The presence of vacancy clusters in carbon nanotubes was assumed to explain the formation of carbon peapods and the difference between the experimentally measured and theoretical fracture strength of nanotubes. Atomistic simulations at various levels of theory were used to study the characteristics of large vacancies formed by up to six missing atoms. It was shown that the formation of big so-called holes on nanotube walls was energetically unfavorable, as the vacancies tended to split into smaller defects due to reconstruction of the nanotube atomic network. It was also demonstrated that there was a weak but long-range interaction between the vacancies; not only via strain fields but also due to electronic effects; similar to those of adatoms on metal surfaces.

Energetics, Structure, and Long-Range Interaction of Vacancy-Type Defects in Carbon Nanotubes: Atomistic Simulations. J.Kotakoski, A.V.Krasheninnikov, K.Nordlund: Physical Review B, 2006, 74[24], 245420