New quantum chemistry-based descriptors for better prediction of melting point and viscosity of ionic liquids

Ionic liquids (ILs) are chemicals that are nonvolatile and hence have the potential to replace volatile organic compounds in industrial applications. A large number of ILs, through the combination of different cations and anions, can potentially be synthesized. In this context, it will be useful to intelligently design customized ILs through computer-aided methods. Practical limitations dictate that any successful attempt to design new ILs for industrial applications requires the ability to accurately predict their melting point and viscosity as experimental data will not be available for the designed structures. In this paper, we present two new correlations for precise prediction of melting point and viscosity of ILs solely based on inputs from quantum chemistry calculations (no experimental data or simulation results are needed). To develop these correlations we utilized data related to size, shape, and electrostatic properties of cations and anions that constitutes ILs. In this work, new descriptors such as dielectric energy of cations and anions as well as the values predicted by an 'ad-hoc' model for the radii of cations and anions (instead of their van der waals radii) were used. A large number of correlation equations consisting different combination of descriptors (as inputs to the model) were tested and the best correlation for viscosity and melting point were identified. The average relative errors were estimated as 3.16% and 6.45% for melting point, Tm, and ln(vis), respectively.