# Symmetry-Breaking Polymorphous Descriptions for Complex Materials without Interelectronic U

## TL;DR

This paper demonstrates that mean-field density-functional theory with polymorphous representations can accurately predict electronic properties of correlated complex materials without requiring the interelectronic U, challenging traditional Mott insulator models.

## Contribution

The study introduces a polymorphous DFT approach that lifts degeneracies and opens band gaps in correlated materials without the need for an explicit interelectronic U term.

## Key findings

- Successfully predicts magnetic moments and band gaps for MnO, FeO, CoO, NiO
- Shows polymorphous DFT can differentiate magnetic phases
- Offers an alternative to Mott-Hubbard models for complex materials

## Abstract

Correlated materials with open-shell d- and f-ions having degenerate band edge states show a rich variety of interesting properties ranging from metal-insulator transition to unconventional superconductivity. The textbook view for the electronic structure of these materials is that mean-field approaches are inappropriate, as the interelectronic interaction U is required to open a band gap between the occupied and unoccupied degenerate states while retaining symmetry. We show that the latter scenario often defining what Mott insulators are, is in fact not needed for the 3d binary oxides MnO, FeO, CoO, and NiO. The mean-field band theory can indeed lift such degeneracies in the binaries when nontrivial unit cell representations (polymorphous networks) are allowed to break symmetries, in conjunction with a recently developed non-empirical exchange and correlation density-functional without an on-site interelectronic interaction U. We explain how density-functional theory (DFT) in the polymorphous representation achieves band gap opening in correlated materials through a separate mechanism to the Mott-Hubbard approach. We show the method predicts magnetic moments and gaps for the four binary monoxides in both the antiferromagnetic and paramagnetic phases, offering an effective alternative to symmetry-conserving approaches for studying a range of functionalities in open d- and f-shell complex materials.

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Source: https://tomesphere.com/paper/1906.06467