DFT + <i>U</i> Study of Plutonium Hydrides with Occupation Matrix Control

The magnetic order of plutonium hydrides (PuH_<i>x</i>) has long been a subject of controversy, both experimentally and theoretically. The magnetic, structural, electronic, and thermodynamic properties of PuH_<i>x</i> are investigated using Hubbard-corrected density functional theory (DFT + <i>U</i>), with <i>U</i> derived from linear response calculations. To address the issue of electronic metastable states within DFT + <i>U</i>, we employ an occupation matrix control method as well as allowing 5f orbitals to break the structural symmetry. This advanced computational approach establishes that the ground-state magnetic order for PuH₂ is antiferromagnetic and that for PuH₃ is ferromagnetic, consistent with Faraday and nuclear magnetic resonance experiments. Using the conventional hydrogen-vacancy model for PuH_<i>x</i>, the hydrogen-content-induced magnetic transition and anomalous variation of the magnetic moment are successfully reproduced. In particular, the calculated transition point of <i>x</i> matches the experimental findings. Furthermore, the electronic configuration of the Pu atom in PuH_<i>x</i> is determined to be 5f⁵, which is consistent with observations from X-ray photoemission spectroscopy. Our calculated values for enthalpy of formation, heat capacity, and entropy are in good agreement with experimental data, thereby validating the robustness of our theoretical framework.