Density Functional Theory for Excited States

Using the concept of entangled states it is shown that density functional theory in its initial ground-state formulation\footnote{P. Hohenberg and W. Kohn, Phys. Rev. \textbf{136}, B864, (1964).}$^,$\footnote{W. Kohn and L. J. Sham, Phys. Rev. \textbf{140}, A1133 (1965).}$^,$\footnote{M. Levy, Proc. Nat. Acad. Sci. USA \textbf{76}, 6062 (1979).} is inherently capable of treating the excited states of interacting many-particle systems.\footnote{\textbf{Acknowledgement}: Discussions with Mel Levy are gratefully acknowledged. This work was performed under the auspices of the U.S. Department of Energy under Contract DE-AC52-07NA27344 with LLNS, LLC. Work at ORNL was performed under the auspices of the Division of Materials Science and Engineering and at CNMS by the Division of Scientific User Facilities, Office of Basic Energy Science of the US Department of Energy.}