Direct correlation function: Hard sphere fluid

The direct correlation function c(r) and in particular the "tail" of the direct correlation function d(r) are calculated for hard spheres from reliable expressions for the radial distribution function of the hard sphere fluid. This permits a direct examination of the Percus-Yevick (PY) approximation d (r) = 0. It is found that the PY approximation is very poor over-all but fairly reasonable in the most important region r ≥ σ. Finally a simple but relable parametrization of d (r) for hard spheres is proposed. Copyright © 1975 American Institute of Physics.