# Influence of Fock exchange in combined many-body perturbation and dynamical mean field theory

## TL;DR

This paper investigates how including the nonlocal Fock exchange term in combined many-body perturbation and dynamical mean field theory affects the phase diagram and interactions in electronic systems, revealing significant deviations from standard EDMFT especially in strong coupling.

## Contribution

It introduces the inclusion of the nonlocal Fock exchange term into EDMFT and $GW$+EDMFT, highlighting its impact on phase diagrams and interaction effects in correlated electronic systems.

## Key findings

- Nonlocal Fock exchange causes significant deviations in phase diagrams.
- Differences between EDMFT and $GW$+EDMFT are largest in strong-coupling regimes.
- $GW$+EDMFT results align closely with dual boson methods for moderate interactions.

## Abstract

In electronic systems with long-range Coulomb interaction, the nonlocal Fock exchange term has a band-widening effect. While this effect is included in combined many-body perturbation theory and dynamical mean field theory schemes, it is not taken into account in standard extended DMFT (EDMFT) calculations. Here, we include this instantaneous term in both approaches and investigate its effect on the phase diagram and dynamically screened interaction. We show that the largest deviations between previously presented EDMFT and $GW$+EDMFT results originate from the nonlocal Fock term, and that the quantitative differences are especially large in the strong-coupling limit. Furthermore, we show that the charge-ordering phase diagram obtained in $GW$+EDMFT methods for moderate interaction values is very similar to the one predicted by dual boson methods that include the fermion-boson or four-point vertex.