Molecular Modelling of Ionic Liquids: Perfluorinated Anionic Species with Enlarged Halogen Substitutions

Ionic liquids as promising green solvents are widely applied in laboratory and industrial applications. Despite the massive experimental efforts on various applications, accurate computational modelling of such complex solution remains challenging. Our previous extensive numerical experiences on bulk properties, solvation and partition of external drug-like molecules between water and ionic-liquids phases lead to the recommended modelling regime of 0.8-scaled RESP charges and the GAFF2 parameter set. Such a protocol has been found to be effective in reproducing the experimental thermodynamic properties that require balanced descriptions of solute-solvent and solvent-solvent interactions. A deficiency in the previous benchmark set is the lack of voluminous and highly halogen-substituted anions. Therefore, in this work, we explore the calculation of ionic liquids involving large voluminous perfluorinated anionic species. Also, the ESP analysis confirms the similarity of the ESP produced by the gas-phase HF/6-31G* generated atomic charges and the higher-level implicit-solvent calculations. The quality of the HF/6-31G*-targeted charges is further validated by a direct face-to-face comparison of the bulk density estimated from molecular simulation under different charge sets, consolidating the protocol for model construction.