Surface molecular dynamics simulation with two orthogonal surface steps: how to beat the particle conservation problem

Due to particle conservation, canonical molecular dynamics (MD) simulations fail in the description of surface phase transitions involving coverage or lateral density changes. However, a step on the surface can act effectivel y as a source or a sink of atoms. in the simulation as well as in real life . A single surface step can be introduced by suitably modifying planar peri odic boundary conditions. to accommodate the generally inequivalent stackin g of two adjacent layers. We discuss here how. through the introduction of two orthogonal surface steps, particle number conservation may no longer re present a fatal constraint for the study of these surface transitions. As a n example, we apply the method for estimating temperature-induced lateral d ensity increase of the reconstructed Au(0 0 1) surface. the resulting aniso tropic cell change is consistent with experimental observations. Moreover. we implement this kind of scheme in conjunction with the variable curvature MD method. recently introduced by our group. (C) 2001 Elsevier Science B.V . All right reserved.