The dielectric constant and the site-site direct correlation function of the RISM-2 theory for polar polyatomic molecular fluids

Abstract

The exact expression of the dielectric constant for polar polyatomic molecular fluids is obtained in terms of the site-site direct correlation function. This equation is closely related to the formula of the dielectric constant in terms of the molecular direct correlation function (the Ramshaw equation, Ramshaw, 1972, J. chem. Phys., 57, 2684). We discuss why RISM-1 theory gives a trivial expression for the dielectric constant using equations obtained here, and show that RISM-2 theory leads to a non-trivial result for the dielectric constant of molecular liquids.