Strong effects of substitute nitrogen-doping on linear optical absorption spectra of zigzag carbon nanotubes

We theoretically study effects of substitute nitrogen-doping on linear optical properties of zigzag carbon nanotubes using tight-binding model and gradient approximation. It is found that, generally, nitrogen-doping reduces the value of absorption peaks and creates a number of new absorption peaks. In addition, near the low energy range, linear optical absorption spectra of nitrogen-doped (m,0) zigzag tubes are remarkably dependent on whether m mod 3 (the remainder of dividing m by 3) is equal to 0, 1 or 2.