A study was made of the rate of activated motion over multiple barriers. In particular, the correlated double jump of an adatom diffusing on a missing-row reconstructed (110) surface was considered. A transition-path theory was developed which showed that the activation energy was given by the minimum-energy trajectory which occurred in the double jump. This trajectory was calculated explicitly by using an effective-medium molecular dynamics simulation. A cusp in the acceptance region led to a vT pre-factor for the activated rate of double jumps. The theoretical and numerical results agreed.

Rate Theory for Correlated Processes: Double Jumps in Adatom Diffusion J.Jacobsen, K.W.Jacobsen, J.P.Sethna: Physical Review Letters, 1997, 79[15], 2843-6