Quantifying Local Atomic Distortions in UO₂ Grain Boundaries: Correlation with Energetic and Electronic Properties

Abstract

UO 2 , as a key material in the nuclear industry, is composed of grains or crystallites in real applications. Their interfaces, known as grain boundaries (GBs), significantly impact thermal conductivity, corrosion resistance, and mechanical response. Here, utilizing Hubbard-corrected density functional theory, we systematically examine the local cluster structures, energetic stabilities, and electronic properties of five typical tilt UO 2 GBs ranging from Σ 3 to Σ 11. We categorize all possible distorted U-and O-centered clusters at these GBs and identify their cluster morphologies and radial and angular distortions. Our results highlight the abundance of new U−O bonds stretching to "medium-range", a feature often overlooked in conventional coordination analysis. To quantitatively describe these distorted clusters, we use smooth overlap of atomic positions (SOAP) to represent the structural and chemical local environments, which takes into account both radial (2-body) and angular (3-body) distortions. We define a dissimilarity index by computing the inner product of SOAP descriptors between the distorted and the perfect motif in ideal UO 2 . Our findings show that the medium-range SOAP dissimilarity correlates well with the GB excess energy, outperforming metrics such as dangling bonds or bonding strain. Furthermore, it is found that the band gaps in sufficiently high-energy GBs are shortened, with excess states primarily contributed by the distorted U clusters. Our results present a comprehensive gallery of the local distorted clusters introduced by typical UO 2 GBs and have implications on the structure−property relations of GBs and other interfaces.

Adsorption, dissociation and diffusion behavior of H2O on the PuO2(111) surface from DFT + U-D3: the role of hydrogen bonding

“…22,23 The Hubbard model is used within the DFT + U method in the Dudarev formalism to treat strong on-site Coulomb interaction. 24 An effective U (U eff = U − J; i.e., the difference between the Coulomb U and exchange J parameters, hereaer referred to as U) value of 4 eV is selected for the 5f electrons of Pu and U, according to our previous calculations 25,26 and other computational experience. 10,12,14,18,20,[27][28][29] We use the widely accepted collinear 1-k antiferromagnetic (AFM) states along the (111) orientations for the magnetic orders.…”

Theoretical study on the hydrogen distribution and diffusion at the PuO2/α-Pu2O3 interface

“…28 An effective U ( U eff = U − J ; i.e. , the difference between the Coulomb U and exchange J parameters, hereafter referred to as U ) value of 4 eV is selected for the 5f electrons of Pu and U, according to our previous calculations 29,30 and other computational experience. 21,22,31–36 According to experimental and theoretical calculations (DFT + U ), the ground states of Pu 2 O 3 and PuO 2 are set to antiferromagnetic states (AFM).…”