Stability of sp carbon (carbyne) chains

An sp carbon chain, which contains only one carbon atom in its cross section, is generally considered unstable. In this Letter, however, the DFT calculations showed that an isolated sp carbon chain is more stable than the smallest armchair (3,0)(3,0) and zigzag (2,2)(2,2) single-walled carbon nanotubes (SWCNT). This is consistent with the fact that an isolated sp carbon chain was observed by high-resolution transmission electron microscopy, but isolated (3,0)(3,0) and (2,2)(2,2) SWCNTs were never produced. Nevertheless, the sp chain is less stable than lager SWCNTs.