In the remainder of this Section, we examine the electronic structure and magnetism of PuO 2 as revealed by MC-WFT and DFT calculations complemented by a comprehensive set of X-ray absorption and emission spectroscopic data from M 5 -edge and M 3 -edge HR-XANES and VB-RIXS experiments along with Ligand-Field DFT calculations. The experimental spectroscopy results are shown to align closely with the theoretical findings.