Ising model phase-diagram calculations in the fcc lattice with first- and second-neighbor interactions

Phase diagrams for a model fcc binary alloy with first- and second-neighbor interactions are calculated in the tetrahedron-octahedron approximation of the cluster-variation method. The calculations are carried out for two values of the ratio of second- to first-neighbor pair interactions in the range of 0 to 0.5, where the low-temperature-ordered structures occur at stoichiometries $A_2{B}_2$, $A_{2}B$, $A_{3}B$, and $A_{5}B$.