Thermodynamic scaling Monte Carlo study of the liquid–gas transition in the square–well fluid

A Temperature–and–Density–Scaling Monte Carlo (TDSMC) study of the square-well fluid was carried out. The relative excess free energy was obtained directly from the simulations with a standard deviation less then 0.5%. Energy, pressure, compressibility and heat capacity were calculated from the excess free energy data. For the system of 256 particles a reduced density interval of 0.1-0.68 and a reduced temperature interval of 1.053-1.29 was covered. In the simulations a “zoom focus” on the temperature–density grid was used: a “panoramic view” of the whole temperature–density region, on a relatively coarse grid, was combined with a “close-up” of the critical–point region, using a finer (T,ρ) grid. The coexistence curve was obtained with use of the double–tangent construction on the free energy, and the critical temperature and critical density were estimated. The critical parameters found by the TDSMC method are compared with those of other Monte-Carlo techniques.