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Equations providing the first and second derivatives of a configuration interaction (CI) energy with respect to an external parameter are provided. We assume no restriction on the form of the CI expansion built from molecular orbitals obtained in a multiconfiguration Hartree–Fock (MCHF) calculation. Also, the coupled perturbed multiconfiguration Hartree-Fock formalism is presented for a general MCHF wave function and provides the first order and second order changes of the molecular orbital expansion coefficients with respect to an external parameter.
Michel Dupuis (Fri,) studied this question.