Density functional theory from spherically symmetric densities: Ground and excited states of Coulomb systems

Recently, Theophilou J. Chem. Phys. 149, 074104 (2018) proposed a peculiar version of the density functional theory by showing that the set of spherical averages of the density around the nuclei determines uniquely the external potential in atoms, molecules, and solids. Here, this novel theory is extended to individual excited states. The generalization is based on the method developed in the series of papers by Ayers, Levy, and Nagy Phys. Rev. A 85, 042518 (2012). Generalized Hohenberg–Kohn theorems are proved to the set of spherically symmetric densities using constrained search. A universal variational functional for the sum of the kinetic and electron–electron repulsion energies is constructed. The functional is appropriate for the ground state and all bound excited states. Euler equations and Kohn–Sham equations for the set are derived. The Euler equations can be rewritten as Schrödinger-like equations for the square root of the radial densities, and the effective potentials in them can be expressed in terms of wave function expectation values. The Hartree plus exchange–correlation potentials can be given by the difference of the interacting and the non-interacting effective potentials.