Communication: Kohn-Sham theory for excited states of Coulomb systems

For obtaining individual excited-state energies and densities of Coulomb electronic systems, by means of an energy stationary principle, it was shown previously that there exists a universal functional of the density, F(Coul)ϱ, for the kinetic plus electron-electron repulsion part of the total energy. Here, we make knowledge of the existence of F(Coul)ϱ practical for calculation by identifying Ts (Coul)ϱ, the non-interacting kinetic energy component of F(Coul)ϱ, and by showing that Ts (Coul)ϱ may be computed exactly by means of orbitals that are obtained through a set of single-particle Kohn-Sham equations. Constraints for obtaining accurate approximations to the remaining unknown component of F(Coul)ϱ are presented.