(3.2.15) Neese : I very much welcome this discussion. In practice, there is a large self-interaction error (SIE). This error is large and profoundly influences the localization/delocalization of the Kohn-Sham orbitals and consequently, the properties derived from them and the associated electron density. We know that removing the SIE using established methods like the Perdew-Zunger scheme 10 destroys much of the accuracy of Kohn-Sham DFT. The development of physically based correlation functionals becomes challenging with this error in the background.