Surface Segregation in Transition Metal Alloys: From Electronic Structure to Phase Portraits

Abstract

The empirical models using pairwise interactions cannot be used to treat surface segregation in transition metal alloys, but we show that an effective Ising hamiltonian can be derived from their electronic structure. In addition to this Tight Binding Ising Model (TBIM) developed for a rigid lattice, a size-mismatch energy can be defined from quenched molecular dynamics calculations performed within the same tight-binding approximation. This energetic model can be coupled with a mean field approximation formulated in terms of phase portraits. Applications to some spectacular and recently observed surface phase transitions are presented.