Radial Density Functions for Liquid Mercury and Lead

The effects of data termination and systematic errors on the radial distribution functions of liquids obtained from x-ray diffraction data are investigated with the aid of a computer. A general procedure for the elimination of spurious detail is presented, and new data for liquid mercury and lead are analyzed. Comparisons of radial distributions for the solid and the corresponding liquid near the melting temperature show that the radial density functions for the liquid and the corresponding crystalline solid are strikingly similar, whereas liquid lead is different from liquid mercury. The liquid structure may be described by starting with the structure of the polycrystalline solid and specifying the following parameters: The mean nearest-neighbor distance $r_1$; the average density of the liquid ${\rho }_0$; the critical correlation distance $d$; and the mean-square relative displacements between atom pairs, ${\sigma }^2$. The ${\sigma }^2$ vary with pair separation and include both thermal vibrations and diffusive motions. The mean nearest-neighbor distance in the liquid is shown to be smaller than in the solid.