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Impact of the U parameter on the predicted defect chemistry of materials: The example of PuO2±x

Reece Bedford* and Samuel Murphy†

Hayley Green

Sophie Cooper and Robin Orr

William Neilson and Michael W. D. Cooper

  • *Contact author: r.t.bedford@lancaster.ac.uk
  • †Contact author: samuel.murphy@lancaster.ac.uk
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Phys. Rev. Materials 10, 065403 – Published 11 June, 2026

DOI: https://doi.org/10.1103/w8xw-ghmh

Abstract

Density functional theory (DFT) provides a powerful tool for describing the electronic properties of materials, however, self-interaction errors in semilocal functionals complicate the accurate modeling of correlated materials. The DFT+U method is a popular and computationally cost-effective solution for mitigating self-interaction; though, this reduces the ab initio aspect of DFT calculations, as the outcome now becomes dependent on the user's choice of U parameters. Atomistic modeling of plutonium dioxide (PuO2) is employed to provide insight into its evolution in storage or into its properties as mixed-oxide fuel. There is no single U parameter that can reproduce all the experimental properties of PuO2 accurately and, as such, it is important that the U parameter is selected with careful consideration. In this work, we use noncollinear DFT+U simulations to thoroughly examine the defect chemistry of PuO2 using U=4 and 7eV, in order to understand the implication the choice of U parameter can have on the predicted defect chemistry. We find that both U parameters predict the same intrinsic defect chemistry, with the main discrepancy being on the preferred charge state of the oxygen vacancies: +2 for U=4eV and neutral for U=7eV. Additionally, we show that the choice of U can impact the defect formation energies and preferred charge states of a dopant. When uranium is placed onto a plutonium lattice site, it tends to favor the neutral and +1 charge state (indicative of U4+ and U5+) with U=4eV, whereas with U=7eV the −1 and neutral charge states are more stable.

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Phys. Rev. Materials 10, 065403– Published 11 June, 2026
  • Received 20 June 2025
  • Revised 4 March 2026
  • Accepted 2 April 2026
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