NONEQUILIBRIUM MOLECULAR-DYNAMICS SIMULATIONS OF 3-METHYLHEXANE - THEEFFECT OF INTERMOLECULAR AND INTRAMOLECULAR POTENTIAL MODELS ON SIMULATED VISCOSITY

Nonequilibrium molecular dynamics simulations of viscosity were perfor med using various molecular representations of 3-methylhexane in order to study the influence of potential models on simulated viscosity. Th e models investigated were united atom models with fixed bond lengths and bond angles. The effect of intermolecular potential was examined b y comparing results from a homogeneous (in which all -CHx groups are e quivalent) model and two heterogeneous models. The effect of intramole cular potential was investigated by comparing results from three diffe rent torsional potential models. The simulations were carried out at t hree different densities to investigate the sensitivity of the contrib utions from the various models to the viscosity at different condition s. Large changes in viscosity were produced by relatively small change s in the intermolecular potential parameters of the branched methyl gr oup. The viscosity was found to be less sensitive to the intermolecula r potential parameters of the chain methyl groups and the torsional po tential. Our results suggest that an accurate representation of the mo lecular structure and size as governed by intermolecular interactions is more important in accurate viscosity predictions than careful model ing of the intramolecular potential.