In any case, these quantities correlate well enough with the largest errors in TD-DFT excitation energies so that one may define a "trust radius". It is suggested that states with Γ ≤ 1.8 Å for GGA functionals, or Γ ≤ 2.0 Å for global hybrids, are "safe" in the sense that the excitation energy in question is is unlikely to be seriously affected by long-range CT effects in TD-DFT. Since Γ ≈ d - e-h + d exc (insofar as the y ia amplitudes are small), this quantity provides not only a reliability metric for TD-DFT excitation energies but also a physically-interpretable numerical value for how charge moves (d - e-h ) and spreads (d exc ) upon excitation. For long-range excitations beyond 2.0 Å, it is suggested that the use of LRC functionals, or else global hybrids with at least 33% Hartree-Fock exchange, is mandatory. Finally, a "Mulliken-averaged configuration index" (MAC) has been suggested for detecting spurious low-energy CT states. (This is a slightly modified version of the metric called M AC that was proposed in Ref. 374, correcting what this author believes to be a typographical error.) The idea is that if ω < ω MAC , where ω is the excitation energy computed using TD-DFT, then the excited state in question is likely a "ghost" CT state, which should not be taken at face value. However, this metric should only be used for large values of d - e-h , because Mulliken's formula (on which it is based) makes sense only for large donor-acceptor separation. Moreover, given the crudeness of the approximation in Eq. (6.10), it is unclear how reliable this metric will be. As such, proper statistical measures of electron-hole correlation seem preferable.