Calculating the energy parameters for the CV and OPF methods

A method is proposed for calculating the energies ε   m (s)(with ε   m (s)being the energy of the m ‐configuration of a type s figure), which are parameters of the cluster variation (CV) method and the order parameter functional (OPF) method. An analytic expression is derived which describes the energy ε   m (s)in terms of power series expansion coefficients of the formation enthalpy of a disordered crystal. It is shown that a necessary condition for ordering is the presence of a nonlinear composition dependence of the formation enthalpy of a disordered crystal.