Metal-Insulator Transition and the Role of Electron Correlation in FeO2

TL;DR

This study investigates the electronic and structural properties of FeO2 under mantle conditions, revealing a correlation-driven metal-insulator transition influenced by pressure and Coulomb interactions, crucial for understanding Earth's deep lower mantle.

Contribution

The paper combines DFT and DMFT methods to demonstrate how electron correlations induce a metal-insulator transition in FeO2, highlighting the importance of Coulomb interactions and pressure effects.

Findings

FeO2 has a structure with Fe2+ and O2 2- dimers.

The O2 dimer bond length is sensitive to Coulomb U, affecting electronic properties.

Metal-insulator transition is driven by U and pressure changes.

Abstract

Iron oxide is a key compound to understand the state of the deep Earth. It has been believed that previously known oxides such as FeO and Fe2O3 will be dominant at the mantle conditions. However, recent observation of FeO2 shed another light to the composition of the deep lower mantle (DLM) and thus understanding of the physical properties of FeO2 will be critical to model DLM. Here, we report the electronic structure and structural properties of FeO2 by using density functional theory (DFT) and dynamic mean field theory (DMFT). The crystal structure of FeO2 is composed of Fe2+ and O2 2- dimers, where the Fe ions are surround by the octahedral O atoms. We found that the bond length of O2 dimer, which is very sensitive to the change of the Coulomb interaction U of Fe 3d orbital, plays an important role in determining the electronic structures. The band structures of DFT+DMFT show that the metal-insulator transition is driven by the change of U and pressure. We suggest that the correlation effect should be considered to correctly describe the physical properties of FeO2 compound.