Integral equations for molecular fluids based on the interaction site model: Density-functional formulation

An integral equation for rigid-body molecules with respect to site-density distribution function under arbitrary external fields is derived by the den sity-functional theory. Using a grand canonical partition function of molec ular systems, we extend original Percus' idea to molecular fluids. The exte nded Percus' idea provides a relation between the site-site pair distributi on function and site-density distribution function under an external field composed of the site-site interaction potentials of a molecule fixed at the origin. The site-density integral equation combined with the extended Perc us' relation to molecular fluids gives a closure relation of reference inte raction site model equation. The site-site pair distribution functions of h omonuclear diatomic Lennard-Jones fluids obtained by the integral equation agree well with those of Monte Carlo simulation. (C) 2001 American Institut e of Physics.