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  • 1
    Digitale Medien
    Digitale Medien
    s.l. : American Chemical Society
    Journal of the American Chemical Society 96 (1974), S. 5959-5967 
    ISSN: 1520-5126
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    s.l. : American Chemical Society
    Journal of the American Chemical Society 97 (1975), S. 2645-2654 
    ISSN: 1520-5126
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 5847-5849 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Projection operators are used to formulate Lipkin's modified Hamiltonian. By projecting from independent quasiparticle states, a convenient general nondegenerate many-body perturbation theory is generated. A unique feature is that the final results satisfy conservation principles. Practical consequences include ordinary diagrammatic expansions and equations-of-motion for treatments of alternant molecular orbital wave functions.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    Springer
    Theoretical chemistry accounts 84 (1992), S. 1-19 
    ISSN: 1432-2234
    Schlagwort(e): 31.10.+z ; 71.10.+x ; 31.15.+q ; Perturbation theory ; Quasiparticles ; Feynman diagrams
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Many-body perturbation theory is derived for chemical bonds. Paired quasiparticles represent the bonds. Products of the paired quasiparticles define a model Bardeen-Cooper-Schrieffer function. The pairing force is added as a model interaction to the self-consistent problem. The starting model is based on valency and adiabatic symmetry correlation. Symmetries are enforced by the model Hamiltonian. Perturbative corrections are expressed as ordinary Feynman diagrams. The number of diagrams needed is the same as for particle-hole theory.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    Springer
    Theoretical chemistry accounts 84 (1992), S. 37-53 
    ISSN: 1432-2234
    Schlagwort(e): Perturbative methods ; Perturbative analysis curves ; H2 ; LiH ; FH ; F2 ; Single bonds
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A new perturbative procedure is analyzed numerically for four single bonded diatomic molecules. The starting model is the second-quantized self-consistent Heitler-London model. The unperturbed function is a four-determinant Bardeen-Cooper-Schrieffer function. The model Hamiltonian is the ordinary Hamiltonian plus linear and quadratic powers of a two-level number operator. Parameters which multiply the additional terms are chosen to enforce particle-number symmetry. Convergence of the perturbative series for the energy as a function of internuclear distance is reasonable: third-order corrections are about an order of magnitude smaller than second-order corrections; total corrections through third order are about two orders of magnitude smaller than first-order energies.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    Springer
    Theoretical chemistry accounts 84 (1992), S. 21-35 
    ISSN: 1432-2234
    Schlagwort(e): 31.10.+z ; 71.10.+x ; 31.15.+q ; Perturbative methods ; Potential energy curves ; H2 ; LiH ; FH ; F2 ; Single bonds
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A new perturbative method is applied to single bonds. The starting model is the second-quantized self-consistent Heitler-London model. The unperturbed function is a four-determinant Bardeen-Cooper-Schrieffer function. Perturbative corrections are computed with renormalized Feynman diagrams. Convergence is satisfactory by third order. Calculated (experimental) dissociation energies in eV are 4.61 (4.75) for H2, 2.37 (2.52) for LiH, 6.22 (6.13) for FH, and 1.88 (1.66) for F2. Calculated (experimental) equilibrium bond distances in Å are 0.739 (0.741) for H2, 1.598 (1.596) for LiH, 0.903 (0.917) for FH, and 1.395 (1.412) for F2. Calculated (experimental) vibrational frequencies in cm−1 are 4578 (4401) for H2, 1396 (1406) for LiH, 4447 (4138) for FH, and 927 (916) for F2. Other spectroscopic constants agree with experiment to within 11% except for anharmonicities which differ from experiment by up to 20%.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    Digitale Medien
    Digitale Medien
    Springer
    Theoretical chemistry accounts 54 (1979), S. 83-91 
    ISSN: 1432-2234
    Schlagwort(e): Higher-order excitations, contribution of ∼ to correlation energies ; Water molecule
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Using the results of a configuration interaction calculation reported by Rosenberg and Shavitt, we derive an approximation to the correlation energy which may be associated with the sum to infinite order of all linked diagrams involving singly- and doubly-excited states. This result is compared with that obtained by calculation of the energy through third-order. The fourth-order linked diagrams involving quadruply-excited states are computed. It is shown that there is a considerable degree of cancellation between the fourth-order linked diagram energy terms involving doubly-excited intermediate states only and those which contain quadruply-excited states.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
    Digitale Medien
    Digitale Medien
    Springer
    Theoretical chemistry accounts 54 (1979), S. 83-91 
    ISSN: 1432-2234
    Schlagwort(e): Higher-order excitations, contribution of ∼ to correlation energies ; Water molecule
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Using the results of a configuration interaction calculation reported by Rosenberg and Shavitt, we derive an approximation to the correlation energy which may be associated with the sum to infinite order of all linked diagrams involving singly- and doubly-excited states. This result is compared with that obtained by calculation of the energy through third-order. The fourth-order linked diagrams involving quadruply-excited states are computed. It is shown that there is a considerable degree of cancellation between the fourth-order linked diagram energy terms involving doubly-excited intermediate states only and those which contain quadruply-excited states.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 9
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 5 (1971), S. 505-512 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The various multicenter exchange, hybrid and Coulomb electron repulsion integrals that occur in molecular quantum mechanics are shown to satisfy a Poisson equation in which an overlap integral plays the role of a source distribution function. Two-, three-and four-center exchange integrals arise from four-center source functions; two- and three-center hybrid integrals arise from three-center distributions; and one- and two-center Coulomb integrals have two-center sources.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 10
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 10 (1976), S. 185-186 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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