Grand Canonical Monte Carlo Simulations Guided by an Analytic Equation of State-Transferable Anisotropic Mie Potentials for Ethers.

Abstract

In this study, we propose using an analytical equation of state for guiding molecular simulations in the grand canonical ensemble. Molecular simulations in the grand canonical ensemble deliver phase equilibrium properties with low statistical uncertainty. The entire phase envelope can be obtained when histograms of several simulations along the phase envelope are combined. In this study, we explore the use of an analytical equation of state for defining chemical potentials, temperatures, and intervals of molecule numbers for simulations in the grand canonical ensemble, such that the phase envelope is traced. We limit particle numbers to intervals and ensure even sampling of molecule numbers in each interval by applying a bias potential determined from transition-matrix sampling. The methodology is described for pure components and binary mixtures. We apply the simulation method to develop parameters of the transferable anisotropic Mie (TAMie) force field for ethers. We find that the partial charges optimized individually for diethyl ether and for dipropyl ether differ substantially from the partial charges optimized simultaneously to both substances. The concept of transferable partial charges is thus a significant assumption. For developing the (TAMie) force field, we constrained the partial charge to a range, where individually optimized partial charges were found.