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  • 1
    Electronic Resource
    Electronic Resource
    Quantum-chemical study of the relation between electronic structure and pA2 in a series of 5-substituted tryptamines (1985)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 28 (1985), S. 421-428 
    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 have analyzed the dependence of the serotonin receptor binding affinity on the electronic and steric reactivity indexes for a group of 5-substituted tryptamines. The approaches employed are a new nonempirical Quantitative Structure - Activity relationship approach and multiple regression analyses. The results suggest that the variation of the receptor binding affinity in 5-substituted tryptamines is related to the variation of the net charge of two atoms and to the steric bulk of the N-substituent. A receptor model is proposed.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560280402
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  • 2
    Electronic Resource
    Electronic Resource
    Solution of the integral Dirac equation in momentum space (1987)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 32 (1987), S. 417-423 
    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 discuss the solution of the integral Dirac-Fock equation in momentum space. “Balanced” momentum-space gaussian functions are used to expand the large and small components of the Dirac 4-spinors. We show that this approach, which has been successfully used in atomic Dirac-Fock calculations, works equally well in molecular Dirac-Fock calculations.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560320741
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  • 3
    Electronic Resource
    Electronic Resource
    Fully numerical solutions of the hartree-fock equation in momentum space: A numerical study of the He atom and H+2 ion (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 445-456 
    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 major impediment to achieving accurate solutions of the momentum-space Hartree-Fock equation in fully numerical form lies in the error caused by the truncation of momentum space. We use a coordinate transformation, which is characterized by P = tan(α/2), thus avoiding this truncation to achieve accurate solutions of the Hartree-Fock equation. Using this approach, we have re-examined the He model problem previously analyzed by Delhalle and Defranceschi [Intern. J. Quantum Chem. Symp. 21 425 (1987)]: The kinetic, nuclear attraction and Coulomb repulsion energies of the He atom have been evaluated using both conventional spherical polar momentum coordinates, (p, θ, ϕ) and the transformed coordinates, (α,θ,ϕ) in order to compare their accuracies. We have performed a number of fully numerical calculations on the H+2 ion in order to examine the influence of the number of points in the mesh on the accuracy of the computed total electronic energy of the diatomic molecule.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340848
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  • 4
    Electronic Resource
    Electronic Resource
    Solution of the time-dependent Schrödinger equation using a continuous Fourier transform (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 107-111 
    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 discuss the solution of the time-dependent Schrödinger equation. The split operator method is used to propagate an initial wave function and the continuous Fourier transform is applied to obtain the energy eigenvalues. High resolution in the energy is obtained without line shaping techniques.s
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400813
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  • 5
    Electronic Resource
    Electronic Resource
    Correlation and pairing in C602n- ions. Superconductivity of alkali and alkaline earth compounds of C60 (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 655-665 
    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: Hopping conductivity becomes activationless (metallic) when twice the intersite coupling supercedes the reorganization energy. Consistent with this idea, activationless electron pair transfer may be considered as a condition for the appearance of superconductivity. For electron pairs the condition is slightly more complicated than for single electrons. The activation energy depends on the relative energies between ionic states and a valence bond state. The latter serves as an intermediate state, contributing to the disappearance of the activation barrier. In A3C60, that pairing occurs because the 1Ag state of the negative ions C602- and C604- is stabilized by correlation effects and is the ground state. The correlation effects are primarily due to the closeness in energy and different parity of the tlu and tlg orbitals, which are partly occupied in the negative ions, but empty in neutral C60. The small interelectronic repulsion and the polarization energy from the environment also contribute to the stability of the evenly negative ions. © 1993 John Wiley & Sons, Inc.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560480859
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  • 6
    Electronic Resource
    Electronic Resource
    Conductivity in polyacetylene. II. Ab initio and tight-binding calculations of soliton structure and reorganization energy in ordered and disordered structures (1996)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 58 (1996), S. 517-532 
