Ab initiocalculations of exciton radiative lifetimes in bulk crystals, nanostructures, and molecules

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. arXiv:1901.08747v2 [cond-mat.mtrl-sci]

First-Principles Calculations of Exciton Radiative Lifetimes in Monolayer Graphitic Carbon Nitride Nanosheets: Implications for Photocatalysis

“…Converged spectra are computed within the static exchange approximation on denser 18 × 18 × 1 and 9 × 9 × 1 grids, using 150 and 300 bands for gC 3 N 4 -t and gC 3 N 4 -h, respectively, and a 2 Ry cutoff on the dielectric matrix for both materials. Once the BSE is solved, we compute the radiative lifetime, τ S , of each exciton state S at Q = 0 using Fermi's golden rule [50,51,90]. For Wannier excitons, the exciton dispersion in Q could be taken into account and the radiative lifetime renormalised by a thermal average on Q, assuming a parabolic dispersion.…”

Perturbo: A software package for ab initio electron–phonon interactions, charge transport and ultrafast dynamics

“…It can also simulate the ultrafast nonequilibrium electron dynam-ics in the presence of e-ph interactions. The developer branch, which is not publicly available yet, also includes routines for computing spin [8], electron-defect [9,10], and electron-photon interactions [11], as well as advanced methods to compute the ultrafast dynamics of electrons and phonons in the presence of electric and magnetic fields. These additional features will be made available in future releases.…”

Precise radiative lifetimes in bulk crystals from first principles: the case of wurtzite gallium nitride

“…Here, we extend our first-principles approach 14 to the case of a uniaxial bulk crystal, and use it to compute intrinsic radiative lifetimes in wurtzite GaN. The results agree well with experiment (within a factor of two) up to 100 K, and we include thermal exciton dissociation to retain quantitative accuracy up to room temperature.…”

“…We have recently shown a general first-principles approach that includes these physical features and can be applied broadly to systems ranging from isolated emitters to bulk crystals 14 . Its application to carbon nanotubes 15 , two-dimensional materials [16][17][18] , and recently gas phase molecules has shown results in very good agreement with experiments.…”

“…(7) reduces to the bulk isotropic case in Ref. 14 Finally, we take into account the fact that multiple exciton states can be occupied (including dark states with small transition dipoles, as is the case in GaN), and compute the radiative rate assuming a thermal equilibrium distribution:…”