Role of entropy barriers for diffusion in the periodic potential

Diffusion of a particle in the N-dimensional external potential which is periodic in one dimension and unbounded in the other N-1 dimensions is investigated. We find an analytical expression for the overdamped diffusion and study numerically the cases of moderate and low damping. We show that in the underdamped limit, the multidimensional effects lead to a reduction (compared to the one-dimensional motion) in the jump lengths between subsequent trappings of the atom at the minima of the external periodic potential. As an application, we consider the diffusion of a dimer adsorbed on the crystal surface.