Magnetic coupling constants for MnO as calculated using hybrid density functional theory

Andrew J Logsdail,Christopher A Downing,C Richard A Catlow,Alexey A Sokol

doi:10.1016/j.cplett.2017.10.027

Andrew J Logsdail, Christopher A Downing + Show 2 more

Open Access

https://doi.org/10.1016/j.cplett.2017.10.027

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Abstract

The properties of MnO have been calculated using generalised gradient approximation (GGA-) and hybrid (h-) density functional theory (DFT), specifically variants of the popular PBE and PBESol exchange–correlation functionals. The GGA approaches are shown to be poor at reproducing experimental magnetic coupling constants and rhombohedral structural distortions, with the PBESol functional performing worse than PBE. In contrast, h-DFT results are in reasonable agreement with experiment. Calculation of the Néel temperatures using the mean-field approximation gives overestimates relative to experiment, but the discrepancies are as low as 15 K for the PBE0 approach and, generally, the h-DFT results are significant improvements over previous theoretical studies. For the Curie–Weiss temperature, larger disparities are observed between the theoretical results and previous experimental results.

Highlights

Transition metal oxides (TMOs) are popular materials for studying fundamental physical properties because of their relative structural simplicity and intriguing magnetic behaviour, where a transition from paramagnetic to antiferromagnetic (AFM) ordering occurs below their respective Néel temperature (TN) [1]
MnO is a classic representation of the family of first row TMOs: at room temperature, it is paramagnetic (PM) and adopts a cubic structure with a lattice constant (a) of 2.223 Å [2,3,4]; short-range magnetic ordering occurs below the Curie–Weiss temperature (h) of $ 550 K [5] and below the TN of 118 K [6], MnO adopts a longrange ordered AFM spin configuration [7]
At the local and semi-local level of density functional theory (DFT), such as the local density approximation (LDA) and generalised gradient approximation (GGA), problems exist due to the inadequacy of the exchange–correlation (XC) functionals at localising the valence d electrons [15,16,17], partly due to inherent selfinteraction errors [18,19,20], which leads to underestimation of the electronic band gap

Summary

Introduction

Transition metal oxides (TMOs) are popular materials for studying fundamental physical properties because of their relative structural simplicity and intriguing magnetic behaviour, where a transition from paramagnetic to antiferromagnetic (AFM) ordering occurs below their respective Néel temperature (TN) [1]. Insight into the fundamental properties of TMOs, such as spin configuration and associated coupling constants, is aided by computational simulations; MnO has a long-standing reputation of being a challenge to simulate using modern density functional theory (DFT) due to strong on-site Coulomb repulsion by the 3d states [12,13,14]. To compare systematically different levels of DFT theory when studying the properties of MnO, one can consider the energetics of the several competing low-temperature magnetic configurations: the relative energy differences between spin configurations can be used to derive observables such as TN and h. We build on previous computational investigations by calculating and comparing the magnetic coupling constants and transition temperatures for MnO using several popular exchange– correlation (XC) density functionals of similar theoretical origins, considering a recent reparameterisation for solidstate materials and contrasting this to the original derivation made using free atom assumptions.

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