Molecular dynamics study of the ionic liquid 1-n-hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([C6C1im][FAP]): Force field development and the effect of [FAP]− isomer content on properties

A new all-atom force field for the tris(pentafluoroethyl)trifluorophosphate ([FAP]−) anion was developed and paired with an existing force field for 1-n-hexyl-3-methylimidazolium ([C6C1im]+). Molecular dynamics simulations were employed to compute the density, shear viscosity, self-diffusivity, local dynamics, and liquid structure of [C6C1im][FAP]. Computed densities, isothermal compressibility, isobaric expansivity, and shear viscosities all agree well with experimental data. The octahedral geometry of the [FAP]− anion results in facial ([fFAP]−) and meridional ([mFAP]−) isomers. Simulations with varying ratios of the two [FAP]− isomers show modest but non-negligible differences in properties as a function of isomer composition