(3.6.3) Vignale : With reference to contribution (3.6.2), a good case in point is that of open-shell atoms, where rotational symmetry demands the existence of a degenerate multiplet of ground states when the magnitude of the orbital angular momentum L is nonzero. There is no functional that I know that can guarantee that this degeneracy is respected when the densities of the degenerate states are not trivially related to each other by a rotation. Years ago, Becke attempted to solve this problem by introducing a current-dependent functional, but could not achieve rigorous degeneracy. 405 (3.6.4) Gould : It is worth noting that ensemble DFT, which invokes multiple Kohn-Sham states via ensemble density matrices, can restore all degeneracy. This is briefly discussed in Section 3.7.