Structure and thermodynamics of square-well and square-shoulder fluids

We have reinvestigated the structural and thermodynamic properties of the squarewell and the square-shoulder system using two different theoretical frameworks, i.e., the optimized random-phase approximation and the Rogers–Young integral equation. We discuss the limits of applicability of the respective concepts and compare the results with ‘exact’ Monte Carlo simulation results and with data obtained from a semi-analytic method proposed by Nezbeda for narrow wells. Using these correlation functions, we study in the framework of the modified-weighteddensity approximation the isostructural solid–solid transition predicted for narrow wells and narrow shoulders.