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  • Animals  (2,869)
  • Theoretical, Physical and Computational Chemistry  (1,576)
  • AERODYNAMICS
  • 1995-1999  (4,544)
  • 1925-1929  (1)
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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Machine vision and applications 8 (1995), S. 187-193 
    ISSN: 1432-1769
    Keywords: Tracking ; Segmentation ; Pigs ; Animals ; Computer vision
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract An algorithm was developed for the segmentation and tracking of piglets and tested on a 200-image sequence of 10 piglets moving on a straw background. The image-capture rate was 1 image/140 ms. The segmentation method was a combination of image differencing with respect to a median background and a Laplacian operator. The features tracked were blob edges in the segmented image. During tracking, the piglets were modelled as ellipses initialised on the blobs. Each piglet was tracked by searching for blob edges in an elliptical window about the piglet's position, which was predicted from its previous two positions.
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  • 2
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    Springer
    Journal of molecular evolution 42 (1996), S. 183-193 
    ISSN: 1432-1432
    Keywords: Small-subunit ribosomal RNA ; Phylogeny ; Animals ; Fungi ; Plants ; Alveolates ; Heterokonts ; Stramenopiles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The evolutionary relationships of four eukaryotic kingdoms—Animalia, Plantae, Fungi, and Protista—remain unclear. In particular, statistical support for the closeness of animals to fungi rather than to plants is lacking, and a preferred branching order of these and other eukaryotic lineages is still controversial even though molecular sequences from diverse eukaryotic taxa have been analyzed. We report a statistical analysis of 214 sequences of nuclear small-subunit ribosomal RNA (srRNA) gene undertaken to clarify these evolutionary relationships. We have considered the variability of substitution rates and the nonindependence of nucleotide substitution across sites in the srRNA gene in testing alternative hypotheses regarding the branching patterns of eukaryote phylogeny. We find that the rates of evolution among sites in the srRNA sequences vary substantially and are approximately gamma distributed with size and shape parameter equal to 0.76. Our results suggest that (1) the animals and true fungi are indeed closer to each other than to any other “crown” group in the eukaryote tree, (2) red algae are the closest relatives of animals, true fungi, and green plants, and (3) the heterokonts and alveolates probably evolved prior to the divergence of red algae and animal-fungus-green-plant lineages. Furthermore, our analyses indicate that the branching order of the eukaryotic lineages that diverged prior to the evolution of alveolates may be generally difficult to resolve with the srRNA sequence data.
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  • 3
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    Springer
    Journal of molecular evolution 41 (1995), S. 238-246 
    ISSN: 1432-1432
    Keywords: Cellular slime molds ; Animals ; Fungi ; Plantae ; Maximum-likelihood method ; Evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The phylogenetic position of Dictyostelium inferred from 18S rRNA data contradicts that from protein data. Protein trees always show the close affinity of Dictyostelium with animals, fungi, and plants, whereas in 18S rRNA trees the branching of Dictyostelium is placed at a position before the massive radiation of protist groups including the divergence of the three kingdoms. To settle this controversial issue and to determine the correct position of Dictyostelium, we inferred the phylogenetic relationship among Dictyostelium and the three kingdoms Animalia, Fungi, and Plantae by a maximum-likelihood method using 19 different protein data sets. It was shown at the significance level of 1 SE that the branching of Dictyostelium antedates the divergence of Animalia and Fungi, and Plantae is an outgroup of the Animalia-Fungi-Dictyostelium clade.
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  • 4
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    Springer
    Journal of agricultural and environmental ethics 10 (1997), S. 249-267 
    ISSN: 1573-322X
    Keywords: Animals ; Asia ; consciousness ; Australia ; Hong Kong ; India ; Israel ; Japan ; New Zealand ; The Philippines ; Russia ; Singapore ; Thailand
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Philosophy
    Notes: Abstract The interactions between humans, animals and the environment have shaped human values and ethics, not only the genes that we are made of. The animal rights movement challenges human beings to reconsider interactions between humans and other animals, and maybe connected to the environmental movement that begs us to recognize the fact that there are symbiotic relationships between humans and all other organisms. The first part of this paper looks at types of bioethics, the implications of autonomy and the value of being alive. Then the level of consciousness of these relationships are explored in survey results from Asia and the Pacific, especially in the 1993 International Bioethics Survey conducted in Australia, Hong Kong, India, Israel, Japan, New Zealand, The Philippines, Russia, Singapore and Thailand. Very few mentioned animal consciousness in the survey, but there were more biocentric comments in Australia and Japan; and more comments with the idea of harmony including humans in Thailand. Comparisons between questions and surveys will also be made, in an attempt to describe what people imagine animal consciousness to be, and whether this relates to human ethics of the relationships.
