First principal study on optical properties of carbon and gallium nitride nanotubes

In this work, we study electronic and optical properties of two (5,5) armchair carbon nanotube (CNT) and gallium nitride nanotube (GaNNT) using fully self-consistence density functional theory (DFT) based calculations as implemented in SIESTA package. The generalized gradient approximation (GGA) is considered for the exchange-correlation functional. The results show that the armchair CNT is a metal, whereas the armchair GaNNT is a semiconductor with an indirect band gap. We can find the optical properties strongly depending on direction of polarization of light, hence the dielectric function and the optical absorption spectra are different for light polarized parallel and perpendicular to tubes axis. The significant peaks in the considered parameters are related to the ultraviolet to infrared (UV-IR) spectral region, and their intensities depend on the tubular morphology of the tubes. Our results can serve as a base for developments in designing nano-electronic and nano-optoelectronics devices.