A MUTUALLY CONSISTENT PROCEDURE FOR EXCITATION-ENERGIES AND TRANSITION DENSITIES BASED ON THE EXTENDED BRILLOUINS THEOREM

A mutually consistent method to calculate excitation energies and corr esponding transition densities is proposed. The method is based on the extended Brillouin's theorem that is derived from the nonstationary v ariation principle. Within the proposed procedure, the Brillouin's con ditions, which appear in this extension, are used as a set of nonlinea r equations for molecular orbitals and configuration interaction coeff icients of the trial ground- and excited-state functions. The excitati on energy is an eigenvalue of the set. To some extent, this procedure is related to the variational treatment of the conventional random-pha se approximation within the equation-of-motion method. The basic featu res of the proposed procedure are discussed and it is illustrated by n umerical examples.