Crystal orbital study on carbon chains encapsulated in armchair carbon nanotubes with various diameters

Theoretical studies are presented on carbon nanowires (CNWs) made of linear carbon chains encapsulated inside armchair carbon nanotubes with various tube diameters. The structural and electronic properties as well as bonding features were investigated systematically by using ab initio self-consistent-field crystal orbital method based on density functional theory. The interaction between the tube and the chain becomes more obvious as the diameter of the CNW decreases and even weaker chemical bonds are formed between the tube and the chain in the smallest CNWs. The comparison of the elastic moduli between CNWs and CNTs supports that the mechanically unstable carbon chain is indeed protected by the CNT shell upon the encapsulation. All the CNWs we calculated are metals with zero band gaps. The encapsulation of the carbon chain may modulate the electronic properties for the CNWs depending on the tube size and the filling density of carbon atoms.