Thermodynamics and structure of liquid alkali metals from the charged-hard-sphere reference fluid

The evaluation of thermodynamic properties of liquid alkali metals is reexamined in the approach based on the Gibbs-Bogoliubov inequality and using the fluid of charged hard spheres in the mean-spherical approximation as reference system, with a view to achieving consistency with the liquid structure factor. The perturbative variational calculation of the Helmholtz free energy is based on an ab initio and highly reliable nonlocal pseudopotential. Only limited improvement is found in the calculated thermodynamic functions, even when full advantage is taken of the two variational parameters inherent in this approach. The role of thermodynamic self-consistency between the equations of state of the reference fluid derived from the routes of the internal energy and of the virial theorem is then discussed, using previous results by Ho?ye and Stell [J. Chem. Phys. 67, 439 (1977)]. An approximate evaluation of the corresponding contribution to the free energy of liquid alkali metals yields appreciable improvement in both the thermodynamic functions and the liquid structure factor. It thus appears that an accurate treatment of thermodynamic self-consistency in the charged-hard-sphere system may help to resolve some of the difficulties that are commonly met in the evaluation of thermodynamic and structural properties of liquid metals.