Quasiparticle energies, excitonic effects and optical absorption spectra of small-diameter single-walled carbon nanotubes

We present a first-principles study of the effects of many-electron interactions on the optical properties of single-walled carbon nanotubes. Motivated by recent experiments, we have carried out ab initio calculations on the single-walled carbon nanotubes (3,3), (5,0) and (8,0). the calculations are based on a many-body Green's function approach in which both the quasiparticle (single-particle) excitation spectrum are determined. We show that the optical spectrum of both the semiconducting and metallic nanotubes studied exhibits important excitonic effects due to their quasi-one-dimensional nature. Binding energies for excitonic states range from zero for the metallic (5,0) tube to nearly 1 eV for the semiconducting (8,0) tube. Moreover, the metallic (3,3) tube possesses exciton states bound by nearly 100meV. Our calculated spectra explain quantitatively the observed features found in the measured spectra