Ornstein-Zernike equation for convex molecule fluids

Structure of fluids is suitably characterized by distribution functions fro m which the most important is the pair correlation function. Theoretical ap proaches to get the pair distribution function are based mainly on the solu tion of the Ornstein-Zernike (OZ) integral equation. In this paper, the OZ equation for molecular fluids is modified to yield the average correlation function for systems of convex molecules. In our approach we employed the p reviously proposed method to separate the shape effect of molecular cores f rom that due to the variable surface-surface distances among three pairs of convex cores. The effect of nonspherical shape of hard cores in the convol ution integral is expressed through the derivative with respect to three su rface-surface distances of the expression for the hard convex body third vi rial coefficient. For simple fluids (with the pointwise cores) the derived expression reduces to the standard OZ equation. The modified OZ equation is solved numerically for the Percus-Yevick-type closure and the average corr elation functions in the systems of hard spherocylinders with l/sigma =0.4, 0,6 and 1 were determined. The obtained dependencies of the average correl ation functions on the reduced distances calculated from the modified OZ eq uation agree well with the simulation data for the above systems at relativ ely high densities. (C) 2001 American Institute of Physics.