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.