(185a) Viscosity and Phase Equilibria Prediction Via a Virial Optimized Site-Site M-6-8 Potential

Simulation methods for virtually any thermophysical property for any material have been developed and well-documented in the literature. However, the accuracy of chemical simulations is limited by the accuracy and transferability of the intermolecular force models used in the computations. The majority of current force fields are effective two-body potential models of the Lennard-Jones 12-6 form with parameters optimized for a subset of properties (density, heat of vaporization, phase equilibria, etc.) and usually for a subset of compounds (hydrocarbons, alcohols, proteins, etc.). When the parameters are used for other properties or compounds, the accuracy of the simulations decreases. Recent work shows that including an additional term in the dispersion series improves the predictive capabilities of molecular-scale simulation. United atom site parameters for the so called ?m-6-8? potential have been optimized to second virial coefficient data for ethane, n-butane, isobutane, and neopentane. The resulting force field was then used to predict second and third virial coefficients, gas phase viscosities, and phase equilibria of small to medium linear and branched alkanes. Further improvement in the predictability of phase equilibria and third virials was obtained by adding a three-body, Axilrod-Teller triple-dipole dispersion potential to the force calculation.