Band Gaps and Optical Spectra of Chlorographene, Fluorographene and Graphane from G₀W₀, GW₀ and GW Calculations on Top of PBE and HSE06 Orbitals

Abstract

The band structures of three graphene derivatives (chlorographene, fluorographene, and graphane) were analyzed at three levels of many-body GW theory (G0W0, GW0, and GW) constructed over GGA (PBE) and screened hybrid HSE06 orbitals. DFT band gap values obtained with the HSE06 functional were notably larger than those from PBE calculations but were significantly lower than band gaps from all GW calculations. On the other hand, all GW-type calculations gave similar band gaps despite some differences in band structures. The band gap (4.9 eV at the highest GW-HSE06 level) was predicted to be smaller than that of fluorographene (8.3 eV) or graphane (6.2 eV). However, chlorographene can be considered a wide-band gap insulator analogous to fluorographene and graphane. Using the Bethe-Salpeter equation, optical absorptions of graphene derivatives were found to be at significantly lower energies due to large binding energies of excitons (1.3, 1.9, and 1.5 eV for chlorographene, fluorographene, and graphane, respectively). Point defects lowered band gaps and absorption energies. Taking into account the low concentration of defects in this type of material, their effect on the discussed electronic properties was rather small.

Linear Scaling of the Exciton Binding Energy versus the Band Gap of Two-Dimensional Materials

“…3(b). The optical gap is 5.67 eV, consistent with the values of 5.4 eV ~ 5.6 eV from two previous GW-BSE studies [20,21]. These values are much higher than the lower limit of ~3.8 eV measured in a recent experiment [18], while a separate GW-BSE study reported almost the same optical gap as experimentally observed [22].…”

“…These values are much higher than the lower limit of ~3.8 eV measured in a recent experiment [18], while a separate GW-BSE study reported almost the same optical gap as experimentally observed [22]. As discussed previously [20,21,34], the discrepancy in the optical gap between theory and experiment could be ascribed to the [33]. In Fig.…”

Two‐Dimensional Fluorinated Graphene: Synthesis, Structures, Properties and Applications

“…As shown in Figure 9 , graphene had many notable peaks around 10–12 eV as a result of strong electron–hole correlations along with the appearance of bounded excitons in the ultraviolet region, opening the path toward an excitonic Bose‐Einstein condensate in graphene that was observed experimentally. [[qv: 12b]],56, 58 This feature was also obtained for fluorographene. A distinctive peak around 9.8 eV of fluorographene emerged in GW‐BSE that was evidently connected to strong electron‐hole coupling and was attributed to the transition from the near‐gap valence bands to the minimum conduction band.…”

Ultra high stiffness and thermal conductivity of graphene like C3N

“…According to our DFT results using the both functionals, the band-gap remains almost unchanged up to a high strain of 2/3ɛ uts . However, , we however emphasis that in the future studies more elaborated hybrid functionals such as GW [56][57][58][59][60] should be employed to discuss the electronic structure of C 3 N nanomembranes under different loading conditions. Thermal stability of a material at high temperatures is among the appealing properties for the practical applications.…”