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  • 5
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    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 1-10 
    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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  • 6
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    International Journal of Quantum Chemistry 61 (1997), S. 11-20 
    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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  • 7
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    International Journal of Quantum Chemistry 61 (1997), S. 21-34 
    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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  • 8
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    International Journal of Quantum Chemistry 61 (1997), S. 35-43 
    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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  • 9
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    International Journal of Quantum Chemistry 61 (1997), S. 45-54 
    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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  • 10
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    International Journal of Quantum Chemistry 61 (1997), S. 55-61 
    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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  • 11
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    International Journal of Quantum Chemistry 61 (1997), S. 63-65 
    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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  • 12
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    International Journal of Quantum Chemistry 61 (1997), S. 67-76 
    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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  • 13
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    International Journal of Quantum Chemistry 61 (1997), S. 77-83 
    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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  • 14
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    International Journal of Quantum Chemistry 61 (1997), S. 93-100 
    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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  • 15
    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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  • 16
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    International Journal of Quantum Chemistry 61 (1997), S. 101-105 
    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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  • 17
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    International Journal of Quantum Chemistry 61 (1997), S. 815-822 
    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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  • 18
    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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  • 19
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    International Journal of Quantum Chemistry 61 (1997), S. 823-833 
    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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  • 20
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    International Journal of Quantum Chemistry 61 (1997), S. 835-845 
    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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  • 21
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    International Journal of Quantum Chemistry 61 (1997), S. 859-863 
    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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  • 22
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    International Journal of Quantum Chemistry 61 (1997), S. 847-857 
    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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    International Journal of Quantum Chemistry 61 (1997), S. 865-879 
    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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  • 24
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    International Journal of Quantum Chemistry 61 (1997), S. 891-898 
    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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  • 25
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    International Journal of Quantum Chemistry 61 (1997), S. 929-933 
    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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    International Journal of Quantum Chemistry 61 (1997), S. 935-941 
    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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    International Journal of Quantum Chemistry 61 (1997), S. 943-952 
    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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    International Journal of Quantum Chemistry 61 (1997), S. 953-957 
    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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    International Journal of Quantum Chemistry 61 (1997), S. 959-980 
    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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    International Journal of Quantum Chemistry 61 (1997), S. 981-990 
    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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    International Journal of Quantum Chemistry 61 (1997), S. 991-996 
    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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    International Journal of Quantum Chemistry 62 (1997), S. 125-135 
    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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    International Journal of Quantum Chemistry 62 (1997), S. 137-151 
    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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    International Journal of Quantum Chemistry 62 (1997), S. 153-165 
    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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    International Journal of Quantum Chemistry 64 (1997), S. 85-93 
    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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    International Journal of Quantum Chemistry 64 (1997), S. 111-119 
    ISSN: 0020-7608
    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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    International Journal of Quantum Chemistry 64 (1997), S. 95-110 
