Extensive energy landscape sampling of nanotube end-caps reveals no chiral-angle bias for their nucleation

In the formation of a carbon nanotube (CNT) nucleus, a hemispherical fullerene end-cap, a specific pattern of six pentagons encodes what unique (n,m) chirality a nascent CNT would inherit, with many possible pentagon patterns corresponding to a single chirality. This configurational variety and its potential role in the initial stages of CNT catalytic growth remain essentially unexplored. Here we present large-scale calculations designed to evaluate the intrinsic energies of all possible CNT caps for selected chiralities corresponding to tube diameters d ≲ 1 nm. Our quantitative analysis reveals that for all chiral angles χ the energy scale variability associated with the CNT caps is small, compared to that of the CNT/catalyst interface. Such a flat energy landscape cannot therefore be a dominant factor for chiral distribution and lends further credibility to interface-controlled scenarios for selective growth of single-walled CNT of desired chirality.