H diffusion on Ni(100): A quantum Monte Carlo simulation

We have determined the diffusion constant for H on Ni(100) using the path-centroid formula for the transition rate, the embedded atom method for the potential, and the numerical quantum Monte Carlo technique. We find a distinct transition from semiclassical motion over the barrier to quantum tunneling through the barrier, in accordance with recent experiments by Lin and Gomer. The diffusion constant at high temperatures agrees with the experimental results; the transition, however, is located at too low a temperature (40 K) compared with experiment (100 K).