Atomistic Force Field for Pyridinium-Based Ionic Liquids: Reliable Transport Properties

Reliable
force field (FF) is a central issue in successful prediction
of physical chemical properties via computer simulations. This work
introduces refined FF parameters for six popular ionic liquids (ILs)
of the pyridinium family (butylpyridinium tetrafluoroborate, bis­(trifluoromethanesulfonyl)­imide,
dicyanamide, hexafluorophosphate, triflate, chloride). We elaborate
a systematic procedure, which allows accounting for specific cation–anion
interactions in the liquid phase. Once these interactions are described
accurately, all experimentally determined transport properties can
be reproduced. We prove that three parameters per interaction site
(atom diameter, depth of potential well, point electrostatic charge)
provide a sufficient basis to predict thermodynamics (heat of vaporization,
density), structure (radial distributions), and transport (diffusion,
viscosity, conductivity) of ILs at room conditions and elevated temperature.
The developed atomistic models provide a systematic refinement upon
the well-known Canongia Lopes–Pádua (CL&P) FF. Together
with the original CL&P parameters the present models foster a
computational investigation of ionic liquids.