Self-diffusion in a 2D lattice gas with lateral interactions

The self-diffusion coefficient D_S, is studied for submonolayer adsorbates on a square lattice; lateral interactions are taken into account. The theoretical framework is that of the Mori projection operator technique for a 2D interacting lattice gas with Kawasaki dynamics. The limit of small lateral interactions is considered and memory effects are taken into account up to high orders in the Mori continued fraction expansion. A formula for D_S is obtained which contains the static pair correlation function. The theory is then applied to a 2D lattice gas with nearest-neighbour attractive or repulsive interactions and the static correlations are calculated according to the mean spherical approximation. D_S is computed as a function of the coverage for different interaction strengths and the results are compared with a Kawasaki Monte Carlo simulation. At low coverages (θ ≤ 0.25), the agreement between the theory and the simulations is fairly good for a wide range of the interaction strength; at medium and high coverages a good agreement is obtained at small lateral interactions. The theoretical results given by different choices of the jump dynamics are shown and briefly discussed.