Abstract: TraPPE-UA and OPLS-AA force fields were used to investigate the applications of the Gibbs ensemble Monte Carlo (GEMC) method and the Gibbs-Duhemintegration (GDI) method in predicting the vapor-liquid equilibrium properties. It was found that the GDI method was much faster than the GEMC method if all-atom force field was employed. Based on the calculation results, the two methods could be viewed as complementary to the problem of vapor liquid coexistence. The calculated liquid densities, enthalpies of vaporization, critical temperatures, and critical densities by the two methods were very close to each other for a given force field. If the force field caused errors in the calculated heats of vaporization, the calculated vapor pressures and densities by the two methods were clearly different, which also led to difference in the predicted critical pressure.

Key words: Force field, Molecular simulation, Vapor-liquid equilibrium