Local-field effects on carrier hopping mobilities

The work required to move a charge between different sites in a lattice subject to an electric field is treated in detail. It includes a local-field contribution when the sites are inequivalent and in non-centrosymmetric crystals also when the sites are equivalent (except for special field directions). The effect on carrier hopping mobilities is discussed, ignoring dynamical and polaron effects. In most cases of interest, the local field does not affect low-field mobilities significantly, but it can affect high-field mobilities. For amorphous materials, this effect is probably less important than fluctuations in the barriers to hopping.