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