A ground-state search of a generalized, many-body Ising Hamiltonian whose interaction energies are determined from first-principles local-density calculations reveals that PtX intermetallics for X=Ni, Cu, Rh, and Pd will form stable ordered structures at low temperatures. In contrast, d-band tight-binding models universally predict phase separation in all late-transition-metal alloys. It is shown that the previously neglected s-electron cohesion is responsible for this phase stability.

• Received 28 December 1990

DOI:https://doi.org/10.1103/PhysRevLett.66.1753