    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: Alkali-doped polyacetylene is considered as an electron-transfer system. To estimate the reorganization energy due to bond-length changes when electrons are added or subtracted, we applied the (U)MP2 and CASSCF methods to small systems of the type H(CH)NH. The simple tight-binding (Hückel) model with bond-length-dependent resonance integrals has been applied to the same and larger polyenes. The bond lengths are obtained via the bond orders for the various oxidation states. The results agree very well with the ab initio results and experiments for small polyenes. Odd-N and even-N systems behave differently. In odd-N systems, a structural “soliton” exists in the neutral molecule. An electron can be added or removed without bond-length change. In even-N chains, with perfect bond alternation in the neutral molecule, the bond length changes when an electron is accepted occur over about 20 carbon atoms. The reorganization energy tends to a constant value (0.22 eV) as the chain length is increased. Soliton structure is studied as a function of out-of-plane torsional defects and it is found that an additional electron is localized primarily on a segment with an odd number of carbon atoms. In the presence of positively charged ions, electrons are attracted toward this charge and positive solitons formed at some distance from the perturbing ion. © 1996 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Semiempirical study of compounds with intramolecular O—H…O hydrogen bonds. II. Further verification of a modified MNDO method (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 15 (1994), S. 183-189 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: In the forerunner of this article, we described a MNDO modification designed for studies of compounds with intramolecular O—H…O hydrogen bonds. Here, we report the further verification of the modification by means of its application to 14 compounds not considered in its development. Comparison of the calculated structural parameters and proton transfer characteristics with available experimental or ab initio results, and with those obtained using MNDO, AM1, MNDO/H, MNDO/M, and PM3, supports the validity of the new modification for prediction of hydrogen bond characteristics. © 1994 by John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540150208
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  • 8
    Electronic Resource
    Electronic Resource
    Semiempirical study of compounds with O-H—O intramolecular hydrogen bond (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 13 (1992), S. 860-866 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Application of MNDO, AM1, PM3, MNDO/H, and MNDO/M methods to a set of compounds with intramolecular hydrogen bonds suggested that none of these methods accurately modeled the characteristics of the hydrogen bonds. Since the MNDO/H and MNDO/M methods work well for intermolecular hydrogen bonds, we followed their example and modified MNDO for intramolecular hydrogen bonds by altering the empirical core-core repulsion energy function for all pairs of atoms involved in intramolecular O-H—O bonds. The resulting modified method models the behavior of these bonds quite well, especially as regards their geometry and the barrier to proton transfer. © 1992 by John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540130710
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  • 9
    Electronic Resource
    Electronic Resource
    Semiempirical study of electronic and bonding properties of cobalt silicide clusters (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 13 (1992), S. 867-873 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The electronic structure of cobalt silicide clusters Co7Si7 and Si7Co7 was studied in comparison to that of Co19 and Si17 clusters under the scope of the MINDO/SR method. Clusters Co7Si7 and Si7Co7 represent the environment of a cobalt atom and that of a silicon atom in the cobalt monosilicide bulk, respectively. It is found that the Co—Si bond is essentially sp in character with an indirect participation (by electrostatic interaction) of the cobalt d orbitals. Our calculations show a charge transfer from silicon to the d orbitals of cobalt via sp-sp interaction with an internal sp-d hybridization. The theoretical density of states for cobalt silicide clusters are reported and compared with experimental results of surface spectroscopies. © 1992 by John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540130711
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  • 10
    Electronic Resource
    Electronic Resource
    Quantitative comparison of molecular electrostatic potential distributions from several semiempirical and ab initio wave functions (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 14 (1993), S. 922-927 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A quantitative comparative analysis of molecular electrostatic potential (MEP) distributions generated from different wave functions was carried out. Wave functions were computed by using MNDO, AMl, STO-3G, 3-21G, 4-31G, 6-31G, 4-31G*, 6-31G*, and 6-31G** methods. Ten different compounds, which include usual atoms and groups of biomolecules, such as hydroxyl, carbonyl, amine, amide, imine, double and triple bonds, and heteroaromatic rings, were studied. For each compound, MEP values in the points of a common 3-D grid were computed; thereafter, the similarity between each pair of MEP distributions generated by different methods was assessed. Similarities were measured using the Spearman rank correlation coefficient. A similarity matrix was obtained for each compound. Similarity matrices were averaged and a hierarchical cluster analysis was carried out to classify the different quantum chemical methods. In the compounds studied, the main conclusion is the negligible difference between the pattern of MEP distributions generated from all split valence basis sets (with and without polarization functions). © 1993 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540140807
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