    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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    International Journal of Quantum Chemistry 64 (1997), S. 183-191 
    ISSN: 0020-7608
    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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    International Journal of Quantum Chemistry 64 (1997), S. 193-203 
    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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    International Journal of Quantum Chemistry 64 (1997), S. 205-210 
    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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    International Journal of Quantum Chemistry 64 (1997), S. 223-230 
    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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    International Journal of Quantum Chemistry 64 (1997), S. 231-242 
    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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    International Journal of Quantum Chemistry 64 (1997), S. 211-222 
    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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    International Journal of Quantum Chemistry 64 (1997), S. 243-246 
    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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    International Journal of Quantum Chemistry 64 (1997), S. 263-269 
    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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    International Journal of Quantum Chemistry 64 (1997), S. 255-261 
    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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    International Journal of Quantum Chemistry 64 (1997), S. 249-254 
    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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    International Journal of Quantum Chemistry 64 (1997), S. 285-295 
    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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    International Journal of Quantum Chemistry 64 (1997), S. 297-300 
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    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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    International Journal of Quantum Chemistry 64 (1997), S. 271-283 
    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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    International Journal of Quantum Chemistry 64 (1997), S. 301-323 
    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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    International Journal of Quantum Chemistry 64 (1997), S. 325-336 
    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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    International Journal of Quantum Chemistry 64 (1997), S. 337-350 
    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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    International Journal of Quantum Chemistry 64 (1997), S. 351-377 
    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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    International Journal of Quantum Chemistry 64 (1997), S. 379-385 
    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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    International Journal of Quantum Chemistry 64 (1997), S. 387-392 
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    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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    International Journal of Quantum Chemistry 64 (1997), S. 393-401 
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    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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    International Journal of Quantum Chemistry 58 (1996), S. 637-643 
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    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A simple procedure is presented for obtaining the standard Young tableaux for the representation [(N/2) + S,(N/2) - S] of the permutation group ℒN for an N-electron system in spin state S directly from the spin branching diagram. We redefine the coordinate axes of the branching diagram to obtain a graph in terms of the partitions of the two-rowed Young diagram and define walks in this graph which yield directly the first rows of the allowed standard Young tableaux spanning a given representation when suitable weights have been assigned to the nodes in the graph. The allowed states are in a lexically ordered form and permit going easily from an index to an array and vice versa. © 1996 John Wiley & Sons, Inc.
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    International Journal of Quantum Chemistry 58 (1996), S. 645-655 
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    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The development of the idea of a chemical bond is traced from Frankland to Heitler and London and beyond with emphasis on how electrons came to be considered essential to explaining the bond. © 1996 John Wiley & Sons, Inc.
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    International Journal of Quantum Chemistry 58 (1996), S. 657-670 
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    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Starting with knowledge of the internal energy of a polyatomic system as a multidimensional function of the coordinates of the component atoms - the effective potential surface, one can explore the topography of this surface to find its stationary points and topology. Clusters are particularly effective vehicles for developing the methods of doing this, although it is essentially as easy to study small molecules as it is clusters, if the corresponding surfaces are already known. If the system is small enough, all the minima, the relevant saddles, and the corresponding reaction paths can be found; if the system is larger, then only statistical sampling methods can be applied. Such explorations can be used as efficient ways to test the physical plausibility of potential surfaces, e.g., to determine whether a surface developed to describe spectra is valid enough globally to be used for scattering studies. With the readily manageable potentials such as that composed of the sum of pairwise Morse interactions, it is now straightforward to explore how the form of the basic pair interactions affects the multidimensional topography of the surface. For systems of many particles, it is beginning to seem feasible to infer from topographical properties of the surface the extent to which a system undergoing cooling is either glass-forming or “focusing,” in the sense of going to a single structure or a small set of related structures. © 1996 John Wiley & Sons, Inc.
