Theoretical impacts of terminal atoms (C, B, N, and P) on fragments of single-walled hetero carbon nanotubes

Effects of terminal atoms on the energies and geometrical parameters of carbon nanotube (CNT) are reported. A fragment of (18,0) zigzag CNT (C108H36), with a length of two hexagonal structures, is compared and contrasted with its N-, (B-, N-), and P-substituted analogs: C72N36, C72N18B18, and C72P36, respectively, at AM1-RHF level. Terminating the CNT with P-atoms (C72P36) increases its relative conductivity and reactivity, through decreasing its band gap, and imposing conspicuous deformations on its edge honeycomb structures, puckering the P-atoms outward, and forming a wheel rim configuration. In contrast, no significant twist or deformation is observed on hexagonal rings of neither C72N36 nor C72N18B18. These CNTs appear with a cylindrical geometry and show relatively higher planarity and band gaps (ΔEHOMO-LUMO) than their unsubstituted C108H36 analog. Having C2 symmetry, CNT, N-CNT, and P-CNT appear practically nonpolar, whereas the asymmetric (B-, N-)CNT emerges with a dipole moment of 1.0 D.