(2.2.21) Görling : It is instructive to define which electronicstructure approaches are Kohn-Sham methods. Such a definition reveals the key characteristics of the Kohn-Sham formalism and shows the scope and perspective that the Kohn-Sham formalism provides. By a quite wide definition, those methods are Kohn-Sham methods that rely on a model system of noninteracting 'electrons' with the same ground-state electron density as the true physical electronic system and with a local multiplicative potential. The noninteracting 'electrons' are particles that are identical to electrons -in particular, they have the spin of electronsbut do not interact among themselves. Given that the particles of the Kohn-Sham system are noninteracting, the Kohn-Sham equation for the Kohn-Sham orbitals and their eigenvalues in eqn (8) emerges immediately.