Electron-hole pairs during the adsorption dynamics of O2 on Pd(100) - Exciting or not?

During the exothermic adsorption of molecules at solid surfaces dissipation of the released energy occurs via the excitation of electronic and phononic degrees of freedom. For metallic substrates the role of the nonadiabatic electronic excitation channel has been controversially discussed, as the absence of a band gap could favour an easy coupling to a manifold of electronhole pairs of arbitrarily low energies. We analyse this situation for the highly exothermic showcase system of molecular oxygen dissociating at Pd(100), using time-dependent perturbation theory applied to first-principles electronic-structure calculations. For a range of different trajectories of impinging O2 molecules we compute largely varying electron-hole pair spectra, which underlines the necessity to consider the high-dimensionality of the surface dynamical process when assessing the total energy loss into this dissipation channel. Despite the high Pd density of states at the Fermi level, the concomitant non-adiabatic energy losses nevertheless never exceed about 5% of the available chemisorption energy. While this supports an electronically adiabatic description of the predominant heat dissipation into the phononic system, we critically discuss the non-adiabatic excitations in the context of the O2 spin transition during the dissociation process.Comment: 20 pages including 7 figures; related publications can be found at http://www.fhi-berlin.mpg.de/th/th.html [added two references, changed V_{fsa} to V_{6D}, modified a few formulations in interpretation of spin asymmetry of eh-spectra, added missing equals sign in Eg.(2.10)

Computational design of metal-supported molecular switches: Transient ion formation during light- and electron-induced isomerisation of azobenzene

In molecular nanotechnology, a single molecule is envisioned to act as the basic building block of electronic devices. Such devices may be of special interest for organic photovoltaics, data storage, and smart materials. However, more often than not the molecular function is quenched upon contact with a conducting support. Trial-and-error-based decoupling strategies via molecular functionalisation and change of substrate have in many instances proven to yield unpredictable results. The adsorbate-substrate interactions that govern the function can be understood with the help of first-principles simulation. Employing dispersion-corrected Density-Functional Theory (DFT) and linear expansion Delta-Self-Consistent-Field DFT, the electronic structure of a prototypical surface-adsorbed functional molecule, namely azobenzene adsorbed to (111) single crystal facets of copper, silver and gold, is investigated and the main reasons for the loss or survival of the switching function upon adsorption are identified. The light-induced switching ability of a functionalised derivative of azobenzene on Au(111) and azobenzene on Ag(111) and Au(111) is assessed based on the excited-state potential energy landscapes of their transient molecular ions, which are believed to be the main intermediates of the experimentally observed isomerisation reaction. We provide a rationalisation of the experimentally observed function or lack thereof that connects to the underlying chemistry of the metal-surface interaction and provides insights into general design strategies for complex light-driven reactions at metal surfaces.Comment: 14 pages, 5 figures, submitted to J. Phys. Condens. Matte

Bistability loss as key feature in azobenzene (non-)switching on metal surfaces

Coinage metal adsorbed azobenzene is investigated as prototypical molecular switch. It is shown that switching capabilities are not just lost due to excited state quenching, but already due to changes in the ground state energetics. Electron demanding coadsorbates are suggested as strategy to regain the switching function.Comment: 8 pages, 3 figure

Assessing computationally efficient isomerization dynamics: Delta-SCF density-functional theory study of azobenzene molecular switching

We present a detailed comparison of the S0, S1 (n -> \pi*) and S2 (\pi -> \pi*) potential energy surfaces (PESs) of the prototypical molecular switch azobenzene as obtained by Delta-self-consistent-field (Delta-SCF) Density-Functional Theory (DFT), time-dependent DFT (TD-DFT) and approximate Coupled Cluster Singles and Doubles (RI-CC2). All three methods unanimously agree in terms of the PES topologies, which are furthermore fully consistent with existing experimental data concerning the photo-isomerization mechanism. In particular, sum-method corrected Delta-SCF and TD-DFT yield very similar results for S1 and S2, when based on the same ground-state exchange-correlation (xc) functional. While these techniques yield the correct PES topology already on the level of semi-local xc functionals, reliable absolute excitation energies as compared to RI-CC2 or experiment require an xc treatment on the level of long-range corrected hybrids. Nevertheless, particularly the robustness of Delta-SCF with respect to state crossings as well as its numerical efficiency suggest this approach as a promising route to dynamical studies of larger azobenzene-containing systems.Comment: 25 pages, 6 figure

NLO Simulations of Chargino Production at the ILC

We present an extension of the Monte Carlo Event Generator Whizard which includes chargino production at the ILC at NLO. We present two ways of adding photonic contributions. We present results for cross sections and event generation.Comment: 4 pages, to appear in Proceedings of SUSY06, the 14th International Conference on Supersymmetry and the Unification of Fundamental Interactions, UC Irvine, California, 12-17 June 200

Magnetic field dependence of hole levels in self-assembled InAs quantum dots

Recent magneto-transport experiments of holes in InGaAs quantum dots [D. Reuter, P. Kailuweit, A.D. Wieck, U. Zeitler, O. Wibbelhoff, C. Meier, A. Lorke, and J.C. Maan, Phys. Rev. Lett. 94, 026808 (2005)] are interpreted by employing a multi-band kp Hamiltonian, which considers the interaction between heavy hole and light hole subbands explicitely. No need of invoking an incomplete energy shell filling is required within this model. The crucial role we ascribe to the heavy hole-light hole interaction is further supported by one-band local-spin-density functional calculations, which show that Coulomb interactions do not induce any incomplete hole shell filling and therefore cannot account for the experimental magnetic field dispersion.Comment: 5 pages with 3 figures and one table. The paper has been submitted to Phys.Rev.