[{"type":"speech","title":"Transport calculations for single molecules bases on density functional theory: some fundamentals","issued":{"date-parts":[["2005"]]},"author":[{"family":"Evers","given":"F."},{"family":"Burke","given":"K."},{"family":"Gaudoin","given":"R."}],"note":"Physik seit Albert Einstein : 69.Jahrestagung der DPG, Berlin, 4.-9.M\u00e4rz 2005 Verhandlungen der Deutschen Physikalischen Gesellschaft, R.6, B.40(2005) TT 33.13","abstract":"degrees of freedom. We distinguish between a coupling to the onsite energy of the molecule and a coupling representing a bond-stretching vibrational mode.\nThe full nonequilibrium current, shot noise, and dissipated power is calculated within the Keldysh Green function formalism. As far as transport\nobservables are concerned, onsite and bond-stretching coupling mechanisms di\ufb00er in several respects: In the latter case satellite peaks in the\ndi\ufb00erential conductance are more pronounced and results closer to the\nexperimental evidence can be obtained.\nTT 33.7 Di 15:30 TU H3027\nVibrational e\ufb00ects in transport through a few level molecule.\n\u2014 \u2022Dmitri Ryndyk \u2014 Universit\u00a8t Regensburg\nWe consider a simple molecule with several electron levels placed between large metallic leads. At \ufb01nite voltage internal vibrations of the\nmolecule as well as an oscillation of the whole molecule between the leads\ncan be excited. We use the self-consistent nonequilibrium theory to describe electron transport through a molecule and dynamics of vibrations.\nAt small voltage or high temperature current is a\ufb00ected by thermally\nexcited vibrations. At larger voltage and low enough temperature transition into the regime with nonequilibrium vibrations is possible. Phase\ndiagram of the system is controlled by coupling to the leads, electronvibron coupling, and coupling of vibrations to the thermal bath. The\nother nonequilibrium e\ufb00ect which should be taken into account is spectrum modi\ufb01cation due to nonequilibrium distribution function of electrons at \ufb01nite voltage.\nTT 33.8 Di 16:00 TU H3027\nTheoretical analysis of conductance histograms of Au atomic\ncontacts \u2014 \u2022F. Pauly1 , M. Dreher2 , J.C. Cuevas1 , E. Scheer2 ,\nversity of Karlsruhe, 76128 Karlsruhe, Germany \u2014 2 Physics Department,\nUniversity of Konstanz, 78457 Konstanz, Germany\nMany experiments have shown that the conductance histograms of\nmetallic atomic-sized contacts exhibit a peak structure, which is characteristic of the corresponding material. In order to shed some light on\nthe origin of these peaks, we present a theoretical analysis of the conductance histograms of Au atomic contacts, investigating the interplay\nbetween mechanical and electrical properties of these nanocontacts. We\nhave combined classical molecular dynamics simulations of the breaking\nof nanocontacts with conductance calculations based on a tight-binding\nmodel. This combination gives us access to crucial information such as\ncontact geometries, forces, minimum cross section, total conductance and\ntransmission coe\ufb03cients of the individual conduction channels. We also\ncompare with experimental results on Au atomic contacts where the individual channel transmissions have been determined.\nTT 33.9 Di 16:15 TU H3027\nUtilization of Carbon Nanotubes by Surface Acoustic Waves \u2014\n\u2022Jens Ebbecke1 , Christoph J. Strobl2 , and Achim Wixforth1\n\u2014 1 Institut f\u00a8r Physik der Universit\u00a8t Augsburg, Experimentalu\nphysik I, Universit\u00a8tsstr. 1, 86135 Augsburg \u2014 2 Sektion Physik der\nLudwig-Maximilian-Universit\u00a8t und Center for Nanoscience (CeNS),\nWe report a surface acoustic wave (SAW) mediated carbon nanotube\n(CNT) alignment parallel to the sample surface. The piezoelectric \ufb01eld\nof the SAW aligns the CNTs in parallel to the wave vector. Furthermore we have contacted single-walled CNTs after aligning them. The\nacoustoelectric current has been measured at 4.2 K and a probing of the\nlow-dimensional electronic states by the SAW has been detected. By decreasing the acoustic wavelength resulting in an adjustment to the length\nof the de\ufb01ned CNT constriction a quantization of the acoustoelectric current has been observed.