Single-particle and quasiparticle interpretation of Kohn-Sham and generalized Kohn-Sham eigenvalues for hybrid functionals

The quasiparticle interpretation of Kohn-Sham (KS) and generalized Kohn-Sham (GKS) eigenvalues is a frequently used tool to facilitate the analysis of experimental photoelectron spectra. Interpreting GKS eigenvalues from hybrid functionals is particularly popular for systems for which KS eigenvalues from semilocal functionals do not match experimental ionization potentials well. By calculating both KS and GKS eigenvalues for several organic semiconductor molecules, we demonstrate that the usually good interpretability of eigenvalues from hybrid functionals is mostly due to their numerical realization in the GKS scheme and not only due to their partial correction of self-interaction. Our results further illustrate why a stretching of the energy axis of KS spectra frequently but not always yields results that compare well to hybrid and experimental spectra.