Calculation of the dielectric constant of polyatomic fluids with the interaction site formalism

The proper integral equation theory for interaction site models of polyatomic fluids is used to study the static dielectric constant, ε. It is shown that the well known failure of the RISM theory to improve upon the ideal gas result, ε−1=3y, is a consequence of the RISM approximation in which the hypervertex functions, Ω, are replaced by their low density limit, ω. By accounting for the differences between Ω and ω, non-trivial results for ε are obtained, and these results do not require the use of unusual long ranged direct correlation functions. An illustrative calculation is presented to show that the ε −1 renorrnalization of bare coulombic interactions leads in the interaction formalism to the Onsager saturation ε∝y for large ε.