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Keld L. Bak

GEOMETRICAL LINEAR RESPONSES AND DIRECTIONAL ENERGY DERIVATIVES FOR ENERGETICALLY DEGENERATE MCSCF ELECTRONIC FUNCTIONS

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For state-averaged multiconfigurational self consistent field (SA-MCSCF) wave functions, second-order geometrical response equations are derived that allow the determination of first-order configuration amplitude response for equally weighted, energetically degenerate states. The first-order response equations obtained in earlier work do not suffice to determine these particular responses parameters. To formulate such a derivation in a well defined manner, it is found that a specific linear combination of the degenerate states must be formed; this specific combination of states then defines how state energies and wave functions evolve as one passes through the surface intersection. The linear combination among the degenerate states is dependent upon the molecular distortion for which the responses are to be evaluated. Expressions for first- and second-order directional energy derivatives for these energetically degenerate wave functions are also derived. All the equations obtained are computationally tractable and expressed in terms of quantities that result from optimizing the SA-MCSCF wave functions and from solving the first- and part of the second-order geometrical response equations.

Original languageEnglish
JournalTheoretica chimica acta
Volume82
Issue1-2
Pages (from-to)7-27
Number of pages21
ISSN0040-5744
Publication statusPublished - Mar 1992

    Research areas

  • MCSCF, GEOMETRICAL RESPONSE EQUATIONS, COUPLING MATRIX-ELEMENTS, ANALYTIC GRADIENT METHODS, WAVE-FUNCTIONS, SURFACES, INTERSECTION, SYMMETRY, STATES, TERMS

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