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  • 1
    Digitale Medien
    Digitale Medien
    Modern valence bond representations of CASSCF wavefunctions (1996)
    Springer
    Theoretical chemistry accounts 93 (1996), S. 343-366 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF01129215
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  • 2
    Digitale Medien
    Digitale Medien
    Exact transformations of CI spaces, VB representations of CASSCF wavefunctions and the optimization of VB wavefunctions (1996)
    Springer
    Theoretical chemistry accounts 94 (1996), S. 233-245 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF00186445
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  • 3
    Digitale Medien
    Digitale Medien
    Symmetry adaptation and the utilization of point group symmetry in valence bond calculations, including CASVB (1997)
    Springer
    Theoretical chemistry accounts 95 (1997), S. 131-150 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF02341697
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  • 4
    Digitale Medien
    Digitale Medien
    A New Approach to Valence Bond Calculations: CASVB (1997)
    Springer
    Molecular engineering 7 (1997), S. 67-85 
    Details
    ISSN: 1572-8951
    Schlagwort(e): Valence-bond wavefunctions ; non-unitary orbital transformations ; CASVB
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract We present a new approach to the fully-variational optimization of general types of valence-bond wavefunction. Analogous techniques may be used to generate modern valence-bond representations of CASSCF structure spaces. These various procedures, which we term CASVB, are made possible by a highly efficient algorithm for performing exactly the transformations of full CI spaces that arise from general, non-unitary orbital transformations. As examples, we consider modern valence-bond representations of 'N in N' CASSCF descriptions of methane and diborane, in which the total wavefunction is dominated by covalent structures built from a common product of N nonorthogonal orbitals. These two cases highlight some of the possible differences that may arise between representations of CASSCF wavefunctions and the corresponding fully-variational valence bond results.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1008270112260
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  • 5
    Digitale Medien
    Digitale Medien
    Expansion of the spin-coupled wavefunction in Slater determinants (1993)
    Springer
    Theoretical chemistry accounts 85 (1993), S. 261-270 
    Details
    ISSN: 1432-2234
    Schlagwort(e): Spin-coupled wavefunction ; Slater determinants ; Nonorthogonal spin-orbitals
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary The expansion of the spin-coupled wavefunction in Slater determinants constructed from nonorthogonal spin-orbitals is discussed. It proves possible to generate from cofactors of the appropriate overlap matrix all the density matrices, up to fourth order, required for the variational optimization of the wavefunction. The computational effort inherent in this ‘super-cofactor’ strategy scales in a very acceptable manner with the number of electrons.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01129116
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  • 6
    Digitale Medien
    Digitale Medien
    Nonorthogonal weights of modern VB wavefunctions. Implementation and applications within CASVB (1998)
    Springer
    Journal of mathematical chemistry 23 (1998), S. 105-106 
    Details
    ISSN: 1572-8897
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Mathematik
    Notizen: Abstract The CASVB approach is a recent development in modern valence bond theory which aims to provide easily visualized, highly accurate representations of very general types of CASSCF wavefunctions. Fully variational optimization may also be performed for quite general types of modern valence bond wavefunction. Numerous definitions of nonorthogonal weights are used to investigate the role of contributions from various types of ‘ionic’ configurations, taking hexatriene and N2S2 as illustrative examples.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1019100703879
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  • 7
    Digitale Medien
    Digitale Medien
    Modern valence bond representations of CASSCF wavefunctions (1996)
    Springer
    Theoretica chimica acta 93 (1996), S. 343-366 
    Details
    ISSN: 0040-5744
    Schlagwort(e): Key words: CASSCF ; Spin-coupled ; VB ; CASVB
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract.  Exact transformations of “N electrons in N 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 of nonorthogonal orbitals. The resulting descriptions of the electronic structure may be compared directly with those that arise in the spin-coupled (or full-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 in N” CASSCF wavefunctions, which we denote CASVB.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01129215
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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    Artikel (Nationallizenzen)
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  • 8
    Digitale Medien
    Digitale Medien
    Exact transformations of CI spaces, VB representations of CASSCF wavefunctions and the optimization of VB wavefunctions (1996)
    Springer
    Theoretica chimica acta 94 (1996), S. 233-245 
    Details
    ISSN: 0040-5744
    Schlagwort(e): Key words: 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
    URL: http://dx.doi.org/10.1007/BF00186445
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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    Artikel (Nationallizenzen)
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  • 9
    Digitale Medien
    Digitale Medien
    Symmetry adaptation and the utilization of point group symmetry in valence bond calculations, including CASVB (1997)
    Springer
    Theoretica chimica acta 95 (1997), S. 131-150 
    Details
    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
    URL: http://dx.doi.org/10.1007/s002140050189
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  • 10
    Digitale Medien
    Digitale Medien
    Fully variational optimization of modern VB wave functions using the CASVB strategy (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 65 (1997), S. 439-451 
    Details
    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
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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