Structure and stability of binary alloy surfaces: Segregation, relaxation, and ordering from first-principles calculations

Although modern computer codes based on density functional theory (DFT) allow the reliable prediction of many surface properties, they often cannot be applied, when the problem of interest demands a consideration of huge configuration spaces or model systems containing many thousand atoms. An important example are binary alloy surfaces where substitutional ordering phenomena on a mesoscopic scale and surface segregation are involved. It will be demonstrated how the combination of first-principle calculations with cluster expansions (CE) and Monte-Carlo (MC) simulations allows for a quantitative prediction of disordered alloy surface properties without any empirical parameters. The concept will be applied to the Pt25Rh75(111) surface. Our results are in excellent agreement with experimental studies.