Collective and tracer diffusion in low-coverage adsorbates

In the present paper both the self (or tracer) diffusion coefficient D_s and the chemical (or collective) diffusion coefficient D_c are computed for the Ising-Peierls lattice gas with nearest-neighbour interactions as functions of coverage θ. The two quantities are calculated in the framework of the Mori projection-operator formalism. Here D_s and D_c are studied for coverages up to 1 4 and memory effects are neglected. It turns out that at low lateral coupling D_s depends on coverage more strongly than D_c. The collective diffusion coefficient is more sensitive to the increase oflateral interactions than the self diffusion coefficient. In the range of coverages under investigation, D_c is an increasing function of θ in the repulsive case, whereas, if attractive interactions are present, it decreases as θ increases. The theoretical results given by different choices of the jump dynamics are shown and briefly discussed.