  The phosphorus-doped single wall carbon nanotube (PSWCNT) is studied by using
First-Principle methods based on Density Function Theory (DFT). The formation
energy, total energy, band structure, geometry structure and density of states
are calculated. It is found that the formation energy of the P-doped single
carbon nanotubes increases with diameters; the total energy of carbon nanotubes
with the same diameter decreases as the doping rate increases. The effects of
impurity position on the im-purity level are discussed. It illustrates that the
position of the impurity level may depend on the C-P-C bond angle. According to
the above results, it is feasible to substitute a carbon atom with a phosphorus
atom in SWCNT. It is also found that P-doped carbon nanotubes are N type
semiconductor.
