AB-INITIO STUDY OF THE GAP OPENING WITHIN THE GRAPHITE INTO DIAMOND TOPOLOGICAL TRANSFORMATION

In order to study the different types of interaction corresponding to either sp(2) or sp(3) carbon atoms, we investigate the changes in hybridization while continuously transforming rhombohedral graphite into cubic diamond. Using first-principles LMTO-ASA calculations, two different domains corresponding to semiconducting and semi-metallic phases are observed. A first-neighbour two-centre tight-binding Hamiltonian helped us to relate the opening of a band gap at the Fermi level to a competition between sigma and pi interactions. The influence of the sp coupling on the band-gap opening mechanisms is considered within the perturbation theory.