Effective Ising Hamiltonian for Surfaces of Metallic Alloys

Abstract

Ab-initio studies of bulk and surface phase diagrams and surface segregation are based on the Ising-type Hamiltonian, whose parameters are given by the effective cluster interactions (ECI). In bulk alloys the ECIs are determined either by the Connolly-Williams inversion scheme1 which extracts the ECIs from total energies of suitably chosen periodic structures, or by the generalized perturbation method (GPM)2, based on the expansion of the band energy term of the total energy of the completely disordered state described within the coherent potential approximation (CPA). The Connolly-Williams method yields concentration independent ECIs, while those determined by the GPM depend on the alloy concentration. Both approaches were recently generalized to the case of alloy surfaces3–7.