MODEL FOR DIFFUSION ON DEFORMABLE LATTICES .2. TRACER DIFFUSION

We present results of theoretical studies of tracer diffusion in a lattice-gas model that has been proposed to explain the anomalous diffusion anisotropy of H adatoms on a W(110) surface. This study complements our previous calculations of collective diffusion within the model (Ala-Nissila et al., preceding paper). We first perform extensive Monte Carlo random-walk simulations of tracer diffusion including only the intracell hard core interactions. We then use the Green's-function method to develop an analytic mean-field theory for the tracer-diffusion coefficients. We also present a derivation of an improved solution to second order in the Green's-function expansion. The range of validity of these analytic results is examined by comparison with the simulations. Finally, we compare the properties of tracer diffusion with collective diffusion.