Refining classical force fields for ionic liquids: theory and application to [MMIM][Cl

Abstract

Most of the force fields for ionic liquids cannot properly describe statics and dynamics. In this context, we propose an efficient method to adapt force fields, the basis of any classical molecular dynamics simulation. In the parameterisation process, a target function is minimized by a conjugate gradient based approach that vastly accelerates the tuning of the force field parameters through parallelization. As the description of the dynamics is captured in the parameterisation of the partial charges, we fit the short range parameters using only static properties, thus avoiding long simulations for the force field refinement. In the validation of the final parameterisation, the force field gives a good description of the dynamics in terms of the conductivity, especially in the temperature regime where the reference properties are matched very accurately. This method is sufficiently general and easily altered to fit an arbitrary set of reference properties, such that it can be considered for the construction of a versatile, transferable force field for ionic liquids.