Tracer, jump, and chemical diffusion coefficients D*, Dj, and D, respectively, were determined on a 50 x 50 square array of fixed sites by the fluctuation and Kubo-Green methods for the case of nearest-neighbor repulsions and numerically equal next-nearest-neighbor attractions. Both methods give the same D values except at θ = 0.5 and T/Tc < 0.9, where c(2x2) dominates and simulations were extremely sensitive to very small changes in the small amount of disorder. Activation energies are, in all cases, controlled by next-nearest-neighbor attraction, i.e., were positive relative to the non-interacting case and peak at θ = 0.5. However, D had a maximum at θ = 0.5 because of a deep minimum in <(δN)2>/<N>. D* and Dj were very similar to each other and had a minimum at θ = 0.5 and low T, because of the maxima in activation energies at this coverage, caused by the necessity to deform the c(2x2) structure.

A Monte Carlo Study of Surface Diffusion Coefficients in the Presence of Adsorbate-Adsorbate Interactions. III. Repulsive Nearest-Neighbor and Attractive Next-Nearest-Neighbor Interactions. C.Uebing, R.Gomer: The Journal of Chemical Physics, 1991, 95[10], 7641-7