DFT + U Study of Plutonium Hydrides with Occupation Matrix Control

Area of Science:

• Condensed Matter Physics
• Materials Science
• Computational Chemistry

Background:

• The magnetic order of plutonium hydrides (PuH_x) remains a contentious topic in scientific literature.
• Previous experimental and theoretical studies have yielded conflicting results regarding their magnetic properties.

Purpose of the Study:

• To computationally investigate the magnetic, structural, electronic, and thermodynamic properties of plutonium hydrides (PuH_x).
• To resolve the long-standing controversy surrounding the magnetic ordering in these compounds.

Main Methods:

• Employed Hubbard-corrected density functional theory (DFT + U), with U derived from linear response calculations.
• Utilized an occupation matrix control method and allowed 5f orbital symmetry breaking to address electronic metastable states.
• Investigated the hydrogen-vacancy model to understand hydrogen-content-induced magnetic transitions.

Main Results:

• Established antiferromagnetic ground-state order for PuH₂ and ferromagnetic order for PuH₃, consistent with experimental findings.
• Successfully reproduced hydrogen-content-induced magnetic transitions and anomalous magnetic moment variations.
• Determined the Pu atom's electronic configuration to be 5f⁵, aligning with X-ray photoemission spectroscopy data.

Conclusions:

• The advanced computational framework accurately predicts the magnetic order and properties of plutonium hydrides.
• The findings reconcile theoretical predictions with experimental observations, providing a robust understanding of PuH_x magnetism.
• Calculated thermodynamic properties (enthalpy of formation, heat capacity, entropy) show strong agreement with experimental data.