Molecular dynamic simulations and global equation of state of square-well fluids with the well-widths from λ = 1.1 to 2.1

Abstract

We present the results of extensive new molecular dynamic (MD) simulations in the one-phase region for square well fluids with well widths λ = 1.10, 1.15, 1.20, 1.25, 1.375, 1.50, 1.75, 1.90, 2.0, and 2.10. These data have been used in developing a crossover equation of state (CR EOS) for square-well fluids with well widths 1.1 ≤ λ ≤ 2.1. The CR EOS incorporates non-analytic scaling laws in the critical region, and in the limit of low densities yields the exact second and third virial coefficients. Also in the high-temperature region, it reproduces first-order perturbation theory results. The CR EOS was tested against our new MD simulations, and earlier MD and Monte-Carlo (MC) simulations reported by other authors as well. Excellent agreement between calculated values and simulation data for all SW fluids is observed. In combination with the density-functional theory, the CR EOS is also capable of reproducing surface tension simulations with high accuracy. Application of the CR EOS for solid–liquid equilibrium calculations in combination with the Lennard–Jones and Devonshire cell model for the solid phase, is also discussed.

Keywords:

• Computer simulations
• Critical point
• Crossover theory
• Equation of state
• Square-well fluids
• Solid–liquid equilibria (SLE)
• Surface tension
• Thermodynamic properties
• Vapor–liquid equilibria (VLE)

Acknowledgements

The research in the Colorado School of Mines was supported by the US Department of Energy, Office of Basic Energy Sciences, under Grant No. DE-FG03-95ER14568. JRE acknowledges support from the NIST-CSTL group, Boulder, CO for two summer visits, and from ChemStations, Inc. Houston, TX, for support of the SPEADMD project.