Tamar Seideman

Northwestern University, Evanston, Illinois, United States

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Publications (218)881.66 Total impact

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    ABSTRACT: Shaped ultrafast laser pulses were used to study and control the ionization dynamics of electronically excited pyrazine in a pump and probe experiment. For pump pulses created without feedback from the product signal, the ion growth curve (the parent ion signal as a function of pump/probe delay) was described quantitatively by the classical rate equations for internal conversion of the $S_2$ and $S_1$ states. Very different, non-classical behavior was observed when a genetic algorithm (GA) was used to minimize the ion signal at some pre-determined target time, T. Two qualitatively different control mechanisms were identified for early (T$<1.5$ ps) and late (T$>1.5$ ps) target times. In the former case, the ion signal was largely suppressed for $t<T$, while for $t \gg T$ the ion signal produced by the GA-optimized pulse and a transform limited (TL) pulse coalesced. In contrast, for $T>1.5$ ps the ion growth curve followed the classical rate equations for $t<T$, while for $t \gg T$ the quantum yield for the GA-optimized pulse was much smaller than for a TL pulse. We interpret the first type of behavior as an indication that the wave packet produced by the pump laser is localized in a region of the $S_2$ potential energy surface where the vertical ionization energy exceeds the probe photon energy, whereas the second type of behavior may be described by a reduced absorption cross section for $S_0 \rightarrow S_2$ followed by incoherent decay of the excited molecules.
    09/2014;
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    ABSTRACT: We suggest the combination of single molecule pulling and optical control as a way to enhance control over the electron transport characteristics of a molecular junction. We demonstrate using a model junction consisting of biphenyl-dithiol coupled to gold contacts. The junction is pulled while optically manipulating the dihedral angle between the two rings. Quantum dynamics simulations show that molecular pulling enhances the degree of control over the dihedral angle and hence over the transport properties.
    Nano letters. 07/2014;
  • Joshua E Szekely, Tamar Seideman
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    ABSTRACT: Although the vast majority of studies of transport via molecular-scale heterojunctions have been conducted in the (static) energy domain, experiments are currently beginning to apply time domain approaches to the nanoscale transport problem, combining spatial with temporal resolution. It is thus an opportune time for theory to develop models to explore both new phenomena in, and new potential applications of, time-domain, coherently driven molecular electronics. In this work, we study the interaction of a molecular phonon with an electronic wavepacket transmitted via a conductance junction within a time-domain model that treats the electron and phonon on equal footing and spans the weak to strong electron-phonon coupling strengths. We explore interference between two coherent energy pathways in the electronic subspace, thus complementing previous studies of coherent phenomena in conduction junctions, where the stationary framework was used to study interference between spatial pathways. Our model provides new insights into phase decoherence and population relaxation within the electronic subspace, which have been conventionally treated by density matrix approaches that often rely on phenomenological parameters. Although the specific case of a transport junction is explored, our results are general, applying also to other instances of coupled electron-phonon systems.
    The Journal of chemical physics. 07/2014; 141(4):044103.
  • Alexei Deinega, Tamar Seideman
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    ABSTRACT: We explore the interaction between a quantum emitter and a metal nanoring by numerical solution of coupled Maxwell-Liouville equations. When the quantum emitter and nanoring are subjected to an incident plane wave, coupling between the quantum emitter and a dark plasmon supported by the nanoring gives rise to a similar lineshape to the familiar Fano type. It results from the excitation of a dark plasmon via intermediary participation of the quantum emitter. The dark plasmon is characterized through the width and shift parameters of the emitter peak in the absorption spectrum of the nanoparticle. Our results are obtained with the help of finite-difference time-domain method and a recently proposed symmetry-adapted averaging approach.
    The Journal of Chemical Physics 06/2014; 140(23):234311. · 3.12 Impact Factor
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    ABSTRACT: We present an approach to accurately construct the few-state model Hamiltonians for singlet fission processes on the basis of an ab initio electronic structure method tailored to dimer wave functions, called an active space decomposition strategy. In this method, the electronic structure of molecular dimers is expressed in terms of a linear combination of products of monomer states. We apply this method to tetracene and pentacene, using monomer wave functions computed by the restricted active space (RAS) method. Near-exact wave functions are computed for π-electrons of dimers that contain up to 7 × 1012 electronic configurations. Our product ansatz preserves the diabatic picture of the minimal dimer model, allowing us to accurately identify model Hamiltonians. The wave functions obtained from the model Hamiltonians account for more than 99% of the total wave functions. The resulting model Hamiltonians are shown to be converged with respect to all the parameters in the model, and corroborate previously reported coupling strengths.
    The Journal of Physical Chemistry C 06/2014; 118(24):12700–12705. · 4.84 Impact Factor
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    ABSTRACT: This paper describes analytical and numerical results from a model Hamiltonian method applied to electron transfer (ET) from a quasicontinuum (QC) of states to a set of discrete states, with and without a mediating bridge. Analysis of the factors that determine ET dynamics yields guidelines for achieving high-yield electron transfer in these systems, desired for instance for applications in heterogeneous catalysis. These include the choice of parameters of the laser pulse that excites the initial state into a continuum electronic wavepacket and the design of the coupling between the bridge molecule and the donor and acceptor. The vibrational mode on a bridging molecule between donor and acceptor has an influence on the yield of electron transfer via Franck-Condon factors, even in cases where excited vibrational states are only transiently populated. Laser-induced coherence of the initial state as well as energetic overlap is crucial in determining the ET yield from a QC to a discrete state, whereas the ET time is influenced by competing factors from the coupling strength and the coherence properties of the electronic wavepacket.
