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  • Computational Chemistry and Molecular Modeling  (18)
  • 1980-1984  (18)
  • 1
    Electronic Resource
    Electronic Resource
    Generalized Racah method for the evaluation of CFP for mixed electronic configurations (1981)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 20 (1981), S. 763-774 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Racah method, proposed for the evaluation of coefficients of fractional parentage (CFP) for single shell configurations, is generalized for the cases of two and more than two shells. On the basis of the generalized Racah method, we have evaluated one-particle CFP for all states of svpμ electronic configurations. Two-particle CFP are expressed through one-particle CFP and Racah coefficients.
    Additional Material: 12 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560200316
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  • 2
    Electronic Resource
    Electronic Resource
    Computer generation and identification of carcinogenic bay regions in benzenoid hydrocarbons (1983)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 23 (1983), S. 713-722 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A computer-oriented algorithm is developed for identification and enumeration of carcinogenic bay regions in benzenoid hydrocarbons. The results are reported for geometrically planar benzenoid systems up to ten fused rings. They fully agree with those obtained in a different way by Balasubramanian et al. The advantage of the proposed method is that we can display all planar benzenoid structures and identify the carcinogenic bays in each of them.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560230240
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  • 3
    Electronic Resource
    Electronic Resource
    Molecular tight-binding method. I. Many-electron method for hole bands of molecular crystalsThis work was supported in part by the Polish Academy of Sciences within project No. MR-I.9. (1982)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 21 (1982), S. 967-991 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A method for calculating ab initio electronic excitation energies of molecular crystals, based on a many-electron tight-binding approximation, is described. The method follows Frenkel's model for excitons and allows a many-electron treatment of the band-structure problem of molecular crystals. The case of hole bands is studied in detail and various versions of the method are considered. A computational scheme is proposed, in which approximate correlation corrections to the HFR matrix equations of the one-electron LCMO method are calculated. The main effects contributing to these corrections are the effect of relaxation of a molecular ion, the effect of intramolecular electronic-correlation change, and the effect of polarization of the remaining molecules in a crystal. The method developed in the present paper is applied to calculation of the hole bands of the HCP helium crystal.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560210603
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  • 4
    Electronic Resource
    Electronic Resource
    Molecular tight-binding method. II. One- and many-electron method for excess electron bands of molecular crystalsThis work was supported in part by the Polish Academy of Sciences within project No. MR.I.9. (1982)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 21 (1982), S. 993-1001 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An ab initio method for calculating the energies of excess-electron bands in a molecular crystal is developed. These energies represent the electron affinities of a crystal. The present method employs a tight-binding approximation to describe the molecules in a crystal and a set of local functions to describe the excess electron. One- and many-electron formulations of the method are given, the latter takes into account the effect of polarization of all the molecules in the crystal by the excess electron. A scheme for approximate determination of the electronic-correlation corrections to the one-electron bands is developed and applied to calculation of the excess-electron bands in the HCP helium crystal.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560210604
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  • 5
    Electronic Resource
    Electronic Resource
    Direct calculation of lattice sums. A method to account for the crystal field effectsThis work was partly supported by the Polish Academy of Sciences within Project No. MR.I.9. (1982)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 22 (1982), S. 911-927 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A method of direct calculation of lattice sums in three-dimensional crystals is reported. The method is based on annihilation of some lowest multipole moments of the unit cell by a redefinition of the unit cell content. As a result, properties of the infinite crystal can be calculated as usual by taking a finite cluster of unit cells, but surrounded by an additional surface layer of a charge density (e.g., a layer of point charges). This charge density distribution produces the electric field approximating that one of the rest of the infinite crystal. The method proposed is easily applicable in the SCFLCAO procedure as well as in any method using a cluster representation for an infinite crystal. The validity of the infinite crystal model for a finite crystal is also discussed.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560220506
