Chemomechanics in alloy phase stability

This work introduces a first-principles statistical mechanics method to calculate the free energies of crystalline alloys, including dependence on temperature, composition, and strain. The approach extends the alloy cluster expansion to include an explicit dependence on homogeneous strain in addition to site occupation variables that track chemical ordering. The method is applied to the Si-Ge binary alloy and is used to analyze phase stability under arbitrary epitaxial constraints. As a surrogate model, the new cluster expansion is a convenient compromise between the more restrictive configuration-only cluster expansions and machine-learned interatomic potentials, which require a substantially larger effort to train.