Electronic structure studies of carbon based nanomaterials

This thesis deals with theoretical investigations of the electronic structure of conjugated carbon based materials. Novel materials like the C60 fullerene and the carbon nanotubes, but also the more well known, but closely related, graphite phase of carbon were studied. In addition, low dimensional structures like conjugated polymers and DNA, containing other atoms besides carbon, were investigated. The recently discovered fullerene phase of carbon, especially the C60 molecule has obtained a lot of attention among researchers. It has been observed that C60 under certain conditions can form linear polymeric chains, as well as two-dimensional polymeric structures. In the work presented in this thesis, Hückel model parameters have been developed for describing the intermolecular bonds within single bonded C60 polymers. These parameters were used in simulations to establish a simple rule explaining the phase diagram of the observed single bonded C6o polymer structures, namely that each electron added to a C60 monomer stimulates the creation of one single bond to a neighbouring C60 anion. A similar study on graphite was also performed, yielding Hückel parameters which describe the complicated bonding structure surrounding an atomic vacancy in the graphite. From calculations on large graphitic sheets containing several vacancies, insight was gained of the electronic properties associated with such defects, leading to a better understanding of Scanning Tunnelling Microscopy images of defected graphite. In one-dimensional materials, disorder is known to have an immense effect on electron localisation, seriously affecting the transport properties of these materials. Conjugated polymers and carbon nanotubes are not perfectly one-dimensional, but are often referred to as quasi one-dimensional. In this thesis, work is presented that deal with electron localisation in disordered quasi one-dimensional materials, studied at the Hückel level. To do this, a new method was developed