The Influence of Bond Angle on Thermophysical Properties of Three-Center Lennard-Jones Fluids: Computer Simulation and Theory

Abstract

Abstract We carry out extensive computer simulations to study the phase equilibrium, thermodynamics, and diffusion coefficient of three-center Lennard-Jones (3CLJ) fluids with an emphasis on the effects of bond angle on these properties. We take into account several bond angles ranging from θ 0 = 60 to 180 degrees and two equilibrium bond elongations le = 1.0 and 0.5 (in Lennard-Jones length unit). Moreover, we study the fully flexible (FF) 3CLJ fluids for molecules with bond length 1.0. Gibbs ensemble Monte Carlo (MC) simulations are performed to compute the densities of the vapor-liquid coexisting phases and the vapor pressure, and direct three-phase (vapor-liquid-vapor) molecular dynamics (MD) simulations are carried out to calculate the surface tension. We then apply constant NVT MC simulations to obtain the internal energy, the pressure, and the pair correlation function, and utilize equilibrium MD simulations to compute the diffusion coefficient of systems with le = 1.0. In addition to MD simulations, the modified Cohen-Turnbull (mCT) theory is used to to compute the diffusion coefficient and the mean free volume appearing in the mCT relation is provided by the results of the Generic van der Waals (GvdW) theory. We show that the mCT theory is capable of reproducing the MD simulation values quite well over a wide range of density with slight overestimations at medium range. The angle dependence of different thermophysical properties are analyzed and discussed in details.