Date of Award

2026-05-01

Degree Name

Master of Science

Department

Physics

Advisor(s)

Eunja Kim

Abstract

This thesis presents a first-principles investigation of uranium mononitride (UN), withemphasis on the connection between uranium 5f electron correlation and defect stability. Electronic-structure calculations were performed within density functional theory using the Vienna Ab initio Simulation Package. Exchange-correlation effects were treated within the generalized gradient approximation, and a Hubbard correction was applied to the uranium 5f manifold. The adopted Hubbard parameter was motivated by first-principles linear-response analysis and considered in the broader context of DFT+DMFT descriptions of correlated uranium systems, including recent interpretations of UN as a Hund-metal system. Bulk UN was studied in unit-cell and 2 x 2 x 2 supercell representations to establish a consistent antiferromagnetic reference state and to evaluate the effects of electron cor- relation and spin-orbit coupling. The results show that UN remains metallic within all treatments considered, while GGA+U redistributes uranium 5f states near the Fermi level and increases the calculated uranium magnetic moments. Using the relaxed antiferromagnetic supercell as the common reference, intrinsic point defects were examined through formation-energy calculations. The defect set included uranium and nitrogen vacancies, uranium and nitrogen interstitials, vacancy-pair configurations, and antisite defects. The calculated trends show that nitrogen interstitials and uranium vacancies are significantly stabilized within the GGA+U framework, while uranium interstitials become less favorable. Molybdenum and palladium incorporation was also investigated in substitutional and interstitial configurations. The incorporation energies show that Mo preferentially occupies uranium substitutional sites among the verified configurations, whereas Pd displays a stronger method dependence, with uranium-site substitution favored in GGA and tetrahedral interstitial incorporation favored in GGA+U. Overall, this work provides a consistent first-principles framework for understanding the role of uranium 5f correlation in bulk UN, intrinsic defect formation, and selected impurity accommodation.

Language

en

Provenance

Received from ProQuest

File Size

61 p.

File Format

application/pdf

Rights Holder

Roy Noe Herrera Navarro

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