Lastly, the pronounced ligand to metal donation prevailing in PuO 2 is also revealed by DFT calculations with periodic boundary conditions. Although it is widely known to the community that semi-local functionals do not provide a qualitative correct description of the electronic structure of actinide dioxides, in agreement with recent work, our DFT+U calculations using PBESol functional and including SOC generate the expected insulating nonmagnetic ground state for PuO 2 . The corresponding band structure (shown in Figure ) reveals a band gap of 1.8 eV in agreement with previous studies. The computed DOS (shown in Figure ) reveals sizable hybridization of Pu f-states with O p-states near Fermi level, which is a clear indicator of significant ligand to metal donation in PuO 2 . The periodic DFT+U calculations therefore agree with the assignment n open = 4, n f > 4, and a 5f 4 Pu(IV) electron configuration.