First-Principles United Atom Force Field for the Ionic Liquid BMIM + BF 4 – : An Alternative to Charge Scaling

Molecular dynamics study of ionic liquids (ILs) is a challenging task. While accurate fully polarizable atomistic models exist, they are computationally too demanding for routine use. Most nonpolarizable atomistic models predict diffusion constants that are much lower than experiment. Scaled charge atomistic models are cost-effective and give good results for single component ILs but are in qualitative error for the phase behavior of mixtures, due to inaccurate prediction of the IL cohesive energy. In this work, we present an alternative approach for developing computationally efficient models that importantly preserves both the correct dynamics and cohesive energy of the IL. Employing a "top-down" approach, a hierarchy of coarse-grained models for BMIM(+)BF4(-) are developed by systematically varying the polarization/atomic resolution of the distinct functional groups. Parametrization i…