Karsten Hannewald

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We have measured a strictly linear pi plasmon dispersion along the axis of individualized single-wall carbon nanotubes, which is completely different from plasmon dispersions of graphite or bundled single-wall carbon nanotubes. Comparative ab initio studies on graphene-based systems allow us to reproduce the different dispersions. This suggests that(More)
Electron doping turns semiconductors conductive even when they have wide fundamental band gaps. The degenerate electron gas in the lowest conduction-band states, e.g., of a transparent conducting oxide, drastically modifies the Coulomb interaction between the electrons and, hence, the optical properties close to the absorption edge. We describe these(More)
A large variety of gas phase conformations of the amino acids glycine, alanine, and cysteine is studied by numerically efficient semi-local gradient-corrected density functional theory calculations using a projector-augmented wave scheme and periodic boundary conditions. Equilibrium geometries, conformational energies, dipole moments, vibrational modes, and(More)
CONSPECTUS: Organic/inorganic hybrid structures are most exciting since one can expect new properties that are absent in either of their building blocks. They open new perspectives toward the design and tailoring of materials with desired features and functions. Prerequisite for real progress is, however, the in-depth understanding of what happens on the(More)
Based on a generalized theory of charge transport in organic crystals we investigate the motion of polarons of arbitrary size. Within this theory, we analyze the influence of characteristic electronic, vibronic, and thermal energies and their role for the transport regimes. The polaron bandwidth is identified as the central temperature-dependent quantity.(More)
Temperature-induced dynamic disorder is one of the great unknowns in charge transport through DNA and DNA-related systems. Using guanine crystals as a model system, we studied the temperature dependence and anisotropy of charge-carrier (hole) transport in guanine-based materials. Employing the Kubo formalism, we calculated the hole mobilities with ab initio(More)
A theory of time-resolved luminescence from photoexcited semiconductors is presented. It combines quantum kinetics of hot-carrier relaxation and quantum theory of spontaneous emission. Model calculations show the "transfer" of photoluminescence from the initial signal at the pump frequency via subsequent phonon replicas until the buildup of luminescence at(More)
We report first principles density functional theory studies on the basic ground state characteristics, dynamic properties, and the electronic structure of guanine crystals. The effect of water molecules within the crystal is studied in detail, and we discuss their influence on the structural, vibrational, and electronic properties. The geometries(More)