An ab-initio approach to the optical properties of CxNy single wall nanotubes

We investigate the optical properties of (8,0) single wall carbon nanotubes (SWCNTs) alloyed with nitrogen (N) using relaxed carboncarbon (CC) bond length ab-initio density functional theory (DFT) calculations in the long wavelength limit. The Fermi energy of this doped system shows a unique maximum (7.52 eV) at 75% doping. This is in contrast with boron (B) doped system wherein a minimum is observed at the same doping concentration. It is observed that the magnitude of the static dielectric constant essentially depends on the nitrogen doping concentration as well as the direction of polarization. The static refractive index (real as well as imaginary) shows a unique maximum at 50% doping concentration in all three cases of electromagnetic field. All these factors may shed light on the nature of collective excitations in boron–carbon–nitrogen (B–C–N) nanotubules and other nanotube composite systems.