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. 1.