Generic force fields for ionic liquids

Ionic liquids have been intensively studied during the last decade, but many questions still remain unresolved. From the computational side there is the lack of good transferable force fields for molecular simulations that would allow accurate theoretical predictions and interpretations of the properties of ionic liquids. Within this article a method is described that allows for the derivation of partial charges for ionic liquids since they play a particular important role, particularly for a liquid that consists entirely of ions. Our partial charges are carefully determined in such a way that they incorporate in an average way the influence of polarization effects of the neighboring ions in a bulk situation thereby reducing the total ionic charge to values less than one. When combined with our recently introduced method for the optimization of the short-range interactions [1] we have a well described route to develop generic force fields for ionic liquids. In this article we describe our results for the partial charges for the three imidazolium based liquids [MMIM]+, [EMIM]+, and [BMIM]+ for three different anions.