Ising-like Description of Structurally Relaxed Ordered and Disordered Alloys

We demonstrate the ability of generalized Ising-like cluster expansions to describe the energetics and thermodynamics associated with large atomic displacements in alloys. Although the expansion is constructed only from the energies of a few (small-unit-cell) ordered structures, it provides accurate predictions of the atomically relaxed energies of random, ordered, or partially ordered alloys, as compared with direct, large scale energy-minimizing simulations. Relaxed energies are obtained without having to compute relaxed geometries. Combination of the expansion with Monte Carlo simulations is shown to provide an efficient means for calculating thermodynamic properties.