Linear tricationic ionic liquids: Insights into the structural features using DFT and molecular dynamics simulation

Abstract

In this study, three imidazolium-based linear tricationic ionic liquids (LTILs) have been studied using density functional theory (DFT) and also classical molecular dynamics simulation (MDS) to gain a deeper insight into their structures. Geometrical counterpoise (gcp) and D3 corrections were used to correct the electronic energies of the studied ions and LTILs and to interpret the unusual trends in their physical properties, i.e. their viscosities and melting points. To investigate the contributions of hydrogen bonds, dispersion interactions and steric effects to binding energies of LTILs, the NCI method which is based on the calculation of reduced density gradient (RDG) was used. The natural bond orbital (NBO) analysis has been also employed to study the H-bonding in the studied LTILs. A helical structure for the cations of the studied LTILs was observed as a result of strong network of different types of Hydrogen bonds. A non-polarizable all atom force field which is a refined version of Canongia Lopes and Paudua (CL&P) was adopted for the simulations. As well as the heterogeneity order parameter (HOP), the angular distribution functions of the angles of LTIL molecules have been used to describe the heterogeneity and spatial structure of the studied LTILs. The structural organization of the LTILs has been also compared with corresponding mono- and di-cationic ILs (MILs and DILs).