Orbitals obtained from the solution of the Kohn-Sham equations are also at the basis of most of many-body perturbation theories solving, in approximate manners, the Dyson and Bethe-Salpeter equations (GW and BSE methods). These approaches have brought tremendous progress in understanding properties of solids, in spite of some lack of accuracy, and almost all of them (for solids) are based on DFT.