Applications of the cluster variation method to empirical phase diagram calculations

The treatment of short- and long-range order is an important problem in the modelling of solid solutions, and therefore in the modelling of order-disorder phase transitions. This can be correctly handled by the cluster variation method (CVM). The basis of this method are briefly recalled. The methods of resolution of the CVM are outlined with their advantages and disadvantages. The input parameters of the CVM are the cluster interactions which can be obtained either by ab-initio calculations of total energies (or energies of mixing) or by fitting thermodynamic experimental data. This last method, called the mixed CVM-CALPHAD, has been used in the past to calculate binary and ternary systems. Some examples are given, and the various strategies employed are described. A review of the systems, binaries and ternaries, for which the mixed CVM-CALPHAD has been used to compute the phase diagram is proposed.