Simulations of tracer diffusion in the pressure range of 0 to 200 atmospheres were carried out in order to explore the relationship between surface diffusion and the pressure in the gas phase. Calculations were performed for a model system describing the diffusion of an atom-like particle on the Ru(001) surface. A diffusion mechanism deduced from careful analysis of a large number of individual trajectories clarified the relationship between the pressure, and both the pre-exponential factor and the diffusion activation energy.

Tracer Surface Diffusion at High Pressures: Molecular-Dynamics Study. Zeiri, Y.: Journal of Chemical Physics, 2000, 113[9], 3868-73