Carbon nanotube fracture - Differences between quantum mechanical mechanisms and those of empirical potentials

We present quantum mechanical (QM) studies of carbon nanotube (CNT) fracture using two different semiempirical methods. One proposed mechanism for CNT fracture - based mainly on studies with empirical potentials - involves an aggregation of Stone-Wales defects followed by a ring-opening step whereby a bond between two 5-membered rings is severed. We have performed QM studies which instead predict that this bond is a particularly strong one, and that the failing bonds lie within the pentagons. We also explore why empirical bond-order potentials (in particular, a potential of Brenner and coworkers) predict qualitatively different fracture mechanisms than quantum mechanical calculations do.