Variational thermodynamic calculation for simple liquid metals and alkali alloys

The authors first propose an approach for treating a correction from the higher-order perturbative terms to the usual low-order pseudopotential perturbation calculation for the one-valence-electron states in a disordered metal. Then, the previously used energy-independent non-local model pseudopotential (EINMP) with this correction is applied along with the original EINMP to the variational thermodynamic calculation in the framework of a hard-sphere reference system for the alkalis in the liquid phase and for the K-Rb, Na-K and Na-Cs liquid alloys. The results obtained for (i) the hard-sphere diameter, sigma , (ii) the isothermal compressibility, chi _T, and (iii) the excess entropy, S^exc, are carefully examined and discussed. It appears that in going from the pure alkalis to their binary alloys, (i) the change in sigma follows closely the concept of valence-electron charge transfer, introduced previously to interpret the corresponding concentration dependence of the electrical resistivities and (ii) the deviations of chi _T and S^exc from ideality for the Na-K and Na-Cs alloys are largely due to the valence-electron charge transfer, which affects sigma in S^exc and also affects the contribution from the volume dependence of the screening to chi _T.