Getting the manifold right: The crucial role of orbital resolution in DFT+U for mixed d-f electron compounds

TL;DR

This paper demonstrates that precise disentanglement of localized and delocalized states using tailored projector functions significantly improves DFT+U predictions for complex actinide compounds, addressing longstanding modeling challenges.

Contribution

It introduces a method for optimizing orbital projectors in DFT+U to accurately model mixed d-f electron compounds, especially ternary monouranates.

Findings

Enhanced accuracy in electronic state predictions.

Corrected structural distortions in complex compounds.

Improved modeling of actinide solids.

Abstract

Accurately modeling compounds with partially filled $d$ and $f$ shells remains a hard challenge for density-functional theory, due to large self-interaction errors stemming from local or semi-local exchange-correlation functionals. Hubbard $U$ corrections can mitigate such errors, but are often detrimental to the description of hybridized states, leading to spurious force contributions and wrong lattice structures. Here, we show that careful disentanglement of localized and delocalized states leads to accurate predictions of electronic states and structural distortions in ternary monouranates (AUO$_4$, where A represents Mn, Co, or Ni), for which standard $U$ corrections generally fail. Crucial to achieving such accuracy is a minimization of the mismatch between the spatial extension of the projector functions and the true coordination geometry. This requires Wannier-like alternatives to atomic-orbital projector functions, or corrections of Hubbard manifolds exclusively comprised of the most localized A-$3d$, U-$5f$ and O-$2p$ orbitals. These findings open up the computational prediction of fundamental properties of actinide solids of critical technological importance.