Abstract
A class of electron models which reduce to a superposition of nonorthogonal determinants is studied by methods of covariant quantum chemistry. A compact matrix representation is found which contains variational parameters only in the form of Fock-Dirac densities ρA, ρb of separate determinants ¦φ>,...,¦φB>. Nonorthogonality of the determinants is taken into account by means of additional projectors obtained by pseudo-inversion of the products of the form ρAρB-Orbital optimization is thus reduced to a clearly Hermitian eigenvalue problem. Inclusion in the initial model of configurations singly excited with respect to each of the determinants ¦φa> ...,¦φB> is discussed. This generalized Tamm-Dancoff model is studied in detail for the spin-symmetrized (half-projected) Hartree-Fock methods. Correlation effects in the excited states of model π-systems of the alternant type are analyzed within the framework of the model.
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Translated from Teoreticheskaya i Éksperimentalnaya Khimiya, Vol. 22, No. 5, pp. 513–523, September–October, 1986.
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Luzanov, A.V. Configuration interaction in a nonorthogonal determinant basis. Theor Exp Chem 22, 489–499 (1987). https://doi.org/10.1007/BF00522533
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DOI: https://doi.org/10.1007/BF00522533