First principles calculations for defects in U

Abstract

Uranium (U) exhibits a high temperature body-centered cubic (bcc) allotrope that is often stabilized by alloying with transition metals such as Zr, Mo, and Nb for technological applications. One such application involves U-Zr as nuclear fuel, where radiation damage and diffusion (processes heavily dependent on point defects) are of vital importance. Several systems of U are examined within a density functional theory framework utilizing projector augmented wave pseudopotentials. Two separate generalized gradient approximations of the exchange-correlation are used to calculate defect properties and are compared. The bulk modulus, the lattice constant, and the Birch-Murnaghan equation of state for the defect free bcc uranium allotrope are calculated. Defect parameters calculated include energies of formation of vacancies in the α and γ allotropes, as well as self-interstitials, Zr interstitials, and Zr substitutional defects for the γ allotrope. The results for vacancies agree very well with experimental and previous computational studies. The most probable self-interstitial site in γ-U is the (110) dumbbell, and the most probable defect location for dilute Zr in γ-U is the substitutional site. This is the first detailed study of self-defects in the bcc allotrope of U and also the first comprehensive study of dilute Zr defects in γ-U.

Atomistic modeling of the self-diffusion in γ-U and γ-U-Mo

“…The magnitude of for γ U found in MD mod eling turns out to be overestimated compared with the values found from static calculations by the DFT method [37,38] and from the positron annihilation vac SIA 1 1 1 ; [39,40]. The magnitudes of are within the energy range evaluated for interstials from static calculations in the DFT scope, i.e., from 0.5 to 1.5 eV [38] depending on the defect configuration.…”

Comment on “Correlation and relativistic effects in U metal and U-Zr alloy: Validation ofab initioapproaches”

“…However, there is a wealth of studies implying the opposite [4][5][6][7][8][9][10][11][12][13][14][15], namely that neither DFT+U nor SOC are necessary for an accurate description of uranium metal or its alloys with zirconium. We argue that the DFT+U approach for these systems leads to inconsistencies and inaccurate results for formation enthalpies, atomic volumes, and magnetic properties and should best be avoided, contrary to the conclusion of [1] where it is argued to be an improvement over conventional DFT.…”

New interatomic potential for computation of mechanical and thermodynamic properties of uranium in a wide range of pressures and temperatures

“…Table 5. Energy of vacancy formation in γ U, eV EAM MD [19] 1.75 ab initio [8] 1.08 ab initio [9] 1.384 Experiment [34] 1.20 ± 0.25 New EAM potential 1.52…”

“…Xiang, Huang, and Hsiung [8], also used the pseudopotential method to calculate the properties of defects for the uranium-niobium system (including single vacancies in uranium). The results of a detailed analysis of possible defects (vacancies, inter stitial atoms) in the uranium crystalline phases are given in [9]. The authors determined, in terms of the density functional theory (using a pseudopotential), the energies of vacancy formation in uranium crystal line phases, as well as the hierarchy of the energies of formation of possible defects in γ U.…”