A note on stochastic methods for trajectory simulations of atom-surface collisions

We analyze equations of motion which mimic successfully the process of ener gy transfer in multiple collisions of an atom or molecule with a surface. A Langevin model with a spatially dependent friction coefficient is consider ed. Similar to our previous model [D.V. Shalashilin, B. Jackson, J. Chem. P hys. 109 (1998) 2856] we assume that the friction is proportional to the re pulsive force between the incident particle and the surface. Unlike the sta ndard Langevin equation with constant friction coefficient, the energy diss ipation is localized near the region of closest encounter, which is more co nsistent with the physics of energy exchange. The approach is tested on a f lat surface model with a truncated harmonic particle-surface interaction, a nd on a realistic model describing the scattering of hydrogen atoms from a corrugated copper surface. Quantitative agreement with exact trajectory sim ulations (full slab calculations) has been achieved over a broad range of t emperatures. (C) 2000 Elsevier Science B.V. All rights reserved.