Diffusion quantum Monte Carlo andGWstudy of the electronic properties of monolayer and bulk hexagonal boron nitride

Abstract

We report diffusion quantum Monte Carlo (DMC) and many-body GW calculations of the electronic band gaps of monolayer and bulk hexagonal boron nitride (hBN). We find the monolayer band gap to be indirect. GW predicts much smaller quasiparticle gaps at both the single-shot G0W0 and the partially self-consistent GW0 levels. In contrast, solving the Bethe-Salpeter equation on top of the GW0 calculation yields an exciton binding energy for the direct exciton at the K point in close agreement with the DMC value. Vibrational renormalization of the electronic band gap is found to be significant in both the monolayer and the bulk. Taking vibrational effects into account, DMC overestimates the band gap of bulk hBN, while GW theory underestimates it.

Ellipsometry Study of Hexagonal Boron Nitride Using Synchrotron Radiation: Transparency Window in the Far‐UVC

“…This trend is in good agreement with recent DFT and quasiparticle calculations reported on monolayer and bulk h ‐BN. [ 52 ] The first excitonic peak at ≈6 eV (see Figure 1) is due to the transitions that are strongly renormalized by excitonic effects. In Figure 3, the electron–hole pair density of states that make up the excitonic transition at ≈6 eV is projected along the h ‐BN band structure and displayed as red shaded areas.…”

“…Such good agreement may be a consequence of a partial cancellation between effects of the vibrational renormalization of the bandgap and the underestimation of the quasiparticle bandgap by the GW calculations, both of which have been estimated to be around 200–400 meV. [ 52,53 ]…”

“…This trend is in good agreement with recent DFT and quasiparticle calculations reported on monolayer and bulk h-BN. [52] The first excitonic peak at %6 eV (see Figure 1) is due to the π ! π Ã transitions that are strongly renormalized by excitonic effects.…”

“…Such good agreement may be a consequence of a partial cancellation between effects of the vibrational renormalization of the bandgap and the underestimation of the quasiparticle bandgap by the GW calculations, both of which have been estimated to be around 200-400 meV. [52,53] Excitons in monolayer and few-layer h-BN have been analyzed in terms of Davydov multiplets, [54] revealing a structure in the imaginary part of the dielectric function that depends on the number of layers. A substantial increase in the direct bandgap and of the exciton binding energy was also reported in the monolayer owing to the reduction in screening.…”

Tuning the Direct and Indirect Excitonic Transitions of h-BN by Hydrostatic Pressure

“…The absorption peak is observed around ∼6.12 eV, in reasonable agreement with the values observed in Figure 1 a,b and coincident with previous ellipsometric measurements, 3 thus validating the approach used to extract excitonic transition energies from the reflectance data. Since the calculated electronic transitions are affected by the underestimation of the quasi-particle bandgap and the neglect of vibrational renormalization, 33 a small correction of ∼196 meV independent of pressure has been applied to the theoretical results to match the calculations with the experimental absorption peak at ambient pressure [magenta circle in Figure 6 a]. It is worth noting that the calculations predict a fairly constant direct exciton transition energy, whereas the experimental points show a small decrease with pressure.…”