VAPOR-LIQUID-EQUILIBRIA OF THE LENNARD-JONES FLUID FROM THE NPT PLUS TEST PARTICLE METHOD

Using an improved version of the recently suggested NpT + test particle method, phase equilibria are determined for the Lennard-Jones fluid in the temperature range T* = 0.70 to T* = 1.30 in steps of DELTA-T* = 0.05. For the final results, gas simulations are necessary only at the two highest temperatures; for T* = 1.20 and downwards the gas phase can be described with sufficient accuracy by the Haar-Shenker-Kohler equation. The resulting vapour pressures, bubble and dew densities can be correlated by the equations 1n p(sigma)* = 1.2629T* - 4.8095/T* - 0.15115/T*4, rho'* = rho(c)* + 0.477(T(c)* - T*)1/3 + 0.2124(T(c)* - T*) - 0.01151(T(c)* - T*)3/2, rho"* = rho(c)* - 0.477(T(c)* - T*)1/3 + 0.05333(T(c)* - T*) + 0.1261(T(c)* - T*)3/2, with the critical temperature and density being T(c)* = 1.310 and rho(c)* = 0.314, respectively. Then a detailed comparison with other simulation results and perturbation theory results is given. Outstanding findings are that the present data are rather smooth, that they match quite well the early data of Hansen and Verlet (1969, Phys. Rev., 184, 151) and are much closer to perturbation theory than most previous results. Finally, using the vapour pressure equation and directly calculated volume changes and enthalpies of vaporization in combination with the Clausius-Clapeyron equation reveals excellent thermodynamic consistency in the present results.