The Direct Correlation-Function for A Fluid Of Hard Molecules

A new approximation is proposed for the direct correlation function of a homogeneous fluid of hard molecules. As in scaled particle theory [5], and in the scaled field particle theory of Rosenfeld [6] the direct correlation function is expressed as a linear combination of four basic functions representing different geometrical features of two molecules. In the new approximation the weights of the basic functions are determined in such a way that the approximate correlation functions satisfy four equations which are also satisfied by the Percus-Yevick (PY) solutions. When the method is applied to the hard sphere fluid with an appropriate choice of basic functions, it yields the PY solution for the correlation function.