Excitons in two-dimensional atomic layer materials from time-dependent density functional theory

TL;DR

This paper demonstrates that time-dependent density functional theory (TDDFT) effectively predicts excitonic absorption spectra in 2D materials, capturing complex interlayer and intralayer excitons without heavy computational methods.

Contribution

The study shows that TDDFT with specific approximations accurately models excitonic effects in 2D materials, offering a computationally efficient alternative to MBPT methods.

Findings

TDDFT captures excitonic absorption peaks in 2D materials.

Layer stacking influences exciton character in bi-layer h-BN.

TDDFT successfully models spectra for monolayer TMDs like MoS₂ and MoSe₂.

Abstract

Time-dependent density functional theory (TDDFT) has been applied to the calculation of absorption spectra for two-dimensional atomic layer materials. We reveal that the character of the first bright exciton state of bi-layer hexagonal boron nitride (h-BN) is dependent on the layer stacking type through the use of many-body perturbation theory (MBPT) calculations, i.e., the electron and hole in the AA$'$ stacking are present in the same layer (intralayer exciton) while the A$'$B stacking exhibits an interlayer exciton. We demonstrate that the TDDFT approach with the meta-generalized gradient approximation to the exchange-correlation (XC) potential, and the Bootstrap XC kernel can capture the absorption peaks that correspond to these excitons without computationally heavy GW and Bethe-Salpeter equation calculations. We also show that the TDDFT method provides the absorption spectra for mono-layer transition metal dichalcogenides, MoS$_2$ and MoSe$_2$. This study confirms the validity of the TDDFT approach for the first investigation of the optical properties of complex two-dimensional atomic layer materials to which the MBPT calculation can not be readily applied.