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    International Journal of Quantum Chemistry 61 (1997), S. 881-889 
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    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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    International Journal of Quantum Chemistry 61 (1997), S. 899-918 
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    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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    International Journal of Quantum Chemistry 61 (1997), S. 919-927 
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    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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    International Journal of Quantum Chemistry 61 (1997), S. 997-1002 
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    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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    International Journal of Quantum Chemistry 62 (1997), S. 167-169 
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    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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    International Journal of Quantum Chemistry 62 (1997), S. 171-176 
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    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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    International Journal of Quantum Chemistry 62 (1997), S. 177-183 
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    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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    International Journal of Quantum Chemistry 62 (1997), S. 199-211 
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    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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    International Journal of Quantum Chemistry 62 (1997), S. 213-221 
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    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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    International Journal of Quantum Chemistry 62 (1997), S. 185-197 
    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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    International Journal of Quantum Chemistry 62 (1997), S. 223-235 
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    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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    International Journal of Quantum Chemistry 62 (1997), S. 237-238 
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    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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    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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    International Journal of Quantum Chemistry 64 (1997), S. 21-29 
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    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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    International Journal of Quantum Chemistry 64 (1997), S. 31-33 
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    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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    International Journal of Quantum Chemistry 64 (1997), S. 35-42 
    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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  • 77
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    International Journal of Quantum Chemistry 64 (1997), S. 43-51 
    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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  • 78
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    International Journal of Quantum Chemistry 64 (1997), S. 53-61 
    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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    International Journal of Quantum Chemistry 64 (1997), S. 63-69 
    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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    International Journal of Quantum Chemistry 64 (1997), S. 71-83 
    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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    International Journal of Quantum Chemistry 64 (1997), S. 143-155 
    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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    International Journal of Quantum Chemistry 64 (1997), S. 171-174 
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    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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    International Journal of Quantum Chemistry 64 (1997), S. 121-141 
    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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  • 84
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    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
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    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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    International Journal of Quantum Chemistry 64 (1997), S. 175-182 
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    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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    International Journal of Quantum Chemistry 64 (1997), S. 247-248 
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    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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  • 87
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    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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    International Journal of Quantum Chemistry 64 (1997), S. 411-420 
    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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    International Journal of Quantum Chemistry 70 (1998), S. 189-197 
    ISSN: 0020-7608
    Keywords: atomic Hartree-Fock ; augmented Fourier basis ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We present a scheme for Hartree-Fock and related calculations on atoms using a Fourier basis augmented by an exponential function. All multiple sums in the variational energy expression are written as single sums over combinations of multiplications and convolutions. The computational cost of the method is thus practically linear in the number of basis functions. The results compare favorably with the most precise published results of numerical grid methods and variational calculations.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 189-197, 1998
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    International Journal of Quantum Chemistry 70 (1998), S. 205-217 
    ISSN: 0020-7608
