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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 73 (1988), S. 383-391 
    ISSN: 1432-2234
    Keywords: Alternant molecular orbital method ; Paired orbital method ; Electron correlation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The energy expression and its derivatives have been derived in the paired orbital (PO) method. Several relations have been derived for the values of the basic functions at the Hartree-Fock limit. These relations permit to draw conclusions about the behavior of the energy expression as a function of the nonlinear parameters around this limit point and it shows that one can expect an improvement in energy as compared to the Hartree-Fock value using the nonlinear parameters as variational parameters.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 62 (1997), S. 245-259 
    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: An efficient expansion method for the evaluation of VB matrix elements is introduced. The overlaps of VB wave functions of N electrons can be treated as algebrants, i.e., generalized determinants, of N × N matrices. An algebrant can be expanded with subalgebrants of lower orders in a successive way. By choosing Rumer spin bases and appropriately arranging the expansion, it is found that the number of unique subalgebrants involved in the expansion increases in a quite moderate way with N. In contrast to the traditional symmetric group approach, which explicitly utilizes all N! representation matrices, the new strategy incorporates the group theoretical factors in a simple way in the successive expansion. As only the unique subalgebrants are further expanded, the computational effort required by the new strategy scales in a very acceptable manner with the increasing number of electrons. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 62: 245-259, 1997
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
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  • 3
    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: L'emploi de fonctions de spin différentes dans la méthode AMO est étudié pour le benzéne, l'anneau de six atomes H, et le fulvéne. L'amélioration additionnelle obtenue par l'emploi d'une combinaison linéaire de fonctions de spin différentes est trés petite pour l'état fondamental singulet. On montre l'existence d'importantes différences d'énergie entre des fonctions ayant la měme dépendance spatiale mais caractérisées par des fonctions de spin différentes.
    Abstract: Anwendung verschiedener Spin Funktionen wurde im Rahmen der AMO Methode für Benzol, den Ring von sechs Hatomen, und Fulven untersucht. Die Verbesserung der Energie, die durch die Anwendung linearer Kombinationen verschiedener Spin Funktionen erhalten wird, ist in dem Singulet Grundzustand klein. Es wurde gezeigt, dass man grosse Differenzen in Energie feststellt für Funktionen, die dieselbe Raum-Funktion aber verschiedene Spin Funktionen haben.
    Notes: The use of different spin functions in the AMO method was investigated for benzene, the ring of six H atoms, and fulvene. The additional improvement in the energy obtained by the use of a linear combination of different spin functions is quite small for the singlet ground state. It is pointed out that there are great differences in energy between functions having the same spatial function but different spin functions.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 41 (1992), S. 147-151 
    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: Explicit expressions for the eigenvalues of the class sums [(p)(1)n-p]n, p = 2, 3,…,14, of the symmetric group Sn are presented. Partial results are given for the eigenvalues corresponding to arbitrary p.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 25 (1984), S. 707-713 
    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 new derivation is given for the Waller-Hartree-Fock double-determinantal spatial wave function. One starts from the single-determinant wave function in which a orbitals are doubly occupied, and decomposes it into a sum of products of spatial and spin functions. The spatial product of the first genealogical spin eigenfunction is a double-determinantal function. The derivation is based on the simple form of U1ƒ(P) when the representation matrix is obtained from the genealogical spin eigenfunction.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 36 (1989), S. 669-670 
    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
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 125-134 
    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: Explicit expressions for the eigenvalues of the single-cycle class-sums [(p)(1)n-p]n of the symmetric group (Sn), with p ≤ 20, are constructed. A new algorithm is used that makes no use of representation-theoretic data. The expressions obtained consist of polynomials in the symmetric power-sums over the “contents” of the Young diagram specifying the irreducible representation, with coefficients that are polynomials in n. On the basis of the results obtained for p ≤ 20, a conjecture is proposed concerning the general form of the four leading terms in these polynomials. © 1993 John Wiley & Sons, Inc.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 12 (1977), S. 369-382 
    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: Branching diagram and Serber-type spin functions are ordered according to their diagrams. The method of Graebenstetter et al. is slightly modified; it provides an effective algorithm for the construction of genealogical spin functions. A counterpart of the method is developed for Serber-type spin functions. Special properties of branching diagram functions and Serber-functions are established.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 35 (1989), S. 717-719 
    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
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 37 (1990), S. 509-516 
    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: The purpose of this article is the comparison of generalized valence bond (GVB) and the alternant molecular orbital (AMO) techniques both in the localized and delocalized form. The model we have chosen is the PPP model of cis-butadiene which is relatively simple and transparent. For equal bond lengths the AMO using delocalized orbitals is better than the GVB. For physical distances of the atoms these methods are of comparable accuracy. With the extension of the length of the central bond the GVB becomes better and is exact in the limit of two ethylenes. The AMO method using localized orbitals always gives the worst result of the three. In the limit of two ethylenes AMO in the localized and delocalized forms give the same error.
    Additional Material: 7 Tab.
    Type of Medium: Electronic Resource
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