Dual Critical Points and Related Phenomena in Simple Fluids from the Perspective of (Approximate) Renormalization Theory

It is known that some single component fluids can have coexisting low-density and high-density liquid phases with two, separate, gas–liquid and liquid– liquid, critical points. Such behavior is found both by experiments and in recent molecular-dynamics simulations performed for certain simple isotropic attractive pair potentials with softened repulsive cores. In the present investigation, a “global” renormalization group theory that was employed previously to make predictions for simple Lennard–Jones and square-well fluids over wide ranges of density and temperature, including the critical point, in reasonably good agreement with molecular dynamics and MoInte Carlo simulations, is applied to simple shoulder potentials and to square-well potentials with softened repulsive cores. Results using this renormalization approach are compared with some previously reported results for a shoulder potential and expectations regarding dual critical points for water.