Infrared and Raman signatures of stoichiometric PuO₂: A density functional theory study

A comprehensive understanding of the vibrational signatures of PuO₂ is essential for analysing its defect chemistry and ageing, and for establishing the provenance of unknown material. The ground-state magnetic ordering of PuO₂ is still under debate, with experiments and theory predicting diamagnetic (DM) and longitudinal 3k antiferromagnetic (LAFM-3k) states with the same cubic Fm3¯m symmetry. In this work, we employ periodic density functional theory incorporating spin-orbit interactions and noncollinear magnetism to explore how magnetic structure influences the structural dynamics of PuO₂. We find that the DM and LAFM-3k structures show similar infrared (IR) and Raman features, whereas other magnetic orderings, including the 1k AFM structure widely used in computational studies, lead to symmetry breaking and a characteristic peak splitting due to loss of band degeneracy. These results underscore the importance of an accurate description of the magnetic structure when modelling PuO₂ and suggest that vibrational spectroscopy could serve as a sensitive probe of the local magnetic ordering.