An improved approach for predicting the critical constants of large molecules with Gibbs Ensemble Monte Carlo simulation

In this work we focus on predicting the critical temperature (Tc), critical density (ρc), and critical pressure (Pc) from Gibbs Ensemble Monte Carlo (GEMC) simulations. Our primary objective is to reduce the uncertainty associated with the critical point constants, particularly Pc, for large molecules. To achieve this goal, we demonstrate the advantages of using the Rackett equation to predict Pc compared to the traditional approach of using the Antoine equation. The main difference is that the Rackett equation utilizes liquid density (ρL) while the Antoine equation uses vapor pressure (Pv). The Rackett equation yields a better prediction of Pc than the Antoine equation because ρL values are more reliable than Pv values when obtained from GEMC simulations for the standard force field models. As either method will yield large uncertainties in Pc if the uncertainties in ρc and/or Tc are large, we also develop a statistically-rigorous experimental design to minimize the uncertainty in Tc, ρc, and Pc. The greatest improvement in uncertainty is found for ρc and Pc when compared to other contemporary methods.