Self consistent field perturbation theory for Frenkel and charge transfer states of hydrogen bonded crystals

An all valence electron theory, based on SCF perturbation theory, for the excited state energies of crystals with energy bands of low to intermediate dispersion is presented. It is shown that molecular theory leads to results equivalent to those of the valence bond treatments of Davydov and Choi, Silbey, Jortner, and Rice. The advantages of the proposed MO approach are twofold. First, the explicit inclusion of all valence electrons permits an unambiguous calculation of any structural changes that may accompany electronic excitation. Second, and more important, it provides a convenient method for calculating the excited states of crystals composed of relatively strongly interacting molecules, such as those within lattices of hydrogen bonded or charge transfer crystals.