Polarizable Transferable Anisotropic United-Atom Force Field Based on the Mie Potential for Phase Equilibria: Ethers, n-Alkanes, and Nitrogen.

Abstract

This study proposes a Polarizable Transferable Anisotropic Mie (P-TAMie) force field for ethers and mixtures of ethers with n-alkanes and nitrogen. In our approach, polarizability is accounted for using a charge-on-spring model (also referred to as the Drude model or core-shell model) placed on every united-atom site. Parameters for polarizabilities are obtained from ab initio calculations, without the need to introduce empirical scaling factors. The van der Waals parameters and static partial charges are optimized to minimize deviations to experimental vapor pressure and coexisting liquid density data. Vapor-liquid phase equilibria are calculated using Monte Carlo simulations in the grand canonical ensemble, using a MC scheme with multiparticle moves. Correlation results for pure substances and predictions of mixture behavior obtained from the proposed polarizable force field (P-TAMie) are in good agreement with experimental data. We compare the polarizable force field with an analogous nonpolarizable force field, namely, the Transferable Anisotropic Mie (TAMie) force field, where both force fields share the same intramolecular force field and were parametrized using the same objective function. The comparison should thus single out the role of polarizability in predicting phase equilibria. The comparison of P-TAMie with the nonpolarizable TAMie force field, however, shows very similar results of both models. This study does not include water and aqueous mixtures or other pronounced polar substances.