    Keywords: potential energy surface ; transition structure ; nonrigid molecule ; symmetry group ; reaction path ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The symmetry group of a nonrigid molecule is related to that of the transition structure that is related to the rearrangement process which contributes to the “nonrigidity” of the molecular system. The resulting permutation/rotation/reflection groups for nonrigid molecules can be much larger in order than the usual Longuet-Higgins permutation/inversion group. A few examples are presented to illustrate the definition of the symmetry group for nonrigid molecules.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 205-217, 1998
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    International Journal of Quantum Chemistry 70 (1998), S. 219-239 
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We review some recent developments of high-order response theory and illustrate the utility of this theory for a selection of nonlinear properties.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 219-239, 1998
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  • 92
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    International Journal of Quantum Chemistry 70 (1998), S. 253-267 
    ISSN: 0020-7608
    Keywords: DFT ; carbonyloxyl radicals ; CASPT2 ; chemical reactions ; isomerizations ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The structure of the lowest electronic states of HCOO· in C2v and Cs symmetries were optimized employing density functional theory (DFT) methods with extended basis sets including up to f- (on C and O) and d- (on H) polarization functions. Generalized gradient functionals (BLYP) and adiabatically connected functionals (B3LYP and B3PW91) were employed for studying HCOO·, as well as the isomer HOCO· (trans), the dissociation limit H·+CO2, and the transition state for the decomposition. At the best DFT levels employed, the ground state of HCOO· is 2A1 (in C2v) with equal C—O bond lengths, while the low-lying 2B2 state is only about 4 kJ/mol above (without inclusion of zero-point energies). The broken-symmetry 2A′ state (with unequal C—O bond lengths, i.e., Cs symmetry) is predicted to be about 13 kJ/mol above the 2A1 state and to be a transition state for the isomerization HCOO· (2A1)→HOCO· (2A′), with the trans-HOCO· isomer about 55 kJ/mol more stable. These facts agree closely with the most recent CASPT2/ANO calculations on this system. Therefore, it is concluded that some DFT models can be used safely for the study of larger radicals of the same type (despite several drawbacks discussed at length in this study). B3PW91, using several basis sets, is subsequently applied to the study of the possible reaction mechanisms of acetyloxyl radical, which exhibits a much more complicated path than formyloxyl, due to the presence of the methyl group. The optimum structures of isomers with coplanar or perpendicular CH and CO bonds were obtained for CH3COO· and two saddle points identified on the path of decomposition into CH3· and CO2. On the other side, saddle points for isomerization into CH3OCO· and CH2COOH· were also located, and the decomposition of the former to CH3O·+CO investigated. Finally, the structure of the benzoyloxyl radical (C6H5COO·) and its possible decomposition products were investigated along the same lines.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 253-267, 1998
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    International Journal of Quantum Chemistry 70 (1998), S. 283-290 
    ISSN: 0020-7608
    Keywords: LiB ; spectroscopic constants ; excited states ; VBSCF ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The common correspondence between molecular orbital theory and resonance theory in the description of the electronic structure of a molecule is used to select valence bond (VB) structures constructing wave functions of the low-lying states of LiB and LiB+. The spectroscopic parameters of the low-lying states of LiB and LiB are determined by using the valence bond self-consistent field (VBSCF) method. For comparison, multconfiguration SCF (MCSCF) calculations for LiB are also carried out. If the overlap-enhanced orbitals are employed, a compact VB wave function can correctly describe bond making and bond breaking in the entire dissociation process for the low-lying electronic states of LiB. All calculations locate the ground state as 3Π. The VB calculation with 14 VB structures at the level of the basis set DH(s, p) predicts an excellent dissociation energy of 1.16 eV and vibrational frequency of 527 cm-1 for the ground state, which is in good agreement with previous high-level calculations with a large basis set. The effect of the basis set on the numerical quality of the VBSCF calculation is investigated. It is important for improving accuracy of the VB calculation to enlarge the basis set, although the VB treatment including more VB structures with a relatively small basis set needed in the nonorthogonal VB calculation can reasonably describe dissociation behavior for systems with few electrons. The chemical bonds in the ground state 3Π and the excited state (1)3Σ- have ionicities of 63.4 and 65.1%, respectively, while chemical bond in the first excited state 1Σ+ is mainly covalent. Other several low-lying states are also investigated by the VB and MCSCF methods.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 283-290, 1998
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    International Journal of Quantum Chemistry 70 (1998), S. 303-312 
    ISSN: 0020-7608
    Keywords: bithiophene ; internal rotation ; DFT calculations ; MP2 calculations ; Fourier-fitted torsional potentials ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The internal rotation of 2,2′-bithiophene was investigated within the density functional theory (DFT) approach. Fully optimized DFT torsional potentials are compared with Møller-Plesset (MP2) results which predict a fourfold potential with s-cis- and s-trans-gauche minima. DFT calculations fail in describing the energetics of the internal rotation because they favor planar vs. perpendicular conformers. Gradient-corrected functionals provide torsional potentials where the gauche minima have almost vanished and the s-cis↔s-trans interconversion barriers are twice as high as the barriers obtained at the MP2 level. The use of local functionals augments the shortcomings of the DFT approach. The gauche minima completely disappear and the rotational barriers are now about three times higher than the MP2 barriers. As an efficient computational approach, we suggest having geometries optimized at the DFT level and conformational energies evaluated via single-point MP2 calculations. The fitting of MP2//DFT energies to truncated Fourier expansions allows one to predict the torsional angles and the relative energies of the critical points of the rotational potential with an accuracy similar to that afforded by MP2 calculations including full geometry optimization.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 303-312, 1998
