Energetics of the coupled electronic-structural transition in the rare-earth nickelates

TL;DR

This study combines advanced computational methods to elucidate the complex interplay between structural distortions and electronic correlations driving the metal-insulator transition in rare-earth nickelates.

Contribution

It introduces a charge self-consistent DFT+DMFT approach with RPA-derived interactions to accurately model coupled electronic-structural transitions.

Findings

Electronic instability stabilizes structural distortion.

Octahedral rotations suppress electronic instability.

Correlation effects weaken across the series.

Abstract

Rare-earth nickelates exhibit a metal-insulator transition accompanied by a structural distortion that breaks the symmetry between formerly equivalent Ni sites. The quantitative theoretical description of this coupled electronic-structural instability is extremely challenging. Here, we address this issue by simultaneously taking into account both structural and electronic degrees of freedom using a charge self-consistent combination of density functional theory and dynamical mean-field theory, together with screened interaction parameters obtained from the constrained random phase approximation. Our total energy calculations show that the coupling to an electronic instability towards a charge disproportionated insulating state is crucial to stabilize the structural distortion, leading to a clear first order character of the coupled transition. The decreasing octahedral rotations across the series suppress this electronic instability and simultaneously increase the screening of the effective Coulomb interaction, thus weakening the correlation effects responsible for the metal-insulator transition. Our approach allows to obtain accurate values for the structural distortion and thus facilitates a comprehensive understanding, both qualitatively and quantitatively, of the complex interplay between structural properties and electronic correlation effects across the nickelate series.