Collective and tracer diffusion in low-coverage adsorbates

In the present paper both the self (or tracer) diffusion coefficient Ds and the chemical (or collective) diffusion coefficient Dc are computed for the Ising-Peierls lattice gas with nearest-neighbour interactions as functions of coverage ?. The two quantities are calculated in the framework of the Mori projection-operator formalism. Here Ds and Dc are studied for coverages up to and memory effects are neglected. It turns out that at low lateral coupling Ds depends on coverage more strongly than Dc. The collective diffusion coefficient is more sensitive to the increase oflateral interactions than the self diffusion coefficient. In the range of coverages under investigation, Dc is an increasing function of ? in the repulsive case, whereas, if attractive interactions are present, it decreases as ? increases. The theoretical results given by different choices of the jump dynamics are shown and briefly discussed.