Quantum Monte Carlo simulation of atomic motion

The path-integral formulation of quantum mechanics is a suitable starting point for quantum simulation studies. We have considered H diffusion on the Ni (100)-surface at room temperature and below using the quantum Monte Carlo technique. The transition rate is determined using the path-centroid formulation and the simulations are based on a potential derived from recent first-principles calculations of the total energy. We find a marked change of the temperature dependence for the diffusion constant around 60 K, indicating that quantum tunneling between the ground states starts to dominate the diffusion process. The simulation results are compared with recent experimental findings. (C) 1999 Published by Elsevier Science B.V. All rights reserved.