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 order-disorder 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.