Tracer diffusion of particles with soft-core interactions studied by Monte Carlo simulations

We consider, using Monte Carlo simulations, diffusion of particles on a square lattice. The particles do not interact among themselves, except that at the same lattice site there cannot be more than particles. Since the interactions in our model are a milder version of the well known hard-core (HC) lattice gas, for which , we decided to call our model the soft-core (SC) lattice gas. We find the dependence of the correlation factor on the concentration of completely filled sites and show that the correlations decrease with increasing . We calculate analytically and via the Monte Carlo simulations the distribution function of the average number of sites occupied by a given number of particles. The curves show that for our model the `particle - hole' symmetry, typical for the HC lattice gas, disappears. In addition, we have found in 1D two regimes of diffusion for . For shorter times the diffusion is anomalous, while for longer times it becomes normal.