Stability analysis of doped carbon nanotubes (CNTs)

It is well established that (3, 0), (3, 3), and (5, 0) carbon nanotubes (CNTs) are experimentally confirmed and are superconducting at low temperatures. In this study, the dynamical stability of (5, 0), (5, 5), and (7, 0) CNTs will be examined through phonon dispersion and ab initio molecular dynamics calculations as implemented in the QUANTUM ESPRESSO suite. Doping of the pristine CNTs with atoms of the groups IA, IIIA, IVA, and VA in the periodic table gives several stable structures but we show that the position of the doped atom in the primitive cell is crucial for the stability of the resulting structure. The bonding and vibration modes around the doped atoms are analyzed to elucidate the underlying cause of instability. The electron–phonon interaction and superconducting transition temperature (Tc) using McMillan–Allen–Dynes formula are also calculated for stable pristine and doped CNTs. We show that the Si doped (5,0) CNT exhibits superconductivity at Tc∼5.99 K.