We present quantum mechanical calculations using density functional theory and semiempirical methods, and molecular mechanics (MM) calculations with a Tersoff-Brenner potential that explore the role of vacancy defects in the fracture of carbon nanotubes under axial tension. These methods show reasonable agreement, although the MM scheme systematically underestimates fracture strengths. One- and two-atom vacancy defects are observed to reduce failure stresses by as much as ∼26% and markedly reduce failure strains. Large holes - such as might be introduced via oxidative purification processes - greatly reduce strength, and this provides an explanation for the extant theoretical-experimental discrepancies.
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We thank Andrew Rinzler for helpful discussions. We gratefully acknowledge the grant support from the NASA University Research, Engineering and Technology Institute on Bio Inspired Materials (BIMat) under award No. NCC-1-02037. R.S.R. appreciates additional support from the NSF Grant No. 0200797 (Ken Chong and Oscar Dillon, program managers) and the Office of Naval Research Grant (No. N000140210870).