# LDA+DMFT approach to ordering phenomena and the structural stability of correlated materials

## TL;DR

This paper develops and applies a combined DFT+DMFT approach to study electronic and structural instabilities in correlated materials, revealing new phases and stability conditions driven by electron correlations.

## Contribution

It introduces a formalism for total energy and force calculations within charge self-consistent DFT+DMFT, enabling analysis of correlation-driven phase transitions and instabilities.

## Key findings

- Discovery of spinful exciton condensation in a two-orbital Hubbard model.
- Identification of correlation-induced structural instabilities in Fe and FeSe.
- Development of a computational scheme for total energies in DFT+DMFT.

## Abstract

Materials with correlated electrons often respond very strongly to external or internal influences, leading to instabilities and states of matter with broken symmetry. This behavior can be studied theoretically either by evaluating the linear response characteristics, or by simulating the ordered phases of the materials under investigation. We developed the necessary tools within the dynamical mean-field theory (DMFT) to search for electronic instabilities in materials close to spin-state crossovers and to analyze the properties of the corresponding ordered states. This investigation, motivated by the physics of LaCoO$_3$, led to a discovery of condensation of spinful excitons in the two-orbital Hubbard model with a surprisingly rich phase diagram. The results are reviewed in the first part of the article. Electronic correlations can also be the driving force behind structural transformations of materials. To be able to investigate correlation-induced phase instabilities we developed and implemented a formalism for the computation of total energies and forces within a fully charge self-consistent combination of density functional theory and DMFT. Applications of this scheme to the study of structural instabilities of selected correlated electron materials such as Fe and FeSe are reviewed in the second part of the paper.