Optical spectra of zigzag carbon nanotubes

Density functional theory was used to calculate optical properties of (4, 0) and (8, 0) zigzag carbon nanotubes. The optical spectra such as dielectric function, optical conductivity and optical absorption coefficient were simulated for the x and the z polarization of the incident photons. The results showed that the dielectric functions of these zigzag nanotubes are anisotropic. The joint density of states indicated that the 1D singularities at the JDOS of CNTs (8, 0) with z-polarization are higher than for CNTs (4, 0). For CNTs (8, 0) with z-polarization, around about 2.8 eV, optical conductivity is equal to 2100 Ω−1 cm−1 refer to high intra-band transition. Results show that by increasing the diameter of nanotubes the static optical refractive index and dielectric constant of zigzag CNTs increase.