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The quasiparticle band structure and optical properties of single-walledzigzag and armchair SiC nanotubes (SiC-NTs) as well as single SiC sheet areinvestigated by ab initio many-body calculations using the GW and the GW plusBethe-Salpeter equation (GW+BSE) approaches, respectively. Significant GWquasiparticle corrections of more than 1.0 eV to the Kohn-Sham band gaps fromthe local density approximation (LDA) calculations are found. The GWself-energy corrections transform the SiC sheet from a indirect LDA band gap toa direct band gap material. Furthermore, the quasiparticle band gaps of SiC-NTswith different chiralities behave very differently as a function of tubediameter, and this can be attributed to the difference in the curvature-inducedorbital rehybridization between the different chiral nanotubes. The calculatedoptical absorption spectra are dominated by discrete exciton peaks due toexciton states with large binding energy up to 2.0 eV in the SiC sheet andSiC-NTs. The formation of strongly bound excitons is attributed to the enhancedelectron-hole interaction in these low dimensional systems. Remarkably, theexcited electron amplitude of the exciton wavefunction is found to peak on theSi atoms near the hole position (which is on the C site) in the zigzag SiC-NTs,indicating a charge transfer from an anion (hole) to its neighboring cations byphotoexcitation. In contrast, this pronounced peak structure disappear in theexciton wavefunction in the armchair SiC-NTs. Furthermore, in the armchairSiC-NTs, the bound exciton wavefunctions are more localized and also stronglycylindrically asymmetric.

Excitonic effects in the optical properties of SiC sheet and nanotubes