Exciton surface states in molecular crystals

Abstract

A new Hamiltonian partition method, used previously for cooperative excitations in molecular crystals, has been adopted for the treatment of surface exciton states in molecular crystals. The formation of surface excitons depends on the relative magnitude of the exciton transfer integrals, J terms, as compared to the environmental shift integrals, D terms. This was established for a sample calculation on a simple cubic molecular crystal. It was found that when the absolute value of the nearest neighbor D term exceeds the corresponding J term two localized states emerge for each value of a two dimensional wavevector. The two localized states are degenerate in the limit of an infinitely thick crystal. The localization of the surface states increases with an increase in the magnitude of the D term.