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  • 1
    Electronic Resource
    Electronic Resource
    A generalization of the AGP model propagator to a reference state including different geminals (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 4187-4193 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A geminal product (GP) of two different geminals g'(1,2)g''(3,4) is compared to other GP's of type g(1,2)g(3,4) and u(1)u(2)g(3,4) in an application to the ground state of Be. The factorization g'g'' is remarkable since it gives, within the basis sets employed, the same total energy as a multiconfigurational self consistent field (MCSCF) calculation using the same configurations. A model wave function is chosen as an antisymmetrized product of an independent particle function and a correlated four-electron part. The latter consists of a multiconfigurational expansion restricted to pair substitutions of which the product of different geminals is a special case. We construct excitation operators that satisfy certain vacuum conditions for this reference state. In the case of four electrons this leads to a model propagator which is a direct generalization of a recently reported model propagator based on an antisymmetrized geminal power (AGP) reference state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.448860
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  • 2
    Electronic Resource
    Electronic Resource
    Study of mode specificity by the natural expansion analysis (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 3924-3931 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The self-consistent field (SCF) method beyond its computational advantage lends meaning to the concept of local modes and its applicability implies mode specificity in the unimolecular reaction being studied. The natural expansion (NE) analysis of stable or metastable vibrational states is presented here first. The NE analysis enables us to determine the applicability of the SCF approximation, the optimal molecular modes for any given vibrational energy and therefore provides a positive test for mode specificity. Moreover, it is shown here that even when the internal coordinates of the Hamiltonian are not optimized and there are several dominant configurations in the NE, mode specificity can be indicated by analyzing these configurations. As examples, the mode specificity in the unimolecular decomposition of CO2 to CO+O and in the dissociation of formaldehyde to H2+CO are studied by the NE analysis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449104
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  • 3
    Electronic Resource
    Electronic Resource
    Resonances from the complex dilated Hamiltonians in a dilation-adapted basis set with a new stabilization parameter (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 3931-3936 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Explicit consideration of the analytic properties of the solutions to the dilated Hamiltonian is taken into account in the construction of the matrix representation of the latter in an L2 basis. The total dilated matrix is blocked according to division of the basis into "bound'' and "scattering'' subspaces, which are interacting via the off-diagonal blocks, leading to a coupling maintaining the adequacy of the bound part of the basis throughout the wide range of the dilation angle. The size of the bound subspace, M, becomes a new stabilization parameter; its variation covers the entire range of situations between a real stabilization calculation and the conventional complex-scaling calculation. This construction allows for a systematic analysis of the dilated Hamiltonian, bringing forward the physical interpretation of the configuration interaction while suppressing the disadvantageous effects of the dilation transformation, manifested by poor convergence. The connections to Junker's complex stabilization method are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450103
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  • 4
    Electronic Resource
    Electronic Resource
    Charge-transfer processes in bipyrazine and bi-(N-methylpyridine): A semiempirical MO study (1992)
    Springer
    Molecular engineering 2 (1992), S. 1-16 
    Details
    ISSN: 1572-8951
    Keywords: Charge transfer ; bipyrazine ; bi-(N-methylpyridine) ; localized excitations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In the present paper, the bipyrazine and bi-(N-methylpyridine) dication systems are studied. Charge distributions and occupied and unoccupied molecular orbitals, obtained from semiempirical MNDO calculations, are reported as functions of the length of the π-chain connecting the pyrazine/pyridine fragments. Single CI calculations, using ZINDO, are performed, and the transition energies and oscillator strengths for various vertical excitations from the ground state, along with the excited state dipole moments, are reported. The concepts of broken symmetry and localized excitations, to enhance the charge transfer in this class of compounds, are discussed. Comparison with theoretical and experimental studies of core photoionization and valence-excitation in nitrogen-containing molecules is made.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00999518
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  • 5
    Electronic Resource
    Electronic Resource
    Symmetry breaking in charge-transfer compounds. The effects of electric fields and substituents on the properties of bipyrazine cations (1995)
    Springer
    Molecular engineering 4 (1995), S. 339-352 
    Details
    ISSN: 1572-8951
    Keywords: Symmetry breaking ; charge transfer ; effect of electric field ; bipyrazine cathris
