Surface tension and vapor–liquid phase coexistence of the square-well fluid

Vapor–liquid interfacial tension of square-well (SW) fluids is calculated using three different methods viz., molecular dynamics (MD) with collision-based virial evaluation, Monte Carlo with virial computed by volume perturbation, and Binder’s density-distribution method in conjunction with grand-canonical transition-matrix Monte Carlo (GC-TMMC). Three values of the SW attractive well range parameter were studied: λ=1.5, 1.75, and 2.0, respectively. The results from MD and GC-TMMC methods are in very good mutual agreement, while the volume-perturbation method yields data of unacceptable quality. The results are compared with predictions from the statistical associating fluid theory (SAFT), and SAFT is shown to give a good estimate for the systems studied. Liquid and vapor coexistence densities and saturation pressure are determined from analysis of GC-TMMC data and the results are found to agree very well with the established literature data.