Extension of the TraPPE-UA force field to the simulation of vapor-liquid phase equilibria of vinyl acetate system

An extensional TraPPE-UA force field, based on a Lennard-Jones plus point charge functional form, for vinyl acetate is proposed. The Lennard-Jones well depth and size parameters for the group CHoc(sp2) was fitted by calculating configuration interaction energy of vinyl acetate with quantum chemistry method, while the remaining Lennard-Jones parameters were taken from the transferable potentials for phase equilibria-united atom force field (TraPPE-UA). Point charges are determined from an electrostatic potential (ESP) analysis of ab initio calculations performed at the MP2/6-311G (d, p) level. Gibbs ensemble Monte Carlo simulation in the NVT ensemble was presented to determine the vapor-liquid coexistence curves, vapor pressures, and critical points of vinyl acetate predicted by the new force field. Accurate description of the phase equilibria of vinyl acetate was obtained with the extensional TraPPE-UA force field, with mean unsigned errors in the saturated liquid density of less than 10%. Better results for critical temperature and density were obtained, while the saturated vapor pressures predicted by the new force field were relatively underestimated.