Adsorption and diffusion of repulsively interacting particles on a triangular lattice

We analyze the collective surface diffusion behavior of atoms adsorbed on a two-dimensional lattice-gas model with triangular symmetry in the presence of a second order phase transition. For this purpose we have studied several physical quantities which are required in the description of diffusion. The average energy per adsorbed particle, the mean square coverage fluctuations and jump diffusion coefficient have been evaluated by using the real space renormalization group (RSRG) and the Monte Carlo (MC) method. We have also calculated the tracer diffusion coefficient as well as the tracer correlation factor by MC simulations. It is shown that the precision of the RSRG technique depends not only on the number of sites in the block but also on its symmetry. The most accurate results have been obtained for the comparatively small cluster used in the present work containing 21 lattice sites. Despite the fact that both methods, RSRG and MC, constitute very different approaches, the correspondence of the numerical data is surprisingly good. It is also shown that drastic changes in the surface diffusion coefficients occur when the lateral interactions force ordering of the adatoms ia a second order phase transition.