Ground-State Energy as a Simple Sum of Orbital Energies in Kohn-Sham Theory: A Shift in Perspective through a Shift in Potential

It is observed that the exact interacting ground-state electronic energy of interest may be obtained directly, in principle, as a simple sum of orbital energies when a universal density-dependent term is added to w([rho];r), the familiar Hartree plus exchange-correlation component in the Kohn-Sham effective potential. The resultant shifted potential, (w) over bar ([rho]; r), actually changes less on average than (w) over bar([rho];r) when the density changes, including the fact that (w) over bar([rho];r) does not undergo a discontinuity when the number of electrons increases through an integer. Thus, the approximation of (w) over bar([rho];r) represents an alternative direct approach for the approximation of the ground-state energy and density.