Chemical surface diffusion with long jumps

A model for the diffusion of particles in a two-dimensional Langmuir gas, which considers the possibility of long jumps, is proposed. The model is of interest for surface diffusion in adsorbed layers and it is solved by the Mori projection operator technique. The chemical (or collective) diffusion coefficient Dc is calculated in the dynamical mean-field approximation, neglecting memory effects. It is shown that long jumps induce a coverage dependence in Dc, which is absent when only single jumps are taken into account.