Wave packet propagation study of the charge transfer interaction in the F^- -Cu(111) and -Ag(111) systems

The electron transfer between an $F^{-}$ ion and $Cu(111)$ and $Ag(111)$ surfaces is studied by the wave packet propagation method in order to determine specifics of the charge transfer interaction between the negative ion and the metal surface due to the projected band gap. A new modeling of the $F^{-}$ ion is developed that allows one to take into account the six quasi-equivalent electrons of $F^{-}$ which are {\it a priori} active in the charge transfer process. The new model invokes methods of constrained quantum dynamics. The six-electron problem is transformed to two one-electron problems linked via a constraint. The projection method is used to develop a wave packet propagation subject to the modeling constraint. The characteristics (energy and width) of the ion $F^{-}$ ion level interacting with the two surfaces are determined and discussed in connection with the surface projected band gap.Comment: 34 pages, Revtex, 9 figures (postscript

Universal Dynamical Steps in the Exact Time-Dependent Exchange-Correlation Potential

We show that the exact exchange-correlation potential of time-dependent density-functional theory displays dynamical step structures that have a spatially non-local and time non-local dependence on the density. Using one-dimensional two-electron model systems, we illustrate these steps for a range of non-equilibrium dynamical situations relevant for modeling of photo-chemical/physical processes: field-free evolution of a non-stationary state, resonant local excitation, resonant complete charge-transfer, and evolution under an arbitrary field. Lack of these steps in usual approximations yield inaccurate dynamics, for example predicting faster dynamics and incomplete charge transfer

A push-pull unsymmetrical subphthalocyanine dimer

Unsymmetrical subphthalocyanine fused dimers have been prepared from appropriate ortho-dinitrile SubPc precursors. In particular, either electron-donating or electron-accepting substituents have been introduced on each SubPc constituent unit, resulting in unprecedented push–pull π-extended curved aromatic macrocycles. From fluorescence experiments in solvents of different polarity we conclude a dual fluorescence, namely a delocalized singlet excited state (1.73 eV) and a polarized charge transfer state (<1.7 eV). Pump probe experiments corroborate the dual nature of the fluorescence. On one hand, the delocalized singlet excited state gives rise to a several nanosecond lasting intersystem crossing yielding the corresponding triplet excited state. On the other hand, the polarized charge transfer state deactivates within a few picosesonds. Visualization of the charge transfer state was accomplished by means of molecular modeling with a slight polarization of the HOMO towards the electron donor and of the LUMO towards the electron acceptor

Modeling Single Electron Transfer in Si:P Double Quantum Dots

Solid-state systems such as P donors in Si have considerable potential for realization of scalable quantum computation. Recent experimental work in this area has focused on implanted Si:P double quantum dots (DQDs) that represent a preliminary step towards the realization of single donor charge-based qubits. This paper focuses on the techniques involved in analyzing the charge transfer within such DQD devices and understanding the impact of fabrication parameters on this process. We show that misalignment between the buried dots and surface gates affects the charge transfer behavior and identify some of the challenges posed by reducing the size of the metallic dot to the few donor regime.Comment: 11 pages, 7 figures, submitted to Nanotechnolog

Heat flow in InAs/InP heterostructure nanowires

The transfer of heat between electrons and phonons plays a key role for thermal management in future nanowire-based devices, but only a few experimental measurements of electron-phonon (e-ph) coupling in nanowires are available. Here, we combine experimental temperature measurements on an InAs/InP heterostructure nanowire system with finite element modeling (FEM) to extract information on heat flow mediated by e-ph coupling. We find that the electron and phonon temperatures in our system are highly coupled even at temperatures as low as 2 K. Additionally, we find evidence that the usual power-law temperature dependence of electron-phonon coupling may not correctly describe the coupling in nanowires and show that this result is consistent with previous research on similar one-dimensional electron systems. We also compare the strength of the observed e-ph coupling to a theoretical analysis of e-ph interaction in InAs nanowires, which predicts a significantly weaker coupling strength than observed experimentally.Comment: 9 pages, 6 figure

