be viewed more as a donation-like polarization of ligand electron density rather than a bona fide density transfer, but this qualifier only highlights the fact that there is no unique partitioning of the electron density into atomic shell contributions especially in the diffuse regions of the atoms. For PuO 2 , the donation into the formally empty 6d shell is considerable, exceeding 1 electron in all of the calculations. Minor 7s occupations are also present, as are minor occupations (approx. 0.2 combined) of other outer Pu shells (7p, 7d, and others), which are not listed separately. The calculated partial plutonium charge from the NPA is q(Pu). Therefore, 4-q(Pu) in Table is the total LM donation when accounting for the four unpaired electrons of the metal ion, including donation into the aforementioned outer shells that are not listed explicitly. The combined excess 5f (+ 5f'), 6d, and 7s occupation tracks the total donation closely. Across the range of eX fractions in the functional, the 6d occupation varies comparatively little (between 1.21 and 1.02), the NPA 5f occupation varies strongly (between 5.02 and 4.26 total, between 1.02 and 0.26 excess), and the 5f' occupation varies modestly between 0.71 to 0.96. In aggregate, therefore, the 5f-shell excess electron count (NPA 5f + 5f') varies considerably as a function of the electronic structure model, between 1.73 and 1.22 for the PBE-based functionals with 0-100% eX, and 1.25 for the spin-unrestricted HF calculation.