An electrostatic-variable coarse-grained model for predicting enthalpy of vaporization, surface tension, diffusivity, conductivity, and dielectric constant of aqueous ionic liquid

Electrostatics polarization effects are crucial in predicting various physical properties of pure or aqueous ionic liquids, which have potential applications as green solvents in many fields, such as chemical synthesis and gas separations. Here, we proposed an electrostatic-variable coarse-grained (VaCG) model to predict physical properties of water/[BMIM]+[BF4]- binary mixtures and pure [BMIM]+[SCN]- by introducing a concentration or environment-dependent dielectric constant of ionic liquid, εIL(x), and water, εw(x), in the non-bonded electrostatic interaction term, respectively. The electrostatic polarization induced charge transfer between cation and anion pair of ionic liquid was treated by setting the fragment charges of the three coarse-grained beads, i.e., butyl and methylimidazolium units of [BMIM]+ and anions ([BF4]-or [SCN]-), from the linear scaling generalized energy-based fragmentation electronic structure calculations of clusters with up to 30 cation–anion pairs. This model handles the polarization effect over the range of water mole fraction x = 0 ∼ 100 mol% with the explicit partial charges and implicit treatment of the long-ranged continuum medium without increasing the computational cost. The VaCG model has good performance in predicting thermodynamics (density, enthalpy of vaporization, surface tension), dynamic properties (diffusivity, ionic conductivity), and dielectric properties of aqueous solutions. This model is expected to be applicable to many other complicated systems with significant polarization effects.