Ab initio ground-state study with fourth-nearest-neighbor cluster interactions for fcc Pd-V alloys

A cluster expansion is used to predict the fcc ground states, i.e., the stable superstructures at zero kelvin as a function of composition, in a binary alloy system. The intermetallic fcc superstructures are not assumed, but derived rigorously by minimizing the configurational energy subject to linear constraints. This ground-state search includes pair and multiplet interactons which spatially extend to fourth-nearest neighbor. A large number of these concentration-independent interactions are computed for the Pd-V system by the method of direct configurational averaging using a linearized-muffin-tin-orbital Hamiltonian cast into tight-binding form. With these interactions, derived without the use of any adjustable or experimentally derived parameters, it is possible to make an exact ground-state search on the fcc lattice. Agreement with the fcc-based portion of the experimentally determined Pd-V phase diagram is excellent.