The diffusion coefficients of H2 on a clean Cu(111) surface at 50 to 150K were calculated by molecular dynamics simulation. The H2 molecule in the present study was treated not only as a rigid-rotor, but also having vibrational motion. In the simulations the phonon-molecule coupling was also considered. The ensemble-averaged square displacement as well as the velocity autocorrelation function were used for a range of energies to get the diffusion coefficients. The results obtained from the simulation were compared with the results from the calculations by a simple transition state theory. It was shown that the results from transition state theory underestimated the diffusion constant as compared with those obtained by molecular dynamics simulations.

Molecular Dynamics Study of H2 Diffusion on a Cu(111) Surface. Wang, L., Ge, Q., Billing, G.D.: Surface Science, 1994, 301[1-3], 353-63