Carbon nanotubes with periodic vacancy defects to phenine nanotubes: A DFT study

In the present paper a systematic investigation has been performed to study the structural and electronic properties of phenine nanotubes (pNT(n,n)) within framework of density functional theory. pNT (n,n) molecules with n = 3–15 have been obtained by introducing periodic 6 atom vacancy defects periodically in pristine carbon nanotubes. Our results have shown that symmetric pNT(n,n) structures can only be formed with n = 3, 6, 9, 12 and 15. For other values of n, non-symmetric hybrid pNT(n,n) structures were obtained. The symmetric pNT(n,n) molecules have exhibited perfectly ordered structures, with a periodic vacancy and large voids up to 63% of the molecule. The bond filling index and atom filling index of all symmetric pNT(n,n) molecules was found to be 63%and 57% respectively. The binding energy calculation have shown that pNT(n,n) structures are quite stable, however they are slightly less stable in comparison to non-symmetric pNT(n,n). All pNT(n,n) molecules have been found to be semiconducting in nature with wide HOMO-LUMO energy gap with HOMO-LUMO gap of pNT(n,n) in the range of 1.58 eV–2.98 eV. The HOMO-LUMO gap varies in an oscillatory manner with increase in the size of pNT(n,n) molecules with maximum values for symmetric structures. The results are in agreement with the available experimental results. The pNT(n,n) molecules with large stability, huge voids and tunable electronic properties offers many interesting applications in optoelectronic devices.