Site representation for charge transfer excitations in molecular crystals

Abstract

A phenomenological site hamiltonian is constructed for molecular crystals whose lowest electronic excitations involve an electron transfer, as in many donor-acceptor and free-radical crystals. When only the lowest chargetransfer states are retained, a fermion representation of the site hamiltonian is obtained which leads to a typical many-body problem. The model reduces in special cases to the Hubbard and the Pariser-Parr-Pople models. However, instead of a one-electron, frozen core model, the site representation includes core rearrangements and polarization.