Entropy derivation for cluster methods in non-Bravais lattices

The derivation of entropy for cluster methods is reformulated by constructing the probability of a given particle (spin) configuration as a self-consistent product of cluster configuration probabilities. This approach gives an insight into the nature of underlying approximations involved at different levels of the cluster-variation method. The graphical representation of the product allows us to extend this method for non-Bravais lattices as it is demonstrated on interstitial sites of body-centered- and face-centered-cubic crystals.