Exploring Metastable States in UO$_2$ using Hybrid Functionals and Dynamical Mean Field Theory

TL;DR

This paper investigates the complex energy landscape of UO$_2$ using advanced first-principles methods, revealing multiple metastable states with lower energies than previously known, enhancing understanding of its electronic properties.

Contribution

It introduces a hybrid functional approach combined with DMFT to explore metastable states in UO$_2$, showing a richer energy landscape than previously understood.

Findings

Discovery of multiple metastable electronic states in UO$_2$

Identification of states with energies lower than prior ground states

Demonstration of the complex energy landscape of f-electron oxides

Abstract

A detailed exploration of the $f$-atomic orbital occupancy space for UO$_2$ is performed using a first principles approach based on density functional theory (DFT), employing a full hybrid functional within a systematic basis set. Specifically, the PBE0 functional is combined with an occupancy biasing scheme implemented in a wavelet-based algorithm which is adapted to large supercells. The results are compared with previous DFT+U calculations reported in the literature, while dynamical mean field theory (DMFT) is also performed to provide a further base for comparison. This work shows that the computational complexity of the energy landscape of a correlated $f$-electron oxide is much richer than has previously been demonstrated. The resulting calculations provide evidence of the existence of multiple previously unexplored metastable electronic states of UO$_2$, including those with energies which are lower than previously reported ground states.