Structure and thermodynamics of polar interaction site fluids

We present results for the structure and thermodynamics of the dipolar hard dumbbell fluid obtained from a recently developed theory which is based on an extension of cluster perturbation theory (CPT) for atomic fluids to the interaction site formalism. The calculations are for the lowest order result in the theory which we denote as the optimized random phase approximation in the interaction site formalism (ISF-ORPA). This method does not include unallowed diagrammatic contributions to the structure and thermodynamics, in contrast to previous CPTs in the interaction site formalism. We compare the results to computer simulation data and find that the theory gives a realistic representation of the effect of the electrostatic interactions on the structure of the fluid.