We performed density-functional theory calculations in the local-density approximation of the structural, electronic, and optical properties of 4-Å-diameter single-walled carbon nanotubes. The calculated relaxed geometries show significant deviations from the ideal rolled graphene sheet configuration. We study the effect of the geometry on the electronic band structure finding the metallic character of the ͑5,0͒ nanotube to be a consequence of the high curvature of the nanotube wall. Calculations of the dielectric function and optical absorption of the isolated nanotubes were performed under light polarized parallel and perpendicular to the tube axis. We compare our results to measurements of the optical absorption of zeolite-grown nanotubes and are able to assign the observed maxima to the nanotube chiralities.

We show by ab initio calculations that the electron-phonon coupling matrix element M e-ph of the radial breathing mode in single-walled carbon nanotubes depends strongly on tube chirality. For nanotubes of the same diameter the coupling strength |M e-ph | 2 is up to one order of magnitude stronger for zig-zag than for armchair tubes. For (n1,n2) tubes M e-ph depends on the value of (n1 − n2) mod 3, which allows to discriminate semiconducting nanotubes with similar diameter by their Raman scattering intensity. We show measured resonance Raman profiles of the radial breathing mode which support our theoretical predictions.

The picotube molecule is a highly symmetric hydrocarbon, closely related to a very short ͑4,4͒ carbon nanotube. We present a thorough experimental and theoretical study of the physical properties of picotube crystals. In x-ray diffraction experiments we find the picotube molecules to display D 2d symmetry. We identify the most intense Raman peaks as A 1 modes with polarization-dependent Raman measurements. Ab initio calculations of the structural, electronic, and vibrational properties of picotubes are in excellent agreement with our experiments. We assign the measured vibrations to displacement eigenvectors including those analogous to the nanotube high-energy mode, the D mode, and the radial-breathing mode.

We investigated the influence of an epitaxially grown ZnS shell on the phonon spectra of CdSe nanorods of different sizes. The CdSe related Raman peaks shift with addition of a ZnS shell. The longitudinal optical phonon shifts slightly due to strain and the low‐energy shoulder shifts stronger, which can be explained within a model for surface optical phonons. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

We present ab initio calculations of electron-phonon coupling matrix elements of the totally symmetric high-energy vibrational modes of carbon nanotubes. The matrix elements depend on nanotube family ͑n 1 − n 2 ͒mod 3, chiral angle, and the particular optical transition, similarly to the radial-breathing mode. The strength of the matrix elements of the high-energy mode is up to 6 times higher than for the radial breathing mode. We discuss the implications of our results for the Raman spectrum of nanotubes and for charge carrier relaxation.