Using the present hybrid-functional DFT calculations with 20-50% eX as a guide, and considering that quantum chemical calculations may produce a more or less pronounced delocalization or localization error that impacts the extent of LM donation, it appears that in PuO 2 LM donation leads to an occupation around 1.1 to 1.2 of the 6d shell, and between about 1.4 to 1.6 excess occupation of the 5f shell when diffuse regions are considered. When the diffuse (5f') occupations are assigned as polarized ligand density instead, the excess of 5f occupation varies between 0.8 to 0.5 in the DFT calculations with 20-50% eX. Given that the spectroscopic n f from X-ray studies is subject to uncertainties related to the exact composition of the excited states that are being probed by the intensities, and given that the ground state n f extracted from calculations depends on the chosen density partitioning, an 5f-shell occupation around 5 in PuO 2 as assigned in Reference 7 is not incompatible with ab-initio calculations. This also means that the DFT calculations at the lower range of eX fraction are likely more reliable than the calculations with eX fractions around 50%. However, we reiterate that n f should not be confused with n open .