Ab initio method was applied to investigate the interaction between six heterocyclic nitrogen compounds with 18 ionic liquids. Important quantum chemical descriptors like orbital energy values, orbital energy gap, and global scalar properties including hardness, softness, electronegativity, and electrophilicity index were calculated for each individual species, ionic liquid complexes, and complexes of ionic liquid with heterocyclic nitrogen compounds. The effect of interaction energy and partial charge transfer were also investigated for the ion pair and their complexes. COSMO-RS model is used for qualitative screening of the ionic liquids via sigma-profile and sigma-potential. Comparison between experimental and COSMO-RS predicted ternary tie-lines were done to validate computational method; good agreement was achieved with average RMSD less than 5%. From the results, ILs based on aromatic ring cations combined with either [EtSO4] or [Ac] anion are recommended as solvent for extractive denitrification of liquid fuels, with [EPY] [EtSO4] being the most favorable IL for removal of heterocyclic nitrogen compounds from liquid fuels at 298.15 K.