OVERDAMPED DIFFUSION IN COUPLED POTENTIALS

An analytical ''quasi-2D'' approximation (Q2DA) for the diffusion coef ficient of an adatom migrating in a rectangular lattice, in the presen ce of a high damping and of a general 2D-coupled potential, is derived . The validity of the Q2DA lies on the assumption that all the most re levant diffusion paths can be treated as straight lines. That is the c ase of the square 2D-coupled egg-carton potential, where the Q2DA is a pplied. Comparison with the exact numerical results (2D Smoluchowski e quation) shows that the Q2DA provides a very good approximation of the diffusion constant even in the strongest coupling situations.