COLLECTIVE DIFFUSION OF LATTICE GASES IN DISORDERED LATTICES IN THE ABSENCE OF A SINGLE-PARTICLE DIFFUSION-COEFFICIENT

Collective diffusion of particles is studied in a three-dimensional la ttice-gas model with site-energy disorder. The distribution of the sit e energies is exponential, and the diffusion coefficient of independen t particles may vanish. It is demonstrated by numerical simulations th at a coefficient of collective diffusion exists, An estimate of the di ffusion coefficient for smaller particle concentrations suggests a pow er-law dependence on concentration, consistent with the simulations. A n effective-medium calculation of the coefficient of collective diffus ion gives good agreement with the data at smaller particle concentrati ons and rough agreement at larger concentrations.