Physical nature of intermolecular interactions in [BMIM][PF6] ionic liquid.

The intermolecular interaction energy in a popular ionic liquid, [BMIM][PF6] is analyzed using the Hybrid Variation-Perturbation Theory approach. The analysis is performed on a sample of configurations from molecular dynamics simulation, instead of minimized structures. The interaction energy components are quantified, showing that the electrostatics is the dominating but not the only important term. It is found that two- and three-body electron delocalization components also contribute to the stabilization of the complexes; however, these interactions vanish beyond the first coordination sphere. The presented study shows a systematic way to obtain the amount of physically meaningful components of the interaction energy, which possibly could be related to macroscopic properties of ionic liquids (e.g., viscosity, melting point) or electron transfer in ionic liquids.