# Bandwidth renormalization due to the intersite Coulomb interaction

## TL;DR

This paper investigates how intersite Coulomb interactions influence correlated electron systems, focusing on screening and bandwidth renormalization, with applications to graphene and considerations of temperature effects.

## Contribution

It introduces a variational approach to distinguish screening from bandwidth renormalization effects and evaluates the Fock treatment's validity in correlated materials.

## Key findings

- Intersite interactions significantly affect bandwidth in graphene.
- Charge fluctuations are prominent at higher temperatures.
- The Fock treatment's applicability varies with system conditions.

## Abstract

The theory of correlated electrons is currently moving beyond the paradigmatic Hubbard $U$, towards the investigation of intersite Coulomb interactions. Recent investigations have revealed that these interactions are relevant for the quantitative description of realistic materials. Physically, intersite interactions are responsible for two rather different effects: screening and bandwidth renormalization. We use a variational principle to disentangle the roles of these two processes and study how appropriate the recently proposed Fock treatment of intersite interactions is in correlated systems. The magnitude of this effect in graphene is calculated based on cRPA values of the intersite interaction. We also observe that the most interesting charge fluctuation phenomena actually occur at elevated temperatures, substantially higher than studied in previous investigations.