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

We analyze equations of motion which mimic successfully the process of energy transfer in multiple collisions of an atom or molecule with a surface. A Langevin model with a spatially dependent friction coefficient is considered. Similar to our previous model [D.V. Shalashilin, B. Jackson, J. Chem. Phys. 109 (1998) 2856] we assume that the friction is proportional to the repulsive force between the incident particle and the surface. Unlike the standard Langevin equation with constant friction coefficient, the energy dissipation is localized near the region of closest encounter, which is more consistent with the physics of energy exchange. The approach is tested on a flat surface model with a truncated harmonic particle–surface interaction, and on a realistic model describing the scattering of hydrogen atoms from a corrugated copper surface. Quantitative agreement with exact trajectory simulations (full slab calculations) has been achieved over a broad range of temperatures.