A quantum mechanical study of alkylimidazolium halide ionic liquids

► The ions composed of one alkylimidazolium cation and 2-3 halogen anions were studied. ► The models studied are more consistent with crystal results than ion pair systems. ► A linear correlation between melting point Tm and interaction energy ΔE was observed. ► The Tm-ΔE correlation is consistent with that of amino acid cation based ILs. ► Our Letter shows the potential for quantum chemical calculations to predict Tm of ILs.