Modified form of the cluster-variation method

Abstract

We present a new derivation of the cluster-variation method which is based on the constant-coupling approximation. We apply the method to derive the free energy for a face-centered-cubic binary alloy model with many-body interaction potentials. By modifying one of the assumptions made in deriving this result, we are able to generate a new approximation to the free energy of the alloy. Numerical comparisons of the original cluster-variation method and the new approximation are given for an fcc alloy with many-body interaction potentials. Some changes are observed in the phase diagrams, although the overall structure remains the same.