Application of the functional renormalization group method to classical free energy models

A simple functional renormalization group method is presented to correct the behavior of classical free energy models near the critical point. This approach is applied to the Soave-Redlich-Kwong equation of state to illustrate its ability to better reproduce the phase behavior of simple fluids and to understand the influence of its parameters on the shape of the vapor-liquid phase diagram. The method is then extended to account for the correlations induced by intramolecular bonds. It is then applied to a first order thermodynamic perturbation theory for chain fluids to examine fluids composed of linearly bonded Lennard-Jones atoms. Unlike previous approaches for applying renormalization group corrections to chain fluids, this is able to accurately reproduce the critical point without predicting an overly flat liquid-vapor coexistence region.