BILFF: All-Atom Force Field for Modeling Triazolium- and Benzoate-Based Ionic Liquids

We present an extension of our previously developed all-atom force field BILFF (Bio-polymers in Ionic Liquids Force Field) to three different ionic liquids: 1-ethyl-3-methyl-1,2,3-triazolium acetate ([EMTr][OAc]), 1-ethyl-3-methyl-1,2,3-triazolium benzoate ([EMTr][OBz]), and 1-ethyl-3-methylimidazolium benzoate ([EMIm][OBz]). These ionic liquids are of practical importance as they have the ability to dissolve significant amounts of cellulose even at room temperature. Our force field is optimized to accurately reproduce the strong hydrogen bonding in the system with nearly quantum chemical accuracy. A very good agreement between the microstructure of the quantum chemical simulations over a wide temperature range and experimental density data with the results of BILFF were observed. Non-trivial effects, such as the solvation shell structure and π – π stacking of the cations, are also accurately reproduced. Our force field enables accurate simulations of larger systems, such as solvated cellulose in different (aqueous) ionic liquids, and is the first to present the optimized parameters for mixtures of these solvents and water.