Some properties of the compound energy model

Abstract

The compound energy model is a modification of the bond energy model. It is based on the use of model parameters defined as Δ 0U AB = 0U AB − a′ 0U AA − a″ 0U BB, where a′ and a″ are stoichiometric coefficients in a compound A a′B a″ and may be different. The bond energy model was originally defined for a′ = a″ = 1 2 and uses a model parameter v AB = E AB − E AA 2 − E BB 2 . Recently, Oates and Wenzl also extended the bond energy model to the case a′ ≠ a″ but only under the condition that there are no bonds inside a sublattice. It is now shown that their treatment is identical to the compound energy model in the case of two sublattices. It appears as a semantic question whether or not the method of solving the problem appearing when a′ ≠ a″ justifies the new name “Compound Energy Model” or not. For higher order systems the treatment by Oates and Wenzl differs from the compound energy model in that it uses less parameters. The crucial question is whether this can be justified theoretically or should be regarded as an arbitrary choice of the relation between the parameters in the compound energy model. The compound energy model can be used for Monte Carlo simulations of short range order in systems with two sublattices when there are no bonds inside the sulattices or when all sites are equivalent as in AuCu 3.