Collective diffusion of dense adsorbate at surfaces of arbitrary geometry

A convenient variational formula for collective diffusion of many particles adsorbed at lattices of arbitrary geometry is formulated. The approach allows us to find the expressions for the diffusion coeffcient for any value of the system's coverage. It is assumed that particles interact via on-site repulsion excluding double site occupancy. It is shown that the method can be applied to various systems of different geometry. Examples of real systems such as GaAs with specific energetic landscapes are also presented. Diffusion of Ga adatoms on GaAs(0 0 1) surface reconstructed in two different symmetries is studied. It is shown how increasing Ga coverage changes the character of diffusion from isotropic 2D into highly anisotropic, almost 1D. It is shown how important the role of the inter-particle correlations is, which influences the value of the collective diffusion coeffcient at higher coverages.