A tongue in cheek observation would be that the Hartree-Fock model manages to build a determinant that has a little bit lower expectation value of the Hamiltonian, but it has to distort the orbitals (make them more diffuse) because the lowering of the kinetic energy then just outweighs the energy penalty of the increase in the electron-nuclear energy. The Hartree-Fock model does not care -it just tries to get the lowest energy determinant. As noted in contribution (2.2.12), the true power of Kohn-Sham DFT has to come from accurate approximations of the exchangecorrelation energy (defined in the Kohn-Sham context), but the good properties of the Kohn-Sham orbitals are an asset of this model.