Theoretical Studies of Structures and Electronic Properties of Single-Walled Carbon and Boron-Nitride Nanotubes

• Main Authors: Wen-Hao Chen, 陳文豪
• Other Authors: Bo-Cheng Wang
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/n9frau

博士 === 淡江大學 === 化學學系博士班 === 97 === The detailed geometrical structures of zigzag, armchair and chiral type single-walled carbon nanotubes (SWCNTs) and boron-nitride Nanotubes (SWBNTs) with infinite tubular length were investigated using localized Gaussian type orbital-periodic boundary condition-density functional theory (LGTO-PBC-DFT) method. It was found that the optimized structures of the zigzag, armchair type SWCNTs showed two C-C bond lengths that decrease with an increase in the tubular diameter. We found degeneracy in the highest occupied crystal orbitals if identical bond lengths were employed for the zigzag SWCNTs and the two-dimensional graphite sheet. This implies that the two different bond lengths found in the zigzag SWCNTs and the two-dimensional graphite sheet are probably due to the Jahn-Teller effect. The diameter decreasing and dwindling with the chiral angle of the chiral type single-walled carbon nanotubes cause the greatest structure to twist. The calculations of boron-nitride nanotubes reveal that the calculated Eg (band gap between HOCO and LUCO) increases with increasing tubular diameter and eventually converge to 5.03 eV for BN nanotubes of larger tubular diameter. According to the calculated Eg, the BN nanotubes are semiconductors and their conductivities are not sensitive to the tubular diameter. The calculated results also indicate that zigzag BN nanotubes with the tubular diameter larger than 18 Å display 3n properties in the calculated Eg, which is also obtained for zigzag carbon nanotubes.