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

The magnetic order of plutonium hydrides (PuH<sub><i>x</i></sub>) has long been a subject of controversy, both experimentally\nand theoretically. The magnetic, structural, electronic, and thermodynamic\nproperties of PuH<sub><i>x</i></sub> are investigated using\nHubbard-corrected density functional theory (DFT + <i>U</i>), with <i>U</i> derived from linear response calculations.\nTo address the issue of electronic metastable states within DFT + <i>U</i>, we employ an occupation matrix control method as well\nas allowing 5f orbitals to break the structural symmetry. This advanced\ncomputational approach establishes that the ground-state magnetic\norder for PuH<sub>2</sub> is antiferromagnetic and that for PuH<sub>3</sub> is ferromagnetic, consistent with Faraday and nuclear magnetic\nresonance experiments. Using the conventional hydrogen-vacancy model\nfor PuH<sub><i>x</i></sub>, the hydrogen-content-induced\nmagnetic transition and anomalous variation of the magnetic moment\nare successfully reproduced. In particular, the calculated transition\npoint of <i>x</i> matches the experimental findings. Furthermore,\nthe electronic configuration of the Pu atom in PuH<sub><i>x</i></sub> is determined to be 5f<sup>5</sup>, which is consistent with\nobservations from X-ray photoemission spectroscopy. Our calculated\nvalues for enthalpy of formation, heat capacity, and entropy are in\ngood agreement with experimental data, thereby validating the robustness\nof our theoretical framework.