Short-time collective dynamics of an ionic liquid: A computer simulation study with non-polarizable and polarizable models, and ab initio molecular dynamics.

This article focuses on evaluating the effects of including polarization via Drude oscillators in classical molecular dynamics (MD) simulations of the ionic liquid 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide, [C2C1im][FSI]. Comparing non-polarizable and polarizable classical MD models against ab initio molecular dynamics (AIMD) simulations and experimental data from far-infrared (FIR) and inelastic x-ray scattering (IXS) spectroscopies, the study finds that while the polarizable model improves long-time transport properties such as diffusion, viscosity, and conductivity, it excessively overdamps short-time intermolecular dynamics in the THz frequency range. The non-polarizable model and AIMD simulations better reproduce the experimental FIR and IXS spectra related to picosecond dynamics, indicating that polarization inclusion leads to stronger local interactions but faster relaxation of oscillations. Thus, the polarizable force field enhances transport coefficient predictions but compromises the accuracy of short-time dynamic behavior compared to experimental and AIMD references.