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  • 6
    Electronic Resource
    Electronic Resource
    Coupled-cluster method with optimized reference state (1984)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 26 (1984), S. 267-291 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We propose a variant of the coupled-cluster (CC) method in which spin orbitals of the reference Slater determinant are optimized in a self-consistent way. This approach is a reformulation of the Brueckner-Hartree-Fock (BHF) method used in nuclear physics and known also as the exact SCF method. We discuss the use of the reference-state determinants built of HF, natural, and Brueckner spin orbitals, with relations among them investigated in terms of the many-body perturbation theory (MBPT). It is shown that the Brueckner spin orbitals emerge as a convenient basis set in the coupled-cluster method and equations that determine these spin orbitals are found. The Brueckner spin orbitals can be calculated as eigenvectors of a certain Hermitian one-electron operator which has a form of the Hartree-Fock operator plus a “correlation potential” depending linearly on two- and three- electron cluster amplitudes. The usual decoupling scheme in the coupled-cluster method leads to a hierarchy of approximations; in the first nontrivial one the three-electron cluster amplitudes are neglected, and the two-electron ones are determined by solving Čižek's CPMET equations. We also analyze the problem of spatial, spin, and time-reversal symmertry in the CC and BHF methods. If (and only if) the reference-state determinant belongs to a one-dimensional representation of a certain symmetry subgroup of the system, the CC operator and the BHF one-electron operator are invariant with respect to this subgroup. Thus the restricted (entirely symmetry-adapted) version of the BHF method can be formulated only for the closed-shell systems. This is done for the above-mentioned approximate BHF method. We discuss also the usefulness of the BHF method in application to extended metallic systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560260827
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  • 7
    Electronic Resource
    Electronic Resource
    Automatic geometry optimization for molecules with d orbitals. III. The EHT method with electrostatic correctionsPart II: see Ref. 1. (1981)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 19 (1981), S. 585-591 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A procedure has been developed for automatic optimization of molecular structures in the EHT method with possible inclusion of electrostatic correction terms, operating with analytical formulas for the first derivative of the total energy in Cartesian coordinates in the s, p, d basis of Slater orbitals. Illustrative examples are given of optimization of the structural parameters of FeCl3, Fe2Cl6, FeCl4, FeCl4-, FeCl2, and FeCl2+ and of optimization of the reaction pathways of the dissociation of Fe2Cl6 yielding the other species of the above set. The values are in good argreement with the available experimental data; this agreement is discussed briefly in connection with the general applicability of the EHT method combined with automatic geometry optimization to theoretical study of compounds containing transition metal atoms.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560190412
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  • 8
    Electronic Resource
    Electronic Resource
    Electronic interactions of N-methyl-N-nitrosourea with DNA and its chemical modifications (1980)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 17 (1980), S. 1221-1227 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560170616
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  • 9
    Electronic Resource
    Electronic Resource
    Relativistic studies of atoms and ions with complex configurationsPresented at the Symposium on Relativistic Effects in Quantum Chemistry, Åbo Akademi, Finland, June 21-23, 1982. (1984)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 25 (1984), S. 47-55 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The method of the relativistic investigation of the energy spectra and the electronic transitions in the case of complex configurations, based on the theory of the irreducible tensorial operators and the genealogical coefficients, is described. The use of the quasispin and isospin technique in the relativistic approximation is discussed. Expressions are presented for electric multipole transition probabilities for general values of the gauge condition of electromagnetic field potential.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560250105
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  • 10
    Electronic Resource
    Electronic Resource
    Chemical reaction as a quantum transition (1984)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 26 (1984), S. 691-700 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this theory a chemical reaction is treated as a quantum transition from reactants to products. The approach leads to a Franck-Condon-like factor for the evaluation of product energy distributions. Second-quantization representation is used to enable a Hamiltonian for reaction to be defined. A specific adiabatic method is used to describe the dynamics of nuclear motion. The theory is applied to the reactions HO + D → OD + H and ClI + D → Cl + ID. Polyatomic photodissociation can also be treated by a similar formalism.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560260861
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