(3.6.12) Baerends : In contribution (3.6.6), the "challenge" is put forward that, with the dissociating H 2 molecule as an example, one would never see any symmetry breaking if one employs the exact exchange-correlation functional within Kohn-Sham DFT. Actually, the dissociating H 2 molecule is a simple enough system that such a functional can be formulated. This functional becomes exact in the dissociation limit and does not lead to any symmetry breaking. Not unexpectedly, it is orbital dependent and employs in addition to the σ g orbital the σ u orbital. Since such involvement of "unoccupied" orbitals can be regulated via the natural orbital occupations, this ushers in reduceddensity-matrix-functional theory. For heavier systems, such functionals become approximate, but can still provide good dissociation curves without symmetry breaking. In the Kohn-Sham context, the temperature-assisted occupation DFT (TAO-DFT) of Chai 418 is an example of attempts to involve virtual Kohn-Sham orbitals via 1RDM-like occupation schemes.