Comment on: ‘Failure of time-dependent density functional methods for excitations in spatially separated systems’ by Wolfgang Hieringer and Andreas Görling

Hieringer and Gِrling [W. Hieringer, A. Gِrling, Chem. Phys. Lett. 419 (2006) 557] have identified failures of time-dependent density functional theory (TDDFT) with standard spatially local functionals for symmetric systems with non-overlapping entities where zero net charge-transfer occurs. We clarify that this particular failure is a direct consequence of the general problem of charge-transfer nevertheless, in the special case of an exact degeneracy. The role of exact and accidental degeneracies in large systems treated by present-day TDDFT is briefly discussed.