Structure and thermodynamics of discrete potential fluids in the OZ-HMSA formalism

We study the structural and thermodynamic properties of three discrete potential fluids: the square well (SW), the square well-barrier (SWB), and the square well-barrier-well (SWBW) fluids by means of the Ornstein-Zernike (OZ) integral equation and the HMSA (hybrid mean spherical approximation) closure relation. The radial distribution functions, structure factors, and pressure of the systems are calculated as a function of the strength of the attractive and repulsive parts of the potential in an extended range of densities, mainly covering the range 0.1 <= rho* <= 0.9. We find that far away from the liquid-vapour coexistence region the HMSA theory is an accurate approach that compares well with Monte Carlo simulations. We also find that when the attractive parts of the potential dominate over the repulsive part the structure factor at low q values shows a considerable increase, which suggests the formation of large-scale domains that locally exhibit fluid-like structure.