We determine the structure and energetics of the point defects in graphite from first principles calculations. The Jahn−Teller effect takes place at low temperature, breaking the symmetry and lowering the vacancy formation energy. This results in a weak in− plane reconstruction bond between two of the unsaturated atoms surrounding the vacancy and the displacement of the remaining unsaturated atom out of the plane. This last feature of the distortion increases the interaction of the vacancy with other defects, affecting its migration energy. We comment on the STM images of the symmetric and asymmetric vacancy and also the significance of these findings in understanding defect behaviour in irradiated graphite and related graphitic materials, in particular single walled nanotubes.

We present findings on the structure, energies and behaviour of defects in irradiated graphitic carbon materials. Defect production due to high-energy nuclear radiations experienced in graphite moderators is generally associated with undesirable changes in internal energy, microstructure and physical properties--the so-called Wigner effect. On the flip side, the controlled introduction and ability to handle such defects in the electron beam is considered a desirable way to engineer the properties of carbon nanostructures. In both cases, the atomic-level details of structure and interaction are only just beginning to be understood. Here, using a model system of crystalline graphite, we show from first-principles calculations, new details in the behaviour of vacancy and interstitial defects. We identify a prominent barrier-state to energy release, reveal a surprising ability of vacancy defects to bridge the widely spaced atomic layers, and discuss physical property and microstructure changes during irradiation, including interactions with dislocations.

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We study the interwall interaction and relative motion of walls in carbon nanotubes using density functional theory. The interwall interaction energy surface as a function of relative rotation and sliding of walls is calculated for the ͑5,5͒@͑10,10͒ nanotube. The barriers to relative rotation and sliding are estimated ab initio for the chiral walls of the ͑8,2͒@͑16,4͒ nanotube. These results are used to extract information on experimentally measurable quantities, such as threshold forces, diffusion coefficients, and mobilities of walls. Possible applications of these nanotubes in mechanical nanodevices are discussed. Two distinct regimes of the wall movement exist: athermal, forced movement ͑accelerating mode͒ and movement controlled by thermal diffusion ͑Fokker-Planck mode͒. We calculate the limits of these regimes from first principles.

We present a comparative spectroscopic study of carbon as graphite, diamond and C60 using C1s K-edge electron energy-loss spectroscopy (EELS), X-ray emission spectroscopy, and theoretical modelling. The first principles calculations of these spectra are obtained in the local density approximation using a self-consistent Gaussian basis pseudo-potential method. Calculated spectra show excellent agreement with experiment and are able to discriminate not only between various carbon hybridisations but also local variation in environment. Core-hole effects on the calculated spectra are also investigated. For the first time, the EEL spectrum of carbyne is calculated.