Simple CVM-based approximations for the configurational entropy

TL;DR

This paper derives simple polynomial formulas for the variational configurational entropy using the cluster variation method, demonstrating rapid convergence of transition temperature and short-range order parameters in a face-centered cubic Ising model.

Contribution

It introduces polynomial approximations for CVM-based entropy and shows their effectiveness in modeling phase transition properties.

Findings

Polynomial expressions accurately approximate CVM entropy.

Transition temperature estimates converge quickly with approximation order.

Short-range order parameters match CVM results rapidly.

Abstract

It is shown how to derive simple polynomial expressions for the variational configurational entropy starting from the cluster variation method (CVM). As an example, first six terms of the expansion of the entropy in powers of the nearest-neighbour (NN) short-range order (SRO) parameter are obtained for the NN Ising ferromagnet on the face-centered cubic lattice using the tetrahedron (T-CVM) approximation. Calculated values of the transition temperature and the NN SRO parameter at the transition converge rapidly to their T-CVM counterparts as order of the approximation increases.