Stochastic interpretation of the rate equation formulation of hopping transport theory. II. The DC limit

For pt. I see abstr. A32938 of 1974. The exact AC diffusivity formula derived in I reduces to D(0)=fd 2 /2 in the DC limit where f is the mean hopping frequency and d 2 is the mean square x displacement per hop in an infinite chain of hops. The mean hopping frequency is equal to a simple average of the total hopping rate out of each site. The predicted behaviour of f and d 2 contrasts strongly with that found in recent approximations to the stochastic formula in the DC limit because the approximations employed are equivalent to re-randomizing the site distribution after every hop.