(3.2.16) Baerends : To further this discussion, let me note that it is indeed generally accepted that the origin of the poor orbital energies of presently available DFAs are the unphysical selfinteractions. However, it is not completely clear what is meant by SIE. The one-electron SIE is felt to be evident: the exchangecorrelation energy of a one-electron system like the H atom (in this case just the exchange energy) should cancel the Hartree energy. Actually, LDA is not so bad for the H atom: the Hartree energy of 8.01 eV is cancelled to a reasonable degree by the LDA exchange energy of -6.89 eV, yielding an error of only 1.12 eV. If we add the B88 GGA gradient correction for the exchange energy, then the SIE is reduced to 0.04 eV. The same very small SIE is observed for the H 2 molecule at the equilibrium distance. This should give us pause for thought when we want to blame the SIE for failures of DFAs. How much SIE is there really in the current DFAs? The DFA error in the orbital energy is of a different order of magnitude: 6.88 eV above the exact H-atom value with LDA and 6.20 eV when the B88 gradient correction is addedclearly, not the same effect as the tiny SIE in the total energy. The effect on the orbital energies that we call SIE arises when we take the functional derivative of the energy (it is in v resp ).