We report the comparative study of electronic and optical properties of (6,1) SWCNT from GGA and DFT-1/2 methods. (6,1) SWCNT is a low-bandgap semiconductor, which falls within ( n1 − n2)/3≠ integer. The calculated bandgaps are 0.371 eV and 0.462 eV from GGA and DFT-1/2, respectively. Thus, DFT-1/2 enhanced the electronic bandgap by 24.52%. From both GGA and DFT-1/2 approaches (6,1) SWCNT exhibits an indirect bandgap along Γ − Δ symmetry. However, the percentage change in direct–indirect bandgap is negligibly small, i.e., 4.1% and 3.7% from GGA and DFT-1/2, respectively. The refractive index measured along x-axis ( n x ) approaches unity, indicating transparent behaviour, while that along z-axis ( n z ) goes as high as ∼3.82 for photon energy 0.0 − 0.15 eV, exhibiting opaque behaviour. Again, the value of n z drops below unity at photon energy ∼0.18 eV and again approaches ∼ 1 for higher energy ranges. The optical absorption is highly anisotropic and active within the infrared region.

    Abstract
    1 Introduction
    2 Computational details
    3 Results and discussion
        3.1 Electronic properties
        3.2 Optical properties
    4 Conclusion
    Acknowledgements 
    References

• D. P. Rai(Department of Physics, Physical Sciences Research Center)
• Y. T. Singh(Department of Physics, Physical Sciences Research Center (PSRC), Department of Physics, North-Eastern Hill University)
• B. Chettri(Department of Physics, Physical Sciences Research Center (PSRC), Department of Physics, North-Eastern Hill University)
• M. Houmad(Laboratory of Condensed Matter and Interdisciplinary Sciences (LaMScI), Faculty of Science, Mohammed V University of Rabat)
• P. K. Patra(Department of Physics, North-Eastern Hill University)