Maximally-localized Wannier Functions in Antiferromagnetic MnO within the FLAPW Formalism

TL;DR

This paper computes maximally-localized Wannier functions for antiferromagnetic MnO using the FLAPW method, revealing covalent interactions and orbital characteristics that elucidate magnetic ordering.

Contribution

It introduces a detailed calculation of Wannier functions in MnO within the FLAPW formalism, highlighting covalent bonding and orbital symmetry in antiferromagnetic MnO.

Findings

Identification of four trigonally-distorted sp^3-like Wannier functions for each oxygen.

Detection of weak covalent bonding between oxygen p states and manganese d states.

Characterization of manganese Wannier functions as crystal-field-modified atomic orbitals.

Abstract

We have calculated the maximally-localized Wannier functions of MnO in its antiferromagnetic (AFM) rhombohedral unit cell, which contains two formula units. Electron Bloch functions are obtained with the linearized augmented plane-wave method within both the LSD and the LSD+U schemes. The thirteen uppermost occupied spin-up bands correspond in a pure ionic scheme to the five Mn 3d orbitals at the Mn_1 (spin-up) site, and the four O 2s/2p orbitals at each of the O_1 and O_2 sites. Maximal localization identifies uniquely four Wannier functions for each O, which are trigonally-distorted sp^3-like orbitals. They display a weak covalent bonding between O 2s/2p states and minority-spin d states of Mn_2, which is absent in a fully ionic picture. This bonding is the fingerprint of the interaction responsible for the AFM ordering, and its strength depends on the one-electron scheme being used. The five Mn Wannier functions are centered on the Mn_1 site, and are atomic orbitals modified by the crystal field. They are not uniquely defined by the criterion of maximal localization and we choose them as the linear combinations which diagonalize the r^2 operator, so that they display the D_3d symmetry of the Mn_1 site.