Thermodynamic properties of liquid metals

The ability of the model potentials to yield accurate thermodynamic properties of liquid metals is tested. The pressure and bulk moduli calculated by the homogeneous deformation (HD) method depend on the electron density derivative of the self energy. The latter is determined predominantly by the choice and specification of the bare ion form factor for q>2ksub(F). Most of the empirical model potentials in the literature have been tested to give good description only in the region 0<=q<=2ksub(F). The bare ion form factor widely differ from one another for q>2ksub(F) and are not tested to give good description in this range. Therefore no meaningful calculation of the pressure and bulk moduli of liquid metals could be made at present by the HD method. The long wavelength (LW) method of calculating the bulk moduli involve only the pair potential, which is determined mainly by the choice and specification of the bare ion form factor in the region 0<=q<=2ksub(F). Therefore the LW method can give quantitative results for the compressibility. For Na and K, pair potentials calculated from Shaw's full non-local, energy dependent pseudo-potentials with the inclusion of appropriate effective masses and depletion hole charges is found to give remarkably good results for volume independent properties such as the packing fraction, entropy, constant volume specific heat, the long wavelength of the structure factor and the bulk modulus calculated by the LW method. The Ashcroft model potential is the best of all available local model potentials, but being a local one parameter potential can give only semi quantitative results for cohesive energy and bulk modulus calculated by the LW method. (author)