Stimulated diffusion of an adsorbed dimer.

The mobility and the diffusivity of a dimer (two atoms coupled by an elastic spring) in a periodic substrate potential under the action of the dc and ac external forces are studied. It is shown that the dimer diffusivity may be strongly enhanced due to driving.

Long jumps in the strong-collision model.

The jump-length probability distribution for a classical particle diffusing in a periodic potential is calculated in the framework of a strong-collision model, where each collision of the particle with the thermal bath reequilibrates the velocity. Exact numerical results are obtained by the matrix-continued-fraction method, and two different analytical approximations are developed. In the first approximations it is assumed that an activated particle is always retrapped in the cell where it suffers the first collision; in the second approximation it is assumed that only the collisions giving a final total energy which is lower than the activation barrier are effective for retrapping.