$\textit{Ab initio}$ downfolding based on the GW approximation for infinite-layer nickelates

TL;DR

This paper develops an effective three-orbital model for infinite-layer nickelates using GW approximation, revealing increased correlation effects and Mott-Hubbard character compared to LDA-based models.

Contribution

It introduces a GW-based ab initio downfolding method for nickelates, highlighting the impact of self-energy corrections on electronic structure and correlations.

Findings

GW approximation increases Ni 3d-2p energy difference

Bandwidth of antibonding 3d_{x^2-y^2} orbitals is reduced

Correlation effects and Mott-Hubbard character are enhanced

Abstract

We derive an effective three-orbital model for the infinite-layer nickelates based on the band structure obtained by the GW approximation (GWA), where we consider the Ni 3$d_{x^2-y^2}$ and O 2$p$ orbitals forming the $\sigma$-bond. In the GWA, the self-energy correction to the local density approximation (LDA) increases the energy difference between Ni $3d_{x^2-y^2}$ and O $2p$, which reduces the bandwidth of the antibonding 3$d_{x^2-y^2}$ orbitals. The isolation of the Ni $3d_{x^2-y^2}$ around the Fermi level suppresses the screening effect. As a result, the correlation effect becomes more significant than that in the model constructed by the LDA-based downfolding. Furthermore, the Mott-Hubbard type character is enhanced in the GWA-based effective model, because the charge-transfer energy increases more rapidly compared to the increase in the interaction parameters.