Importance of pressure-dependent electronic interactions and magnetic order on pressure-driven insulator-metal transitions in MnO and NiO

TL;DR

This study investigates how pressure-dependent electronic interactions and magnetic order influence the insulator-metal transition in MnO and NiO, using advanced hybrid functional calculations to better match experimental observations.

Contribution

The paper introduces a pressure-dependent screening method within hybrid functionals to accurately model insulator-metal transitions in strongly correlated materials.

Findings

Hybrid functional with pressure-dependent screening accurately describes MnO transition.

NiO's insulating gap matches experimental trends and values better than fixed-parameter methods.

Magnetic order stability decreases under pressure as electronic interactions weaken.

Abstract

The pressure-driven insulator-metal transition is a crucial topic in condensed matter physics. However, even for the prototypical strongly correlated system, NiO, the critical pressure for transition remains debated. In this work, we evaluated the electronic interactions over a wide range of pressures based on our developed doubly-screened Coulomb correction method and investigated the effects of pressure-dependent electronic interactions and their interplay with magnetic order on the transition. As a validation of the method, we also performed calculations on MnO. The results show that the hybrid functional combined with pressure-dependent screening parameters reasonably describes the insulator-metal transition in MnO. The insulating band gap of antiferromagnetic (AFM) NiO also match well with experiments in both trend and value, which is better than the method using fixed parameters. Further calculations considering magnetic order indicate that as the electronic interactions weaken under pressure, the AFM state of NiO will no longer be stable, a phenomenon that was not observed in previous works. In addition, the results show that, compared with DFT+$U$ within the on-site Coulomb correction framework, the hybrid functional provides a more accurate description of the properties of MnO and NiO at high pressures, highlighting the key role of non-local effects. Our work provides a possible explanation for the long-standing discrepancies in NiO and offers guidance for the development of first-principles methods for correlated electron systems under pressure.