Self-diffusion coefficient of two-center Lennard-Jones fluids: Molecular simulations and free volume theory

Abstract

A comprehensive investigation is conducted to study the thermodynamics, structure, and mean free volume of rigid two-center Lennard-Jones fluids through Monte Carlo simulations. For a large number of states, the self-diffusion coefficient is computed using the following two different approaches: the equilibrium molecular dynamics simulation method and the modified Cohen-Turnbull theory. The effects of the bond elongation on different thermophysical properties are studied. The generic van der Waals theory, which has recently been extended to rigid polyatomic fluids [A. Eskandari Nasrabad and R. Laghaei, J. Chem. Phys. 125, 154505 (2006)], is used to compute the mean free volume needed in the modified Cohen-Turnbull theory. The effective site diameter is computed using the virial minimization method and the results are applied within the generic van der Waals theory. The Gibbs ensemble Monte Carlo simulation technique is applied to determine the location of the fluid phase envelope. The NVT Monte Carlo simulation method is then utilized to compute the equation of state and the correlation functions appearing in the generic van der Waals theory. It appears that the logarithm of the mean free volume versus density is almost linear at rho>rho(c) independent of the bond length, which suggests a universal behavior. The self diffusion coefficient results of the modified Cohen-Turnbull theory are analyzed in detail.