The asymmetrical next-nearest neighbor Ising model was used to describe the self-diffusion of adsorbate atoms at low temperature, furthermore adding a relevant ingredient in such a regime, i.e., a finite value Q for the trapping potential barrier. The Monte Carlo technique led to the components of the (tracer) diffusion coefficient. An interesting feature was seen: a "V-A. transition" occurred at half-coverage (c = 0.5) when the temperature was lowered. The activation energy (obtained from an Arrhenius plot) was seen to be varying as a function of coverage, and was not symmetrical with respect to c = 0.5. The anisotropy of the diffusion and the change in its pattern as a function of the temperature and coverage were presented and discussed. Monte Carlo snapshots were shown at various coverage and temperature values.

Monte Carlo Investigation of Surface Self-Diffusion: the Role of Anisotropic Next-Nearest Neighbor Interactions. A.Pekalski, M.Ausloos: The Journal of Chemical Physics, 1994, 100[4], 3175-80