e Ligand-field DFT; present work. reported energies obtained with a larger active space but in restricted active-space (RAS) fashion. Calculations using a bare PuO 8 -system without and with PT2 corrections, as seen in Table in the SI, showed slight breaking of the state degeneracies in both CASSCF and NEVPT2 results in the absence of the embedding model (Table ). Furthermore, the embedding improves ΔE toward the experiment, and the calculated energies of the T 2 and E states relative to A from the present CAS(4,7) calculations improve toward the formally better RAS (12,16) calculation when the BR and PC regions are included in the model. Table also demonstrates that the state energies obtained from the LFDFT calculations are in overall in reasonable agreement with the MC-WFT results. This is an important check regarding the computational methodology, because later we present X-ray spectroscopic simulations using the LFDFT approach. Importantly, the present CAS(4,7)+SO and NEVPT2 calculations almost perfectly reproduce the magnetic susceptibility χ from the previous calculation as reported in Reference 6, as can be seen in Figure in the SI. Note that χ is slightly overestimated with respect to the experimental data and weakly temperature-dependent above 600 K, which was analyzed in Reference 6 and attributed to the involvement of electronic states deriving from ion levels other than 5 I 4 and their approximate description in the calculations. The experimental χ is near-quantitatively reproduced by calculations that only consider the states of 5 I 4 ion parentage in the calculation of χ; the relevant data are reproduced in Figure . Overall, the ground state and the lowenergy excited states of PuO 2 deriving from the 5 I 4 ion level are seen to be described well by the present MC-WFT calculations using the embedded cluster model.