The IPsa of the SWCNTs were determined by applying the following procedures. The total energies of a neutral nanotube and a +1 charge radical cation (SWCNT radical dot+) of the same tube were calculated at the B3LYP/SVP level. The ionization energy was then obtained by subtracting the total energy of the neutral nanotube from the energy of the +1 charge nanotube radical cation