Calculation of core-level electron spectra of ionic liquids

On the example of forty ion pairs, the study demonstrates how the core-level binding energy values can be calculated and used to plot theoretical spectra at a low computational cost using density functional theory methods. Three approaches for obtaining the binding energy values are based on delta Kohn–Sham (ΔKS) calculations, 1s Kohn–Sham orbital energies, and atomic charges. The ΔKS results show a good agreement between the available experimental X-ray photoelectron data. 1s Kohn–Sham orbital energies and atomic charges also correlate with the ΔKS results.