Electronic and optical excitations from screened range-separated hybrid density functional theory

Some ten years ago, we have introduced the concept of optimal tuning (OT) of range-separated hybrid (RSH) functionals as a means of overcoming the fundamental gap problem and the charge transfer excitation problem in molecular systems. Here, this concept is extended to the solid state by introducing dielectric screening into the functional form. This approach, couched rigorously within the generalized Kohn-Sham formalism of density functional theory, can produce quantitatively the same one and two quasi-particle excitation picture given by many-body perturbation theory. Specifically, for molecular solids the approach predicts the correct gap renormalization without any empiricism. This can be achieved even from single molecule calculations if a polarizable continuum model is combined with the screened OT-RSH calculation in an electrostatically consistent manner. For covalent/ionic semiconductors and insulators, one empirical parameter is set to reproduce the direct bandgap. Accurate band structures and optical absorption spectra, which agree well with those obtained from GW and GW-BSE calculations, respectively, are then obtained.