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  • 1
    Digitale Medien
    Digitale Medien
    Springer
    Theoretical chemistry accounts 93 (1996), S. 343-366 
    ISSN: 1432-2234
    Schlagwort(e): CASSCF ; Spin-coupled ; VB ; CASVB
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Exact transformations of “N electrons inN orbitals” CASSCF structure spaces are examined that lead to modern valence bond representations, in which the total wavefunction is dominated by covalent structures built from a common product ofnonorthogonal orbitals. The resulting descriptions of the electronic structure may be compared directly with those that arise in the spin-coupled (orfull-GVB) approach. Using singlet methylene, methane and ozone as representative examples, various overlap-based and energy-based criteria are investigated for generating modern VB representations of “N inN” CASSCF wavefunctions, which we denote CASVB.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    Theoretical chemistry accounts 94 (1996), S. 233-245 
    ISSN: 1432-2234
    Schlagwort(e): CASSCF ; VB ; Orbital optimization
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary It is demonstrated how exact transformations of full CI spaces may be carried out for general, non-unitary orbital transformations, and a detailed description of an efficient implementation of this scheme is presented for Slater determinants. It is then shown how this technology may be employed in the optimization of general VB wave functions with respect to both orbital and structure coefficients. This may be done in a straightforward manner, incorporating first and second derivatives of the variational parameters.
    Materialart: Digitale Medien
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  • 3
    ISSN: 1432-2234
    Schlagwort(e): CASVB ; CASSCF ; VB ; Symmetry adaptation ; Spin-coupled
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract We present practical approaches for symmetry-adapting valence bond wave functions, with emphasis on the CASVB method. Significant savings in the computational effort become available, both in relation to the application of the Hamiltonian operator and to the reduced number of variational parameters. Results are presented for modern VB representations of CASSCF descriptions of benzene and diborane.
    Materialart: Digitale Medien
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  • 4
    ISSN: 0040-5744
    Schlagwort(e): Key words: CASVB ; CASSCF ; VB ; Symmetry adaptation ; Spin-coupled
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract.  We present practical approaches for symmetry-adapting valence bond wave functions, with emphasis on the CASVB method. Significant savings in the computational effort become available, both in relation to the application of the Hamiltonian operator and to the reduced number of variational parameters. Results are presented for modern VB representations of CASSCF descriptions of benzene and diborane.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 65 (1997), S. 439-451 
    ISSN: 0020-7608
    Schlagwort(e): CASVB ; modern VB ; nonorthogonal orbital optimization ; multiconfiguration spin-coupled ; CASSCF ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: We outline the CASVB strategy, which may be used either to generate very compact modern valence bond representations of CASSCF wave functions or to optimize general types of modern VB wave function. A simple algorithm is presented for the elimination of redundant or constrained parameters from the appropriate second-order optimization problems. Selected results for three systems - benzene, the allyl radical, and LiH - are used to illustrate various ways in which CASVB procedures can be used to perform fully variational optimizations of nonorthogonal orbitals and structure coefficients in modern VB wave functions.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 65: 439-451, 1997
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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