Structural transformation of single wall carbon nanotube bundles under pressure

Structural transformation of single wall carbon nanotube bundles under hydrostatic pressure is studied by density functional theory (DFT) calculations. The results show that the transformation is related to the diameter and the symmetry of the nanotubes in a bundle. Due to the commensuration with the tetragonal symmetry, the (6,6), (8,8) and (10,10) bundles have two intermediate states in the process of the structural transformation, namely, the hexagonal and the tetragonal structures. In addition, the energy barrier for the structural transformation decreases in general with the increase of the diameter of the tubes, and is also influenced by the symmetry of the nanotubes. The DFT calculation of the nanotube bundles may provide useful insights into the mechanisms of the structural transformation and the potential applications of the nanotube bundles.