| Traditionally, density-functional theory (DFT) has been a theory of the ground state of a multi-electronic system. Although excited states were of concern since the beginning of DFT history, realistic calculational schemes have evolved only recently. The reason is that the techniques of ground-state DFT are not suitable enough for an adequate description of excited states. However, there are recent approaches to excited-state DFT that have turned out to be very promising in this notoriously difficult area.; The object is to find accurate approximations to excited-state energies and densities. In this dissertation several main approaches of modern excited-state DFT are reviewed, certain interrelation between them are revealed, and several new results announced.; Two universal functionals and are defined. By the use of constraint-search, the following property is proven: E0v<min F1r +&smallint;d 3vrr r r =E1v ≤E1v≤ E1v=min F1r +&smallint;d3rv rrr , 1 r where E0(v) and E1(v) are the round-state energy and the first excited-state energy, respectively, for a given external potential v(r). The minima in the above are achieved at the densities and , respectively.; Two universal tack-on functionals and are found. Once the minimizations are done in Eq. (1), they correct the minimizing values E1( v) and E1( v) to the exact first excited-state energy E 1(v), i.e. E1v=E 1v+F ′r1 2 and E1v=E 1v+F ′r1 , 3 |
