Quantum chemical molecular dynamics were used to investigate the healing of single-walled carbon nanotubes during growth. In trajectories based upon self-consistent charge-density functional tight-binding energies and gradients, gas-phase carbon atoms were supplied to the carbon-iron boundary of a model C40Fe38 complex at two different rates (1C/0.5ps and 1C/10ps). The lower rate of carbon supply was observed to promote single-walled carbon nanotube growth, compared to the higher rate, for the same number of carbon atoms supplied. This promotion of growth was attributed to the suppression of pentagon and heptagon incorporation in the sp2 carbon network observed at lower carbon supply rates. The most successful example of growth occurred when the respective periods of hexagon and pentagon formation were out of phase and heptagon formation was limited. Higher carbon supply rates tended to result in the encapsulation of the Fe38 cluster by the extended sp2 carbon cap, due to a saturation of pentagon and heptagon defects in the latter. The greater tendency to hexagon formation, found using a lower carbon supply rate, was attributed to the relative rates of defect removal and addition from the sp2 carbon cap during growth. The defect removal (healing) process of the sp2 carbon cap occurred via ring isomerization, which resulted in the removal of 5-7, adatom, and monovacancy defects. These healing mechanisms generally occurred over time-scales of several picoseconds and depended largely upon the presence of the catalyst surface. The healing mechanisms observed here represented a possible pathway by which control over the (n,m) chirality of a nascent single-walled carbon nanotubes was obtained during the growth process.

Defect Healing During Single-Walled Carbon Nanotube Growth: a Density-Functional Tight-Binding Molecular Dynamics Investigation. A.J.Page, Y.Ohta, Y.Okamoto, S.Irle, K.Morokuma: Journal of Physical Chemistry C, 2009, 113[47], 20198-207