Comparison between ab initio and polarizable molecular dynamics simulations of 1-butyl-3-methylimidazolium tetrafluoroborate and chloride in water

Abstract

In this study we compare the results of three different polarizable molecular dynamics force fields with an ab initio trajectory of the aqueous mixture of 1-butyl-3-methylimidazolium tetrafluoroborate and chloride, especially regarding their ability to describe static and dynamic phenomena. The discrepancies are discussed in terms of intra- and intermolecular force field parameters as well as the system size. We report significant differences in the derived diffusion coefficients and attribute them to system size, density and general discrepancies between ab initio and classical molecular dynamics simulations. In most cases, radial distribution functions show qualitative agreement; however, the overpolarization of chloride in the MD trajectories gives rises to unphysical results. Excellent agreement between dipolar distributions point out the importance of explicit polarizability in MD, while the comparison of computational and experimental IR spectra highlights the similarities between classical and ab initio dynamics in the low-wave number region and the differences around 1500 cm−1.