\nTT 33.10 Di 16:30 TU H3027\nMagnetoconductance in Disordered Carbon-Nanotubes \u2014\n\u2022Norbert Nemec and G. Cuniberti \u2014 Molecular Computing\nGroup, Universit\u00a8t Regensburg, Germany\nSingle wall carbon-nanotubes in tight-binding approximation are one\nof the simplest nontrivial theoretical models with physical relevance that\ncan be used for studying quantum mechanical transport mechanisms at\nthe molecular scale. Based on this this model, we examine the interplay\nof disorder with external magnetic \ufb01elds, leading to signs of weak localization. As expected, weak localization is enhanced in the energy regions\nwith high density of states. We quantify the resulting energy dependent\nmean free path in relation to the sample size and the strength of the disorder. \u201cCoating wideband leads\u201d are introduced as a novel approach to\nmodel realistic contacts as they are found in experiment, without adding\nmuch computational complexity.\nTT 33.11 Di 16:45 TU H3027\nNon-linear transport properties in commensurate and incommensurate double-walled carbon nanotubes \u2014 \u2022Shidong Wang\nWe use a tight-binding model to investigate the e\ufb00ective intershell\ncoupling in double-walled carbon nanotubes. We derive an analytical\nexpression for the e\ufb00ective intershell coupling and \ufb01nd selection rules.\nThe intershell coupling between lowest bands is signi\ufb01cantly suppressed\nif two shells are incommensurate. Including the long-ranged Coulomb\ninteractions, double-walled carbon nanotubes can be described by Luttinger liquid theory at low energies. The tunneling density of states and\nthe non-linear I-V characteristics of double-walled carbon nanotubes are\nalso obtained.\nTT 33.12 Di 17:00 TU H3027\nFranck-Condon blockade and giant Fano factors in transport\nthrough single molecules \u2014 \u2022Jens Koch and Felix von Oppen\n14, 14195 Berlin\nWe show that Franck-Condon physics leads to a signi\ufb01cant current\nsuppression at low bias voltages (termed Franck-Condon blockade) in\ntransport through single molecules with strong coupling between electronic and vibrational degrees of freedom.\nFor weak vibrational relaxation, we \ufb01nd that transport in this regime\nis characterized by remarkably large Fano factors (102 \u2013103 ), which arise\ndue to avalanche-like transport of electrons. Avalanches occur in a selfsimilar manner over a wide range of time scales, as re\ufb02ected in power-law\ndependences of the current noise on frequency and vibrational relaxation\nrate.\nTT 33.13 Di 17:15 TU H3027\nTransport calculations for single molecules based on density\nfunctional theory: some fundamentals \u2014 \u2022F. Evers1 , K. Burke2 ,\nKarlsuhe, 76021 Karlsruhe, Germany \u2014 2 Department of Chemistry and\nChemical Biology, Rutgers University, 610 Taylor Road, Piscataway NJ\n08854\nIn principle, the use of time dependent density functional theory\n(TDDFT) allows for exact calculations of the linear and non-linear density and current response of interacting many-body systems. An important application of this method are transport calculations for single\nmolecules. In practice, one is forced to make approximations for the exchange correlation (XC) functional employed which then can put serious\nlimits to the accuracy of TDDFT calculations. We will discuss artifacts\nthat can occur if the non-equilibrium XC-functional is replaced by the\nequilibrium one. A formalism will be proposed that allows to include the\nXC-functional in the hydrodynamic approximation (Vignale and Kohn)\ninto the standard DFT-approach to transport.\nTT 33.14 Di 17:30 TU H3027\nElectron and Exciton Transfer in Donor-Acceptor Systems:\nMany-Particle E\ufb00ects and In\ufb02uence of Electronic Correlations\n\u2014 \u2022Sabine Tornow, Ning-Hua Tong, and Ralf Bulla \u2014 Theoretische Physik III, Institut f\u00a8r Physik, Universit\u00a8t Augsburg, 86135\nAugsburg, Germany\nThe spin boson model provides a well established description of electron transfer processes from a donor to an acceptor. The redox sites are\nmodelled by two localized quantum states. This picture breaks down in\nmulti electron transfer processes if many particle e\ufb00ects and electron\nco","kit-publication-id":"230060779"}]