. 591-600 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Schrödinger equation for the scattering of an electron by a hydrogen molecule is solved by the finite element method, in spherical coordinates, using fifth-order Hermite interpolating polynomials. The computational method is quite similar to the work of Shertzer and Botero [Phys. Rev. A 49, 3673 (1994), and references therein]. However, to study large systems, an effective one-particle dynamical equation is defined, unlike the procedure of Shertzer and Botero. To illustrate the basic computational procedure, a model electron-H2 interaction potential (static+exchange+polarization) is constructed and the K-matrix is calculated. A novel feature of the present method is the procedure for extracting the partial-wave amplitudes at a value of r, the size of which is fixed by the range of nonlocal potentials in the problem, and then propagating the scattering amplitudes out to an effective infinity where the converged K-matrix is determined.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 65: 591-600, 1997
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