Single-particle density of excitations and hard gaps in localized interacting systems

A one-electron density of excitations is obtained for a system of interacting electrons in the limit of strong localization. This density of excitations is constructed from the density of states and from the pair correlation function, which is obtained numerically. From the former the distribution function for the lowest and second-lowest one-electron excitations from a given site are calculated. These distributions are used in Davies' model, resulting in a small hard gap of the order of one-tenth of the Coulomb gap.