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F. Libisch:
"The electronic structure of graphene nanostructures";
Vortrag: Seminar Talk, University of Florida (eingeladen); 04.05.2015.

The special properties of graphene have created wide interest in
possible graphene-based nanoelectronic devices. A theoretical
understanding of the electronic structure of graphene in different
chemical environments, and ways to tailor them, are crucial for future
device applications. We investigate the electronic structure of
nanostructured graphene at different length scales, and different
levels of theory. For periacene atoms, small building blocks for
graphene nanodevices, high-level correlated wavefunction methods
(AQCC) reveal a high degree of radicality, as evident by fractional
occupations of many orbitals. For small graphene flakes (of the order
of a few nanometers) grown on iridium (111), we compare STM
measurements with DFT and tight-binding calculations and find good
agreement: at the flake edges, partially covalent bonding with the
metal surface leads to strong hybridization between the graphene bands
and the iridium surface state. Even larger quantum dot devices (of the
order of 50 nm in diameter) can be treated by tight-binding
approaches: we find that the edge roughness induced by the
lithographic pattering of the dots dominates their properties.

Graphene; Nanostructures; Tight Binding