Renormalization Group Theory for Fluids to Greater Density Distances from the Critical Point

A recently developed renormalization group (RG) theory for fluids begins with an expression for the free energy for repulsive interactions only, then employs an RG procedure to take into account contributions to the free energy that come from fluctuations of all wavelengths in the presence of attractive inter-molecular interactions of limited range. The theory has had some success in describing volumetric properties of real fluids at the critical point and out to distances within approximately ±50% of the critical point density. In the calculations, the density dependence of the radial distribution function for the repulsive interactions was ignored. The theory has now been modified to take that density dependence into account. Predictions of the theory as thus amended are compared with volumetric measurements made in argon near the critical point temperature for densities from zero to more than twice the critical point density.