A general definition of SIE is not so easy to formulate. In the original Perdew-Zunger work, the total energy was taken as starting point for constructing the correction. The most important effect of the Perdew-Zunger correction was, however, to change the potential and most of their discussion was focused on orbital energies. A straightforward definition of the SIE (also in the many-electron case) would be the error incurred by the exchange-correlation hole not integrating to -1 electron. Now, the first exact property that is required of the model holes in DFT is that they do integrate to -1 electron, as is already true for Slater's ρ 1/3 approximation. This does indeed lead to reasonable results for the total energy but does not guarantee a good potential because of deficiencies that appear in the step to the corresponding potential. Using exact exchange (100% or at least a very large percentage) in either a generalized Kohn-Sham or EXX-OEP manner also provides a large improvement in the orbital energies, as noted in contribution (3.2.14). The improvement is due to the way the step to the potential works out in that case, as it does for the Hartree-Fock-like correction in the Perdew-Zunger selfinteraction correction.