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    International Journal of Quantum Chemistry 70 (1998), S. 321-329 
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The geometries of the reactant, products, and transition state of the title reaction were optimized at the UHF and UMP2 levels with the double and triple zeta basis sets as well as polarization functions by using the energy-gradient method. The potential-energy barrier for this reaction is 3.73 kcal/mol at the UMP-SAC4 level of theory. The intrinsic reaction coordinate (IRC) was performed at the UMP2/6-311G** level. The changes of the geometry and the bound vibrational modes along the IRC were analyzed. To obtain a more reliable potential-energy curve for the study of the reaction dynamics, the UMP2 energy profile was refined along the IRC with the UQCISD(T) and UMP-SAC4 levels of theory. The theoretical rate constants calculated by the conventional and the variational transition-state theories at the UMP-SAC4 level agree approximately with the experimental values in the high-temperature range from 2000 to 3000 K and are not affected by the variation and quantum effects.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 321-329, 1997
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  • 96
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    International Journal of Quantum Chemistry 70 (1998), S. 341-350 
    ISSN: 0020-7608
    Keywords: alumina ; periodic SCF ; surface potential ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electronic structure of the (001) and (110) α-alumina surfaces was determined by periodic Hartree-Fock method in statically relaxed geometries. Both (001) and (110) surfaces generate specific surface states into the energy gap. Significant influence of charge-transfer effect on the surface-adsorbate potential is possible in both cases studied. The inclusion of the exponential part to the standard potential forms was suggested for the description of the interaction potential in such cases.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 341-350, 1998
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    International Journal of Quantum Chemistry 70 (1998), S. 359-365 
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A theoretical analysis of γ-Al2O3 (110) surface hydroxylation based on ab initio Hartree-Fock embedded cluster calculations was carried out. Both tetrahedral and octahedral Al sites were considered. These sites were modeled by a series of clusters of increasing size: Al8O3, Al12O5, and Al16O8, embedded in an array of point charges. The adsorption of water was found to be dissociative or nondissociative depending on the cluster size, although the mechanism clearly converges toward dissociation for the more reliable models in agreement with the experiment. This dependence can be explained in light of the basicity modification of surface oxide ions induced by the environment as well as by surface relaxation. Comparison of chemisorption energies suggests that the preferred site for hydroxylation is a low coordination tetrahedral aluminum.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 359-365, 1998
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  • 98
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    International Journal of Quantum Chemistry 70 (1998), S. 375-378 
    ISSN: 0020-7608
    Keywords: electronic structure ; catalytic properties ; Wangh-type anion ; heteropoly compounds ; DV-Xα method ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electronic structure of Waugh anion (NiMo9O32)6- has been calculated by the DV-Xα method. The electronic structure and catalytic behavior of the Waugh anion are discussed. At the same time, the difference in electronic structure and relationship in catalytic behavior between Waugh and Keggin anions are compared.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 375-378, 1998
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    International Journal of Quantum Chemistry 70 (1998), S. 395-405 
    ISSN: 0020-7608
    Keywords: intramolecular H bonds ; gas-phase stability ; continuum solvent ; solvation free energy ; point charge model ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformational properties of bilirubin present a considerable interest from the medical and biological points of view, because of the toxic pigment peculiar solubility features. Therefore, ab initio geometry optimizations at the 3-21G/SCF level were carried out on a few model-built structures of bilirubin, after substituting the methyl groups on the heteroaromatic rings with H atoms. The structures obtained show a varied network of H bonds, ranging from 0 to 6 H bonds for the lowest-energy conformer in vacuo. This conformer assumes a “ridge-tile” shape previously found in both MM/MD simulations [D. A. Lightner et al., J. Am. Chem. Soc. 114, 10123 (1992)] and semiempirical calculations [W. H. Shelver et al., Int. J. Quantum Chem. 44, 141 (1992)], but at the ab initio level, its computed H-bond geometrical parameters are fairly consistent with the X-ray observed ones. The relative stability of all the structures is compared in vacuo and in aqueous solution using the polarizable continuum model (PCM) of the solvent, whose stabilizing effect, however, is not sufficient to fill the large energy gap between the less lipophilic conformers and the most stable one in vacuo, in agreement with previous CD measurements. The energetic cost imposed to the solvent effect by each intramolecular H bond is almost constant if the other structural features do not change appreciably. The trend of the purely electrostatic results obtained employing a partial charge model of bilirubin is analogous to that produced by its polarized ab initio charge distribution.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 395-405, 1998
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  • 100
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 70 (1998), S. 429-440 
    ISSN: 0020-7608
    Keywords: symmetric group ; class-sums ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An algorithm for the evaluation of products of arbitrary conjugacy class-sums in the symmetric group is conjectured. This algorithm generalizes a procedure presented sometime ago, which deals with products in which at least one of the class-sums involved consists of a single cycle (and an appropriate number of fixed points). Let the support size of a conjugacy class be the number of indices that are not fixed points. The algorithm proposed implies that the coefficient of the class-sum C in the product of the class-sums A and B is given in terms of a well-defined enumeration problem within the symmetric group Sp, where p is the smallest of the support sizes of A, B, and C.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 429-440, 1998
    Type of Medium: Electronic Resource
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