Computation of configurational entropy using Monte Carlo probabilities in cluster-variation method entropy expressions

We study the applicability of a combined approach to the calculation of free energies in lattice models using Monte Carlo simulations and several cluster-variation method (CVM) entropy expressions. We demonstrate that very accurate free energies can be obtained for ordered and disordered phases at arbitrary chemical field and temperature without thermodynamic integration, provided that use is made of high-order CVM entropy expressions. We also present a novel approach to grouping clusters into symmetry equivalent groups during a Monte Carlo simulation without prior knowledge of the space-group of the phase being sampled.