An analytic expression for the first shell of the radial distribution function

A simple analytical expression fi~r the Iirst shell of the radial distribution function I RDV) is proposed. This expression, which has only three adjustable parameters, satislics all the limiting cases of the hard-sphere RDV at high temperatures, the ideal gas RDF tit z.gro density, the dilute-gas RDF tit low densities, and the location of the peak in the first shell. The only requirement is the introduction of a potential ftmction into the model. This theory has been applied to the Lcnnard Jones, Kihara. and square-well pair iIntermolecular potential energy functions. The first-shall RDI: results arc in good agreement with the axailablc computer simulation data for the RDF of the Lennard Jones fluid and the experimental data for argon. By introducing the radius of truncation for the RDV, it is shown that inlʹormation on the first shell of the RI)I- is sull]cient to predict macroscopic properties of Iluids. Calculations of radii of lrl.lncation OJ" RDF for various prol-~crties indicate that Ihey tire always in the rallgC of the firs! shell of RI)I".