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Open AccessArticle

The Conundrum of Relaxation Volumes in First-Principles Calculations of Charged Defects in UO2

1
Department of Materials Science and Engineering, University of Florida, Gainesville, FL 32611, USA
2
Department of Physics, Missouri University of Science and Technology, Missouri University of Science and Technology, Rolla, MO 65409, USA
3
Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA
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Engineering Department, Lancaster University, Bailrigg, Lancaster LA1 4YW, UK
*
Author to whom correspondence should be addressed.
Current Address: Metallurgical and Materials Engineering, Colorado School of Mines, Golden, CO 80401, USA.
Appl. Sci. 2019, 9(24), 5276; https://doi.org/10.3390/app9245276
Received: 12 November 2019 / Revised: 29 November 2019 / Accepted: 1 December 2019 / Published: 4 December 2019
The defect relaxation volumes obtained from density-functional theory (DFT) calculations of charged vacancies and interstitials are much larger than their neutral counterparts, seemingly unphysically large. We focus on UO2 as our primary material of interest, but also consider Si and GaAs to reveal the generality of our results. In this work, we investigate the possible reasons for this and revisit the methods that address the calculation of charged defects in periodic DFT. We probe the dependence of the proposed energy corrections to charged defect formation energies on relaxation volumes and find that corrections such as potential alignment remain ambiguous with regards to its contribution to the charged defect relaxation volume. We also investigate the volume for the net neutral defect reactions comprising individual charged defects, and find that the aggregate formation volumes have reasonable magnitudes. This work highlights the issue that, as is well-known for defect formation energies, the defect formation volumes depend on the choice of reservoir. We show that considering the change in volume of the electron reservoir in the formation reaction of the charged defects, analogous to how volumes of atoms are accounted for in defect formation volumes, can renormalize the formation volumes of charged defects such that they are comparable to neutral defects. This approach enables the description of the elastic properties of isolated charged defects within an overall neutral material. View Full-Text
Keywords: defects; elasticity; relaxation volume; dipole tensor; urania; density functional theory defects; elasticity; relaxation volume; dipole tensor; urania; density functional theory
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Goyal, A.; Mathew, K.; Hennig, R.G.; Chernatynskiy, A.; Stanek, C.R.; Murphy, S.T.; Andersson, D.A.; Phillpot, S.R.; Uberuaga, B.P. The Conundrum of Relaxation Volumes in First-Principles Calculations of Charged Defects in UO2. Appl. Sci. 2019, 9, 5276.

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