Monte Carlo method for simulations of adsorbed atom diffusion on a surface

We present a simulation method for describing the diffusion processes of adsorbed atoms on a covalently bound surface. The method takes advantage of the benefit of the Monte Carlo technique for extending the time scale in simulations, and it is independent of the lattice type of the surface. It is particularly useful in the study of the diffusion processes on a surface with structural and/or chemical inhomogeneity. As a simple illustration of the method, we apply it to study hydrogen diffusion on a relaxed regular diamond {111} surface and an irregular diamond {111}-like surface. Four and five local minima for adsorption of a hydrogen atom are found on the regular diamond {111} surface and the irregular surface, respectively. The activation energies, the vibrational frequencies and the total escape rates of the hydrogen atom at each minimum are determined. The mean square displacement and diffusion constant of the hydrogen atom on the surfaces are also calculated. The results indicate that the Monte Carlo method is effective to investigate the diffusion processes of atoms on an arbitrary surface.