First principles calculation of phase diagrams for binary and ternary alloys

Phase diagrams of Rh-Cu-Ni, Ag-Cu-Au ternary systems and Cu-Rh, Ag-Cu binary systems are estimated by the Cluster Variation Method(CVM) combined with Density Functional Theory within Local Density Approximation(LMTO-ASA) The ground-state properties of several ordered structures are derived from LMTO-ASA calculations. The interaction parameters are obtained by Connolly-Williams method. The vibrational energy is estimated within Debye-Gruneissen approximation. For the ternary phase diagrams, the volume relaxation is described by adopting the microscopic version of Vegard's law. The resulting ternary phase diagrams show topologically good agreement with the experimental observations and are self-consistent with the binary phase diagrams. For the estimation of the binary phase diagrams, various methods are used for the estimation of configurational free energy. Octahedron-Tetrahedron cluster approximation is used such that the effect of 2nd nearest neighbor bonds are examined. For proper description of the volume relaxation, a new model is proposed from the aspects of cluster expansion. The effects of 2nd nearest neighbor interactions were significant in both systems of Cu-Rh and Ag-Cu.