THE VELOCITY AUTOCORRELATION FUNCTION FOR A RANDOM-WALK ON PERCOLATION CLUSTERS

We apply the random Lorentz model to diffusion on percolation clusters on a square lattice. In this model a walker performs a random walk on cluster sites and can visit sites occupied by impurities which play t he role of reflectors. The velocity autocorrelation function and the m ean-square displacement of a random walker are calculated with high ac curacy using a moment-propagation numerical technique. Exponents descr ibing the decay of correlation function are calculated at the percolat ion threshold and above it.