The impact of intrinsic H defects and O impurities on the properties of PuH2: A DFT and machine learning force field study

• The formation of substitutional oxygen atoms in PuH 2 is always energetically favorable. • The introduction of SOC and defects will drastically alter the electronic density of states distribution in PuH 2 . • Hydrogen vacancies accelerate the diffusion of hydrogen atoms in plutonium hydrides, whereas interstitial hydrogen atoms and oxygen impurities restrict hydrogen diffusion. The inherent radioactivity of plutonium facilitates the formation of point defects, such as vacancies, in its common corrosion product PuH 2 , thereby affecting fuel performance. Using density functional theory (DFT) with explicit inclusion of spin–orbit coupling (SOC), this study systematically investigates the structural, electronic, and bonding properties of defective PuH 2 . The defects considered include intrinsic hydrogen defects and oxygen impurities substituting for hydrogen. The inclusion of SOC significantly affects defect formation energies: without SOC, PuH 2 exhibits a high electronic density of states above the Fermi level, a feature markedly suppressed upon introducing SOC or point defects. When temperature effects are incorporated, the point defect formation energies align closely with the static DFT + SOC results. Within the studied defect concentration range (3.125% to 12.5% of Pu atoms), hydrogen vacancies enhance hydrogen diffusivity, whereas interstitial hydrogen and oxygen doping inhibit it. This study provides theoretical insights for mitigating hydrogen-induced corrosion in plutonium-based materials.