Vapour-liquid coexistence curves of the united-atom and anisotropic united-atom force fields for alkane mixtures

The performances of two categories of force field for mixtures of alkanes are compared. Configurational-bias Monte Carlo simulations in the Gibbs ensemble were carried out to compute the vapour-liquid coexistence curves (VLCC) for pure n-pentane and n-dodecane and for binary mixtures of these components with methane. The united-atom (UA) force field (Siepmann and coworkers) and the anisotropic united-atom (AUA) force field (Toxvaerd) were used in this study. It is shown that the use of the recently readjusted versions of these potential forms together with the Lorentz-Berthelot mixing rules yields a description of the VLCC of methane-n alkane binary mixtures that is as accurate as the description of the pure component obtained with the same UA/AUA force field.