Insight on the oxidation resistance of UO N layers: A density functional study

Chemical State of U in U–N–O Ternary System from First-Principles Calculations

“…The strong on-site Coulomb repulsion among the localized U 5f electrons was described by using the Hubbard U correction (DFT + U ) developed by Dudarev et al, which has shown success in many U-based intermetallic alloys . It is well believed that an U eff value of >1.80 eV is necessary to accurately describe the structural and magnetic properties of uranium nitrogen compounds .…”

“…The strong on-site Coulomb repulsion among the localized U 5f electrons was described by using the Hubbard U correction (DFT + U) developed by Dudarev et al, 38 which has shown success in many U-based intermetallic alloys. 10 It is well believed that an U eff value of >1.80 eV is necessary to accurately describe the structural and magnetic properties of uranium nitrogen compounds. 39 In this paper, we used the Hubbard and exchange parameters of effective U of U eff = 4.0 eV for all the calculations, on the basis of the fact that the valence state of U atoms in UN is significantly lower than 3.0 using U eff = 1.0, 2.0, 3.0, and 6.0 eV, which is inconsistent with the formal valence state of U 3+ for UN.…”

“…Interestingly, when the temperature exceeded 573 K, O in UN 1.66 and UN 1.42 O 0.23 films decreased significantly, whereas N increased due to the diffusion of N from the inner to outer layer. These findings suggest a diversified chemical formula of UN x O y , as evidenced by electron-energy-loss spectroscopy and first-principles calculations . Recently, Jin et al investigated the geometric, magnetic, electronic, and vacancy properties of bulk α-U 2 N 3 through first-principles calculation within DFT + U framework, as well as its reaction with oxygen .…”

“…The third one is the argument on the magnetic properties of UN 2 and α-U 2 N 3 , which is also related to the controversy between metal and semiconductor. It has been argued that the stoichiometric UN 2 is not dynamically and energetically stable due to the presence of imaginary frequencies in phonon dispersion and minus enthalpy of formation for N vacancy. , Lu et al calculated the total energies of ferromagnetic (FM), antiferromagnetic (AFM), and nonmagnetic (NM) UN 2 phases and found that the lowest-energy magnetic state is NM . Recently, ab initio quantum chemical calculations were employed to investigate the electronic, mechanical, elastic, and thermodynamic properties of FM UN 2– x using GGA + U (with a Hubbard U of 2 eV) .…”

“…These findings suggest a diversified chemical formula of UN x O y , as evidenced by electron-energy-loss spectroscopy 9 and first-principles calculations. 10 Recently, Jin et al investigated the geometric, magnetic, electronic, and vacancy properties of bulk α-U 2 N 3 through first-principles calculation within DFT + U framework, as well as its reaction with oxygen. 11 They found that the formation of N (U) single vacancy inα-U 2 N 3 is almost spontaneous under U-rich (Orich) conditions and the energy barriers for oxygen diffusion through α-U 2 N 3 layers are larger than 1. reaction, as manifested in their ab initio molecular dynamics simulations, in line with X-ray photoelectron spectroscopy (XPS) experimental findings.…”