Structural and electronic properties of N-doping ultra-small diameter (3,3) armchair SWCNT by using PBE and TB-mBJ potentials

The structural and electronic properties of (3,3) ultra-small SWCNT doped with nitrogen at different sites namely N(3, 3)_1, N(3, 3)_2 and N(3, 3)_3 are investigated by DFT method. The first model represents (3,3) small carbon-nitride nanotube (CNNT), the second and third models, three and two linear chains of N atoms replace a linear chain of C atoms in (3,3) SWCNT along the axis of nanotube. Our results show these last two models induce a strong structural deformation of the SWCNT by adopting a cross section in the form of a triangle-like and an ellipse-like respectively and all structures are energetically stable. The electronic properties (band structure, bandgap, total and partial density of states) were determined by using PBE and (TB-mBJ) potentials. After N-doping, the (3,3) SWCNT transforms from semiconductor to metal in CNNT. However, it keeps the same semiconductor behavior in the third model with increase in the bandgap. In N(3, 3)_2 model, the gap closes at two Weyl nodes which shows that this configuration is in Weyl semi-metal (WSM) state due to the break in symmetry. Furthermore, we observe that all DOS curves were changed a lot after doping and that the impurities levels appear clearly. Our results open new possibilities for developing electronic nanodevices of extremely small size and opens the field for experimental study of the new topological materials based on CNT doped with nitrogen.