Generalized density functional theory - Comment

The density functional formalism of Hohenberg, Kohn and Sham can be applied only to the calculation of the ground-state properties of the system. In general, the energy of the electronic excitations can be obtained from the self-energy operator Sigma(r, r', omega), which requires a much larger computational effort. Recently, Fritsche has proposed a generalization of the density functional theory to excited states, that has been applied to the calculation of the band gaps of solid rare gases, alkali halides, diamond and silicon. We show that Fritsche's theory is incorrect since it is in strong disagreement with the Kohn-Sham theory when the ground state properties are considered.