DENSITY-FUNCTIONAL THEORY FOR EXCITED-STATES

Kohn-Sham formalism for the treatment of excited states within the den sity-functional theory (DFT) is presented. DFT exchange and correlatio n energy functionals for excited states are defined. Explicit expressi ons for these functionals are derived by generalizing a recent DFT per turbation theory. A computational scheme for the treatment of excited states within the DFT is suggested. Differences of Kohn-Sham eigenvalu es are shown to be well-defined approximations for excitation energies . Correction terms to these approximations are presented. Perturbation theory expansions for band gaps are discussed.