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The radial dependency of the vibrational frequencies of single-wall carbon nanotubes in the G band (1500-1600 cm(-1)) is studied by density functional theory. In metallic nanotubes, a mode with A1 symmetry is found to be significantly softer than the corresponding mode in insulating tubes or graphite. The mechanism that leads to the mode softening is explored. It is reminiscent of the driving force inducing Peierls distortions. At ambient temperature, the energy gained by opening the gap is, however, not sufficient for a static lattice distortion. Instead the corresponding vibrational frequency is lowered.

The structure of the oxygen-induced p(4 x 4) reconstruction of Ag(111) is determined by a combination of scanning tunneling microscopy, surface x-ray diffraction, core level spectroscopy, and density functional theory. We demonstrate that all previous models of this surface structure are incorrect and propose a new model which is able to explain all our experimental findings but has no resemblance to bulk silver oxide. We also shed some light on the limitations of current density functional theories and the potential role of van der Waals interactions in the stabilization of oxygen-induced surface reconstructions of noble metals.

The thermodynamic equilibrium shape of rhodium and palladium crystals are predicted under conditions from ultrahigh vacuum to high oxygen pressures using the Gibbs-Wulff construction. The analysis is based on data obtained from ab initio calculations for the adsorption of oxygen on the low-index ͑111͒, ͑100͒, and ͑110͒ surfaces, and the stepped ͑311͒, ͑211͒, and ͑331͒ surfaces. While the close-packed ͑111͒ facets dominate the shape in the low-coverage cases, the higher adsorption energies at the more open surfaces lead to a rounding of the crystallite. A linear correlation between the surface energies of the clean surfaces and the respective adsorption energies is found.

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