Auxiliary sites in the RISM approximation for molecular fluids

One of the interesting features of the RISM approximation for molecular fluids is that the results of the theory show dependence on the presence or absence of auxiliary (i.e. non-interacting) sites. The authors examine this dependence analytically and numerically. Using graph-theoretical methods the diagrammatic expansions for the site-site correlation functions are examined in great detail in order to explain the way in which the dependence of auxiliary sites arises in the RISM approximation. This provides considerable insight into the nature of the RISM approximation itself.