Structure and thermodynamics of liquid metals and alloys

Ab initio calculations of the structure and the thermodynamic properties of simple liquid metals and alloys are presented. The basic ingredients of the theory are as follows: (a) An orthogonalized-plane-wave-based first-principles pseudopotential is used to describe the interatomic forces. The pseudopotential is optimized specifically for binary systems. The Xα method is used to construct the electron-ion potential. (b) A system of hard spheres is used as a reference system for describing the liquid structure. Effective hard-sphere diameters are determined by a variational method based on the Gibbs-Bogolyubov inequality. The method of this paper yields encouraging results for the structure factors, the excess volume, and the enthalpy and entropy of formation for alloys with a nearly random distribution of the components. Difficulties arise where nonrandomness has to be expected. The theory provides a basis for a microscopic understanding of the thermodynamics of alloys of simple metals in terms of their electronic structure.