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

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Abstract
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.