Phonon softening in metallic nanotubes by a Peierls’ like mechanism

Density functional theory in the local approximation is used to study the radial dependency of the vibrational frequencies of single‐wall carbon nanotubes in the G band (1500–1600 cm−1) . In metallic nanotubes, the longitudinal A1 mode is found to be significantly softer than in insulating tubes or graphite. The mechanism that leads to the mode softening is reminiscent of the driving force inducing Peierls distortions, but the energy gained by opening the gap is not sufficient for a static lattice distortion. Instead, the corresponding vibrational frequency is lowered.