# Ab Initio Calculations of Exciton Radiative Lifetimes in Bulk Crystals, Nanostructures and Molecules

## TL;DR

This paper introduces a comprehensive ab initio method to calculate exciton radiative lifetimes across various materials, including bulk crystals, nanostructures, and molecules, advancing the understanding of light emission from first principles.

## Contribution

The authors develop a unified first-principles approach to compute exciton radiative recombination rates in diverse material systems, extending previous methods focused mainly on absorption.

## Key findings

- Benchmark calculations for GaAs crystal show accurate lifetimes.
- Radiative lifetimes for gas-phase organic molecules are successfully computed.
- The method applies to bulk, nanostructured, and molecular materials.

## Abstract

Excitons are bound electron-hole pairs that dominate the optical response of semiconductors and insulators, especially in materials where the Coulomb interaction is weakly screened. Light absorption (including excitonic effects) has been studied extensively using first-principles calculations, but methods for computing radiative recombination and light emission are still being developed. Here we show a unified ab initio approach to compute exciton radiative recombination in materials ranging from bulk crystals to nanostructures and molecules. We derive the rate of exciton radiative recombination in bulk crystals, isolated systems, and in one- and two-dimensional materials, using Fermi's golden rule within the Bethe-Salpeter equation approach. We present benchmark calculations of radiative lifetimes in a GaAs crystal and in gas-phase organic molecules. Our work provides a general method for studying exciton recombination and light emission in bulk, nanostructured and molecular materials from first principles.