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The effects of an electric field and of various substituents on the symmetry breaking of degenerate near-midgap orbitals and on different properties in bi-N,N′-pyrazine-1,6-hexatriene dications ([C4N2H4—(CH)6—C4N2H4]2+) are investigated by means of semiempirical PM3 and INDO CI methods. The electric field is simulated by applying positive/negative point charges at varying distances from the end-points, and the substitutions are done with single chlorine atoms or with CN, OH or CH3 groups, at various positions along the chain or on one of the pyrazine rings. The results are compared with calculations on the unsubstituted, field-free system. It is found that an electric field (e.g., as applied over a membrane) leads to significant symmetry breaking and also polarizes the HOMO and LUMO, such that electron transfer between these orbitals generates large dipole-moment shifts and non-negligible oscillator strengths. With substituents, no major symmetry breaking is observed for the ground state. Instead, strong modifications of the orbital picture are observed, in particular when using the stronger electron-withdrawing substituents. Placing the substituent in a ring position does, furthermore, lead to the possibility of large charge transfer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01019467
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  • 6
    Electronic Resource
    Electronic Resource
    Upper and lower bounds to polarizabilities and van der Waals forces I. General theory (1968)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 2 (1968), S. 761-784 
    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
    Description / Table of Contents: Des bornes supérieures et inférieures pour les polarisabilités et pour les interactions à longue distance des atomes et des molécules sont déduites en usant des inégalités pour opérateurs.Les formules pour les forces de dispersion et les forces non-additives à trois corps, sont données en termes des S(k) rapportés, par régles de somme, avec des propriétés des systèmes séparés.Quelques approximations déjà connues sont obtenues, mais avec information additionelle sur leur nature, ainsi que plusieurs inégalités nouvelles. Leur intérět est qu'elles donnent des bornes explicites et rigoureuses renfermant des quantités accessibles à partir des données experimentales.
    Abstract: Obere und untere Grenzen für die Polarisierbarkeiten und für die “long-range” Wechselwirkungen zwischen Atomen und Molekülen wurden mittels Operatorungleichungen hergeleitet. Die Formeln für die Dispersionskräfte und die nichtadditiven Dreikörperkräfte sind in den S(k), die durch Summenregeln mit den Eigenschaften der getrennten Systeme in Verbindung stehen, ausgedrückt.Einige schon bekannte Annäherungen wurden erhalten, aber mit zusätzlicher Information über ihre Beschaffenheit. Mehrere neuen Ungleichungen wurden hergeleitet, die explizite und strenge Grenzen geben, welche in solchen Grössen ausgedrückt sind, die aus experimentellen Tatsachen berechnet werden können.
    Notes: Upper and lower bounds to polarizabilities, and long-range interactions of atoms and molecules are derived using operator inequalities.The formulae for the dispersion and the three-body non-additive forces are given in terms of the S(k), related by sum rules to properties of the separated systems.Some known approximations are obtained but with additional information about their nature, as well as several new inequalities. Their interest is that they give explicit and rigorous bounds involving quantities available from experimental data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560020604
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  • 7
    Electronic Resource
    Electronic Resource
    Principles of Ultraviolet Photoelectron Spectroscopy. J. W. Rabalais. Wiley-Interscience Monographs in Chemical Physics, New York, 1977. Price: $22.50. (1978)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 13 (1978), S. 263-263 
    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
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560130213
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  • 8
    Electronic Resource
    Electronic Resource
    Self-consistent approximation to the polarization propagator (1980)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 18 (1980), S. 1109-1131 
    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 theorem is presented that characterizes approximate states and truncated operator manifolds associated with self-consistent approximate propagators. This theorem establishes a natural relationship between Hermiticity, stationarity, nonredundance and completeness of operator manifolds, model time evolution, and the vacuum condition. For the case of the polarization propagator we describe algorithms by which we can construct states and manifolds that satisfy this theorem and the vacuum condition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560180417
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  • 9
    Electronic Resource
    Electronic Resource
    Preface (1983)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 23 (1983), S. v 
    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
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560230102
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  • 10
    Electronic Resource
    Electronic Resource
    Introduction (1987)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 31 (1987), S. 697-697 
    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
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560310502
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