Hydrogen Balmer Line Broadening in Solar and Stellar Flares

The broadening of the hydrogen lines during flares is thought to result from increased charge (electron, proton) density in the flare chromosphere. However, disagreements between theory and modeling prescriptions have precluded an accurate diagnostic of the degree of ionization and compression resulting from flare heating in the chromosphere. To resolve this issue, we have incorporated the unified theory of electric pressure broadening of the hydrogen lines into the non-LTE radiative transfer code RH. This broadening prescription produces a much more realistic spectrum of the quiescent, A0 star Vega compared to the analytic approximations used as a damping parameter in the Voigt profiles. We test recent radiative-hydrodynamic (RHD) simulations of the atmospheric response to high nonthermal electron beam fluxes with the new broadening prescription and find that the Balmer lines are over-broadened at the densest times in the simulations. Adding many simultaneously heated and cooling model loops as a "multithread" model improves the agreement with the observations. We revisit the three-component phenomenological flare model of the YZ CMi Megaflare using recent and new RHD models. The evolution of the broadening, line flux ratios, and continuum flux ratios are well-reproduced by a multithread model with high-flux nonthermal electron beam heating, an extended decay phase model, and a "hot spot" atmosphere heated by an ultrarelativistic electron beam with reasonable filling factors: 0.1%, 1%, and 0.1% of the visible stellar hemisphere, respectively. The new modeling motivates future work to understand the origin of the extended gradual phase emission.Comment: 31 pages, 13 figures, 2 tables, accepted for publication in the Astrophysical Journa

Electron capture on iron group nuclei

We present Gamow-Teller strength distributions from shell model Monte Carlo studies of fp-shell nuclei that may play an important role in the pre-collapse evolution of supernovae. We then use these strength distributions to calculate the electron-capture cross sections and rates in the zero-momentum transfer limit. We also discuss the thermal behavior of the cross sections. We find large differences in these cross sections and rates when compared to the naive single-particle estimates. These differences need to be taken into account for improved modeling of the early stages of type II supernova evolution

Queuing models for abstracting interactions in Bacterial communities

Microbial communities play a significant role in bioremediation,plant growth,human and animal digestion,global elemental cycles including the carbon-cycle,and water treatment.They are also posed to be the engines of renewable energy via microbial fuel cells which can reverse the process of electrosynthesis.Microbial communication regulates many virulence mechanisms used by bacteria.Thus,it is of fundamental importance to understand interactions in microbial communities and to develop predictive tools that help control them,in order to aid the design of systems exploiting bacterial capabilities.This position paper explores how abstractions from communications,networking and information theory can play a role in understanding and modeling bacterial interactions.In particular,two forms of interactions in bacterial systems will be examined:electron transfer and quorum sensing.While the diffusion of chemical signals has been heavily studied,electron transfer occurring in living cells and its role in cell-cell interaction is less understood.Recent experimental observations open up new frontiers in the design of microbial systems based on electron transfer,which may coexist with the more well-known interaction strategies based on molecular diffusion.In quorum sensing,the concentration of certain signature chemical compounds emitted by the bacteria is used to estimate the bacterial population size,so as to activate collective behaviors.In this position paper,queuing models for electron transfer are summarized and adapted to provide new models for quorum sensing.These models are stochastic,and thus capture the inherent randomness exhibited by cell colonies in nature.It is shown that queuing models allow the characterization of the state of a single cell as a function of interactions with other cells and the environment,while being amenable to complexity reduction.Comment: IEEE Journal on Selected Areas in Communications (Bonus Issue on Emerging Technologies -- invited

Hydrodynamic simulations of metal ablation by femtosecond laser irradiation

Ablation of Cu and Al targets has been performed with 170 fs laser pulses in the intensity range of 10^12-10^14 W/cm^2. We compare the measured removal depth with 1D hydrodynamic simulations. The electron-ion temperature decoupling is taken into account using the standard "two-temperature model". The influence of the early heat transfer by electronic thermal conduction on hydrodynamic material expansion and mechanical behavior is investigated. A good agreement between experimental and numerical matter ablation rates shows the importance of including solid-to-vapor evolution of the metal in the current modeling of the laser matter interaction