A molecular dynamics simulation of the diffusion of sodium adatoms on a Cu(001) surface was performed. A pair-wise Morse potential, fitted to the adatom adsorption geometry, binding energy, vibrational frequencies and activation energy for diffusion was used to model the sodium-copper interaction. Good agreement was obtained with quasi-elastic helium scattering data for the system, confirming the interpretation that sodium diffused by jumps from one four-fold hollow site to another with an effective activation energy of 51meV and a jump attempt frequency of 0.53THz. The measured jump rate was lower than that predicted by transition state theory. The molecular dynamics simulation suggested that this discrepancy arose because the rate of energy transfer between the adatom and the substrate was so slow that it controlled the attempt rate rather than the vibrational frequencies of the adatom as transition state theory would predict.

A Molecular Dynamics Simulation of the Diffusion of Sodium on a Cu(001) Surface. Ellis, J., Toennies, J.P.: Surface Science, 1994, 317[1-2], 99-108

Table 12

Energies and pre-exponential factors for migration on Cu(001)