Stone–Wales defect formation in the zigzag and armchair BC2N nanotubes: A DFT study

We have applied density functional calculations to investigate Stone Wales (SW) defect formation in three types of zigzag (4, 0) and two types of armchair (4, 4) BC2N nanotubes, with an extensive isomer search by considering various types of hexagon–hexagon bonds on the BC2N tube wall and two orientations of SW defect. According to our results, the isomers where SW defect is produced by the rotation of a C–C bond always are the most stable ones. Yielding smaller formation energy, the rotation of a C–C bond along the tube axis is easier than slanted ones. The rotation of each B–N bond about its center produces two different arrangements for SW defects in BC2N nanotubes, and those which avoid the unfavorable N–N and B–B bonds in the SW defects yield smaller values of defect formation energies in comparison to those of BN nanotubes. This indicates SW rearrangement process in the BC2N nanotubes is energetically more preferable in comparison to BNNTs. Since defects are inevitably formed during the growth of nanotubes, it is important to note that introduction of SW defect slightly modifies the density of states of BC2N nanotubes, i.e. band gaps are almost retained in the presence of SW defects.