THE CALCULATION OF LIQUID-VAPOR-EQUILIBRIUM FOR GROUP IA AND GROUP IIA METALS

Liquid-vapor coexistence curves for selected group IA and IIA metals a re calculated. The Gibbs-Bogoljubov variational method is used to find a least upper bound to the Helmholtz energy of the liquid phase. The hard sphere liquid is chosen to represent the structure of the metal m elt, and the empty-core pseudopotential is chosen to the model the pot ential energy of interaction in the liquid phase. The vapor phase is m odeled as an ideal gas mixture of monomers and dimers, with the distri bution of mole fractions determined by the canonical ensemble partitio n function. Parameters are chosen that model coexistence properties be tween the melting temperature and the boiling temperature of the liqui d metals. Good results are obtained for representative group IA and gr oup IIA metals.