First-principles calculations of the phase diagrams of noble metals: Cu-Au, Cu-Ag, and Ag-Au.

It is shown how the temperature-composition phase diagrams and thermodynamic properties of noble-metal alloys can be accurately reproduced by solving the three-dimensional nearest-neighbor fcc Ising model with volume-dependent interaction energies determined from the properties of the ordered phases alone. It is found that lattice relaxation effects are essential in determining orderdisorder critical temperatures. This approach enables the understanding of phase diagrams in terms of the electronic properties and atomic-scale structure of the constituent ordered phases.