Equilibrium properties of dense simple fluids in the presence of three-body forces

Abstract

Computationally convenient theoretical methods for calculating the structural and thermodynamic properties of a classical fluid in the presence of three-body forces are presented. The concept of the effective pair potential has been used to develop two approximations, one known as the Exp approximation for the pair correlation function and the other known as ORPA+B2 for the Helmholtz free energy. The theory has been applied to calculate the effect of the triplet potential on the radial distribution function for the hard-sphere and the Lennard-Jones fluids. At densities and temperatures away from the triple point the effect of the dipole–dipole–dipole and dipole–dipole–quadrupole interactions on the structure of fluids have been found to be small. It is shown that the direct correlation function outside the hard core is significantly affected by the presence of the three-body forces.