The presence of vacancy clusters in C nanotubes was assumed to explain the formation of C 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 6 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 the reconstruction of the nanotube atomic network. It was also demonstrated that there was a weak, but long-ranged, interaction between the vacancies; not only via strain fields but, due also to electronic effects - similar to those between 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 (5pp)