Transferable Potentials for Phase Equilibria. 1. United-Atom Description of <i>n</i>-Alkanes

Abstract

A new set of united-atom Lennard-Jones interaction parameters for n-alkanes is proposed from fitting to critical temperatures and saturated liquid densities. Configurational-bias Monte Carlo simulations in the Gibbs ensemble were carried out to determine the vapor−liquid coexistence curves for methane to dodecane using three united-atom force fields:  OPLS [Jorgensen, et al. J. Am. Chem. Soc. 1984, 106, 813], SKS [Siepmann, et al. Nature 1993, 365, 330], and TraPPE. Standard specific densities and the high-pressure equation-of-state for the transferable potentials for phase equilibria (TraPPE) model were studied by simulations in the isobaric−isothermal and canonical ensembles, respectively. It is found that one set of methyl and methylene parameters is sufficient to accurately describe the fluid phases of all n-alkanes with two or more carbon atoms. Whereas other n-alkane force fields employ methyl groups that are either equal or larger in size than the methylene groups, it is demonstrated here that usin...