## Overview

The origin of cluster expansions can be traced back to the early 1950s, when Kikuchi developed an Ising model-based cluster variation method to study order-disorder phenomena. In 1984, Sanchez et al. developed a general formalism for the description of configurational cluster expansions in terms of a complete basis set expansion. In simple terms, CE decomposes the energy of a configuration into one-body, two-body, and higher-order interaction terms (‘clusters’), and each term has a corresponding weight called effective cluster interaction (ECI) analogous to the interaction strength. The energy can be exactly reproduced only if all clusters are included in... read more