A KINETIC LATTICE-GAS MODEL FOR THE TRIANGULAR LATTICE WITH STRONG DYNAMIC CORRELATIONS .1. SELF-DIFFUSION

Self-diffusion in a lattice-gas model with two-vacancy assisted hoppin g on the triangular lattice is investigated, by both Monte Carlo simul ation and analytical calculation. A very rapid decrease of the tracer- correlation factor and marked size effects in finite lattices give evi dence for strong dynamic correlations in both space and time at high p article concentration. Although the decrease of the self-diffusion coe fficient over 3.5 decades for concentrations up to c = 0.77 is best fi tted by a power law (0.835 - c)(3.54), it is argued that the model doe s not have a sharp dynamical phase transition with a critical concentr ation lower than one. The argument is based on a proof of absence of p ermanently blocked particles in infinite lattices at all concentration s below one. The self-diffusion coefficient is calculated analytically within a pair approximation which gives good results for lower concen trations, but fails at the higher concentrations. The approximation is in qualitative agreement with the Monte Carlo data for the tracer-cor relation factor at all concentrations for a variant of the model with one-vacancy assisted hopping, in which the dynamic correlations are le ss pronounced.