Molecular Force Field for Ionic Liquids III: Imidazolium, Pyridinium, and Phosphonium Cations; Chloride, Bromide, and Dicyanamide Anions

This is the third set of parameters of a force field for the molecular simulation of ionic liquids, developed
within the spirit of the OPLS-AA model and thus oriented toward the calculation of equilibrium thermodynamic
and structural properties. The parameter sets reported here concern the cations alkylimidazolium, tetra-alkylphosphonium, and N-alkylpyridinium, and the anions chloride, bromide, and dicyanamide. The force
field is built in a stepwise manner that allows the construction of models for an entire family of cations, with
alkyl side chains of different length, for example. Due to the transferability of the present force field, the ions
studied here can be combined with those reported in our two previous publications to create a large variety
of ionic liquids that can be studied by molecular simulation. The parameters reported were obtained through
different series of ab initio calculations concerning the geometry, force constants, torsion energy profiles,
and electrostatic charge distributions of the ions under study. Validation of the force field consisted of
comparison with experimental crystal structure and liquid density data.