Steven Compernolle

Eigenstates and transmission coefficients of finite-sized carbon nanotubes

The tight-binding eigenstates of isolated finite-sized zigzag and armchair nanotubes are obtained analytically using the transfer matrix method. Edge states are encountered for zigzag tubes but not for armchair tubes. Inclusion of curvature leads to a decaying-oscillating behavior of the highest occupied and lowest unoccupied molecular orbital gap in armchair tubes as a function of length. For zigzag tubes the inclusion of curvature induces the conversion of an extended state at nonbonding energy to an edge state. In addition the transmission coefficient of zigzag and armchair tubes with featureless leads is analytically obtained. The existence of a transmission peak at the Fermi level that decays exponentially with nanotube length for zigzag tubes is explained.

Ab initio study of small graphitic cones with triangle, square, and pentagon apex

Accurate geometries of carbon nanocones of different sizes with a triangle, square or pentagon at the apex have been determined for the first time using a quantum chemical optimization method. The structure close to the apex is distorted from an ideal conical surface. The charging effect of the central defect is quite different from that predicted by tight-binding calculations. The symmetry behavior of the frontier orbitals and the size of the highest occupied molecular orbital-lowest unoccupied molecular orbital gap versus cone type and size is explained. The density of states quickly converges towards that of graphite when the size of the cone increases. In comparison to previous results in the literature it is found that the local densities of states of cones, that are locally different but belong to the same topo-combinatoric class, share common features.

Hiatus in the spherical shell model of fullerenes

The icosahedral multipoles that break the spherical symmetry in C20, C60 and C80 are identified as the L=6, 10, and 12 components respectively. In all these cages the dominant structural feature of the valence shell is the influence of the pentagonal defects.

A Simplified Quantum Mechanical Model for the Electron Distribution in a Si Nanowire

In order to investigate the technological potential ascribed to semiconductor nanowires, it is paramount to include quantum effects into the models used to simulate carrier trans-port as well as optical and excitonic features of various nanowire layouts.

Description of nanotubes using line group symmetry

In this work we relate the irreducible representations of the nanotubes to the zone-folding description of the first Brillouin zone. The complete set of symmetry elements for the armchair nanotube and their representations are given. Electronic π wavefunctions, with the appropriate symmetries are constructed and the irreducible representations, classified according to their symmetries, are assigned in the special points of the first Brillouin zone of an armchair nanotube.