Density Dependent Potentials in Simple Liquids

The density dependence of effective pair potentials may be studied through the density dependence of the liquid structure factor. For a liquid alkali metal (Rb) it is suggested that the ρ1/3 behavior of the Fermi wave-number of the electron gas explains the ρ1/3 behavior of the liquid structure factor recently discovered by Egelstaff et al. For the Lennard-Jones fluid and for liquid neon it is suggested that a near ρ-independent potential gives rise to ρ-dependent changes in the liquid structure factor corresponding to changes in the number of nearest neighbors in real space. This suggestion is tested by comparison with experiment.