Accurate prediction of ionic liquid density-of-states from low-cost calculations

The electronic structure of ionic liquids (ILs) is a key factor in their chemical reactivity. Experimental techniques provide insight into IL electronic structure (<i>e.g</i>., X-ray photoelectron spectroscopy, XPS), but are impractical for screening large numbers of potential ILs. Computational screening offers an alternative approach, but current <i>ab initio</i> calculation methods (ion-pairs or large calculations with periodic boundaries) are not suitable for screening. We establish that a simple and computationally low-cost method, lone-ions evaluated at the B3LYP-D3(BJ)/6-311+G(d,p) level employing a generalised solvation model SMD (solvation model based on density), captures IL liquid-phase density-of-states (DoS) with good accuracy by validating against XPS data for a wide range of ILs. The additivity of the results from individual lone-ion calculations provides a significant advantage, enabling predictions of the DoS for a large number of ILs and delivering a significant step towards the computational screening of ILs for many applications.