Overview no. 43. Binary ordering prototype phase diagrams in the cluster variation approximation

The Tetrahedron Octahedron Cluster Variation Method (TO-CVM) has been employed to investigate f.c.c. based order-disorder phase diagrams with first (positive) and second nearest neighbor pair interactions. The investigation covers the entire range of α values, the ratio of second to first nearest neghbor pair interactions. Ground state structures are discussed in detail and phase diagrams for seven different α values are presented. Good qualitative (topological features) and reasonable quantitative (transition temperatures) agreement is obtained with available Monte Carlo results, thereby confirm the reliability of the TO-CVM phase diagram calculations. The present study concludes the first global phase diagram investigation of f.c.c.-based Ising model with first and second nearest neighbor pair interactions, and can be regarded as a precursor to more elaborate first principles phase diagram calculations.