Analytical representation of the density derivative of the Percus-Yevick hard-sphere radial distribution function

Explicit analytical expressions are presented for the density derivative, partial derivative g(HS) (R; rho)/partial derivative rho, of the Percus-Yevick approximation to the hard-sphere radial distribution function for R <= 6 sigma, where s is the hard-sphere diameter and rho = (N/V) sigma(3) is the reduced density, where N is the number of particles and V is the volume. A FORTRAN program is provided for the implementation of these for R <= 6 sigma, which includes code for the calculation of g(HS) (R; rho) itself over this range. We also present and incorporate within the program code convenient analytical expressions for the numerical extrapolation of both quantities past R = 6 sigma. Our expressions are numerically tested against exact results. [GRAPHICS] .