Pair potential trends from the evidence of observed liquid-metal structure factors

The direct correlation functions c(r) of the simple liquid metals at their melting temperatures T_m are deduced from the measured structure factors, and the corresponding inter-atomic pair potentials inferred from v(r)=-k_BT_mc(r). In groups 1 and 2(a), each v(r) shows a pronounced negative minimum close to the preferred near-neighbour distance d (defined by the peak in the radial distribution function). In the remaining groups, the general picture is of v(r) positive at d with a weaker positive minimum beyond. The above features (and some other detail) are shared by potentials calculated using ab initio electron theory (empty-core pseudopotentials, Ichimaru-Utsumi screening), as detailed calculation and comparison show. A modified analysis is also presented in which some allowance is made for the role of the volume dependence of the forces. The qualitative features noted above are largely unchanged but there is no obvious general improvement in the quantitative comparison with the ab initio results.