Theory of electronic transport in molecular crystals. III. Diffusion coefficient incorporating nonlocal linear electron–phonon coupling

Abstract

Electronic transport in molecular crystals is studied for simultaneous local and nonlocal linear electron–phonon coupling using a generalized polaron Hamiltonian derived previously. Nonlocal coupling increases the scattering, giving lower band contributions and higher hopping contributions. It also gives a phonon-assisted term which dominates at high temperature, leading eventually to a constant diffusion coefficient whose magnitude depends on the ratio of the nonlocal to local coupling and is independent of transfer integral. Incorporating nonlocal coupling thus mainly increases the magnitude of the difffusion coefficient and decreases its temperature dependence.