The intermolecular interactions between the anions and cations of ionic liquids are the most important factors that dictate the transport properties of such liquids. Ab initio molecular orbital calculation methods are becoming a method of choice for the investigation of intermolecular interaction energies . So far as large basis set is used, and electron correlation is properly implemented, ab initio calculations could provide accurate interaction energies . Aiming at investigating the molecular interactions and the occurrence of Hbonding in [FSI] ion pairs, the interaction energy of the different ion pair conformations were calculated using ωB97x-D/DGDZVP level of theory and basis set in the presence of acetonitrile as a solvent. The interaction energy between the cation and the anion of the ILs was calculated according to the following expression: