Real-time ab initio simulations of excited carrier dynamics in carbon nanotubes

Combining time-dependent density functional calculations for electrons with molecular dynamics simulations for ions, we investigate the dynamics of excited carriers in a (3,3) carbon nanotube at different temperatures. Following an hν=6.8 eV photoexcitation, the carrier decay is initially dominated by efficient coupling to electronic degrees of freedom. At room temperature, the excitation gap is reduced to nearly half its initial value after ∼230 fs, where coupling to ionic motion starts dominating the decay. We show that the onset point and damping rate in the phonon regime change with initial ion velocities, a manifestation of temperature-dependent coupling between electronic and ionic degrees of freedom.
A. R. was supported by the EC projects NANOQUANTA (No. NMP4-CT-2004-500198), SANES (No. NMP4-CT-2006-017310), Spanish MCyT, and the Humboldt Foundation. D. T. was supported by NSF NIRT Grants No. DMR-0103587, No. ECS-0506309, NSF NSEC Grant No. EEC-425826, and the Humboldt Foundation.