# Discovering new two-dimensional topological insulators from computational screening

## TL;DR

This study computationally screened 3331 2D materials to identify new topological insulators, revealing 46 quantum spin Hall, 7 quantum anomalous Hall, and 9 crystalline topological insulators, with detailed analysis on their stability and electronic properties.

## Contribution

Introduced a comprehensive b initio scheme to identify topological phases in 2D materials from a large database, discovering several novel topological insulators.

## Key findings

- Identified 46 quantum spin Hall insulators, 7 quantum anomalous Hall insulators, and 9 crystalline topological insulators.
- Found that topological indices are highly sensitive to exchange-correlation functional approximations.
- Calculated a 0.65 eV gap for PdSe, larger than known 2D topological insulators.

## Abstract

We have performed a computational screening of topological two-dimensional (2D) materials from the Computational 2D Materials Database (C2DB) employing density functional theory. A full \textit{ab initio} scheme for calculating hybrid Wannier functions directly from the Kohn-Sham orbitals has been implemented and the method was used to extract $\mathbb{Z}_2$ indices, Chern numbers and Mirror Chern numbers of 3331 2D systems including both experimentally known and hypothetical 2D materials. We have found a total of 46 quantum spin Hall insulators, 7 quantum anomalous Hall insulators and 9 crystalline topological insulators that are all predicted to be dynamically stable. Roughly one third of these were known prior to the screening. The most interesting of the novel topological insulators are investigated in more detail. We show that the calculated topological indices of the quantum anomalous Hall insulators are highly sensitive to the approximation used for the exchange-correlation functional and reliable predictions of the topological properties of these materials thus require methods beyond density functional theory. We also performed $GW$ calculations, which yield a gap of 0.65 eV for the quantum spin Hall insulator PdSe$_2$ in the MoS$_2$ crystal structure. This is significantly higher than any known 2D topological insulator and three times larger than the Kohn-Sham gap.