# Structural and electronic properties of $\alpha,\beta$-(BEDT-TTF)$_2$I$_3$ and $\kappa$-(BEDT-TTF)$_2$X$_3$ (X=I,F,Br,Cl) organic charge transfer salts

## TL;DR

This study uses advanced ab initio calculations to explore the structural and electronic properties of various BEDT-TTF-based charge transfer salts, revealing topologically protected band crossings and effects of halogen substitution.

## Contribution

It provides detailed ab initio analysis of multiple phases of BEDT-TTF salts, including symmetry, band crossings, and effects of halogen substitution, which are novel insights into their electronic structure.

## Key findings

- Identification of topologically protected band crossings in F-substituted salt
- Analysis of symmetry and irreducible representations of electronic bands
- Effect of halogen substitution on electronic properties and strain

## Abstract

(BEDT-TFF)$_2$I$_3$ charge transfer salts are reported to show superconductivity and pressure induced quasi two-dimensional Dirac cones at the Fermi level. By performing state of the art ab initio calculations in the framework of density functional theory, we investigate the structural and electronic properties of the three structural phases $\alpha$, $\beta$ and $\kappa$. \edit{We furthermore report about the irreducible representations of the corresponding electronic band structures, symmetry of their crystal structure, and discuss the origin of band crossings. Additionally, we discuss the chemically induced strain in $\kappa$-(BEDT-TTF)$_2$I$_3$ achieved by replacing the Iodine layer with other Halogens: Fluorine, Bromine and Chlorine. In the case of $\kappa$-(BEDT-TTF)$_2$F$_3$, we identify topologically protected crossings within the band structure. These crossings are forced to occur due to the non-symmorphic nature of the crystal.} The calculated electronic structures presented here are added to the organic materials database (OMDB).