Collective surface diffusion on a triangular lattice in presence of ordered phases

Diffusion is studied in a two-dimensional gas of triangular symmetry with repulsive interactions. The collective diffusion coefficient, Dc, is calculated as the ratio of the average jump rate and the zero-wave-vector static structure factor (Darken approximation). The dependence of Dc on coverage, ?, is studied in both the disordered and ordered regions of the phase diagram. It is shown that, around the coverages of the perfect ordered phases (?=1/3 and 2/3), Dc changes of orders of magnitude in tiny ? ranges.