Polarizable Force Field Development and Molecular Dynamics Simulations of Ionic Liquids

Abstract

A many-body polarizable force field has been developed and validated for ionic liquids (ILs) containing 1-methyl-3-alkylimidazolium, 1-alkyl-2-methyl-3-alkylimidazolium, N-methyl-N-alkylpyrrolidinium, N-alkylpyridinium, N-alkyl-N-alkylpiperidinium, N-alkyl-N-alkylmorpholinium, tetraalkylammonium, tetraalkylphosphonium, N-methyl-N-oligoetherpyrrolidinium cations and BF₄⁻, CF₃BF₃⁻, CH₃BF₃⁻, CF₃SO₃⁻, PF₆⁻, dicyanamide, tricyanomethanide, tetracyanoborate, bis(trifluoromethane sulfonyl)imide (Ntf₂⁻ or TFSI⁻), bis(fluorosulfonyl)imide (FSI⁻) and nitrate anions. Classical molecular dynamics (MD) simulations have been performed on 30 ionic liquids at 298, 333, and 393 K. The IL density, heat of vaporization, ion self-diffusion coefficient, conductivity, and viscosity were found in a good agreement with available experimental data. Ability of the developed force field to predict ionic crystal cell parameters has been tested on four ionic crystals containing Ntf₂⁻ anions. The influence of polarization on the structure and ion transport has been investigated for [emim][BF₄] IL. A connection between the structural changes in IL resulting from turning off polarization and slowing down of ion dynamics has been found. Developed force field has also provided accurate description/prediction of thermodynamic and transport properties of alkanes, fluoroalkanes, oligoethers (1,2-dimethoxyethane), ethylene carbonate, propylene carbonate, dimethyl carbonate, hydrazine, methyhydrazine, dimethylhydrazine, acetonitrile, dimethyl amine, and dimethyl ketone.