    The Journal of Chemical Physics 04/2014; 140(14):144102. · 3.12 Impact Factor
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    ABSTRACT: Tip-enhanced Raman Spectroscopy (TERS) provides chemical information for adsorbates with nanoscale spatial resolution, single-molecule sensitivity, and, when combined with scanning tunneling microscopy (STM), Ångstrom-scale topographic resolution. Performing TERS under ultrahigh vacuum (UHV) conditions allows pristine and atomically smooth surfaces to be maintained, while liquid He cooling minimizes surface diffusion of adsorbates across the solid surface, allowing direct STM imaging. Low temperature (LT)-TER spectra differ from room temperature (RT)-TER, RT-surface-enhanced Raman (SER), and LT-SER spectra because the vibrational lines are narrowed and shifted, revealing additional chemical information about adsorbate-substrate interactions. As an example, we present LT-TERS for the Rhodamine 6G (R6G)/Ag(111) system that exhibits such unique spectral shifts. The high spectral resolution of LT-TERS provides intramolecular insight in that the shifted modes are associated with the ethylamine moiety of R6G. LT-TERS is a promising approach for unraveling the intricacies of adsorbate-substrate interactions that are inaccessible by other means.
    Journal of the American Chemical Society 02/2014; · 10.68 Impact Factor
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    ABSTRACT: High-order harmonic generation in an atomic or molecular gas is a promising source of sub-femtosecond vacuum ultraviolet coherent radiation for transient scattering, absorption, metrology and imaging applications. High harmonic spectra are sensitive to Ångstrom-scale structure and motion of laser-driven molecules, but interference from radiation produced by random molecular orientations obscures this in all but the simplest cases, such as linear molecules. Here we show how to extract full body-frame high harmonic generation information for molecules with more complicated geometries by utilizing the methods of coherent transient rotational spectroscopy. To demonstrate this approach, we obtain the relative strength of harmonic emission along the three principal axes in the asymmetric-top sulphur dioxide. This greatly simplifies the analysis task of high harmonic spectroscopy and extends its usefulness to more complex molecules.
    Nature Communications 02/2014; 5:3190. · 10.74 Impact Factor
  • Alexei Deinega, Tamar Seideman
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    ABSTRACT: We propose two complementary approaches for solution of the coupled Maxwell-Liouville equations within the finite-difference time domain (FDTD) framework. The two methods are specifically designed to eliminate self-interaction, which often appears spuriously in simulation of the coupled Maxwell-Liouville equations, and hence can be used for modeling of single as well as ensembles of quantum emitters (such as molecules or quantum dots) in an arbitrary dielectric environment. One approach borrows from the familiar total field-scattered field technique that has been applied in the past in a different context. The second recognizes an opportunity to average over the electric field at a set of specifically chosen points around the quantum emitter. The methods introduced are applied to two problems of growing current interest that also present useful test cases. One is the modeling of spontaneous emission, where comparison with an analytical solution illustrates the accuracy and efficiency of the methodology. The second is quantum-emitter-induced transparency in a resonator formed by two gold ellipsoids, where Fano interferences suggest interesting potential applications.
    01/2014; 89(2).
  • Zixuan Hu, Tamar Seideman, Mark A. Ratner
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    ABSTRACT: We develop a numerical approach for simulating light-induced charge transport dynamics across a metal-molecule-metal conductance junction. The finite-difference time-domain method is used to simulate the plasmonic response of the metal structures. The Huygens subgridding technique, as adapted to Lorentz media, is used to bridge the vastly disparate length scales of the plasmonic metal electrodes and the molecular system, maintaining accuracy. The charge and current densities calculated with classical electrodynamics are transformed to an electronic wavefunction, which is then propagated through the molecular linker via the Heisenberg equations of motion. We focus mainly on development of the theory and exemplify our approach by a numerical illustration of a simple system consisting of two silver cylinders bridged by a three-site molecular linker. The electronic subsystem exhibits fascinating light driven dynamics, wherein the charge density oscillates at the driving optical frequency, exhibiting also the natural system timescales, and a resonance phenomenon leads to strong conductance enhancement.
    The Journal of Chemical Physics 01/2014; 141:224104. · 3.12 Impact Factor
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    ABSTRACT: We present a real-space method for first-principles nano-scale electronic transport calculations. We use the non-equilibrium Green's function method with density functional theory and implement absorbing boundary conditions (ABCs, also known as complex absorbing potentials, or CAPs) to represent the effects of the semi-infinite leads. In real space, the Kohn-Sham Hamiltonian matrix is highly sparse. As a result, the transport problem parallelizes naturally and can scale favorably with system size, enabling the computation of conductance in relatively large molecular junction models. Our use of ABCs circumvents the demanding task of explicitly calculating the leads' self-energies from surface Green's functions, and is expected to be more accurate than the use of the jellium approximation. In addition, we take advantage of the sparsity in real space to solve efficiently for the Green's function over the entire energy range relevant to low-bias transport. We illustrate the advantages of our method with calculations on several challenging test systems and find good agreement with reference calculation results.
    Physical Review B 01/2014; 90(3). · 3.66 Impact Factor
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    ABSTRACT: A series of pseudosymmetrical structures of formula K10(M2OnF11-n)3X (M = V and Nb, n = 2, X = (F2Cl)1/3, Br, Br4/2,I4/2; M = Mo, n = 4, X = Cl, Br4/2, I4/2) illustrates generation of polar structures with the use of Λ-shaped basic building units (BBUs). For a compound to belong to a polar space group, dipole moments of individual species must be partially aligned. Incorporation of d(0) early transition metal polyhedral BBUs into structures is a common method to create polar structures, owing to the second-order Jahn-Teller distortion these polyhedra contain. Less attention has been spent examining how to align the polar moments of BBUs. To address alignment, we present a study on previously reported bimetallic BBUs and synthesized compounds K10(M2OnF11-n)3X. These materials differ in their (non)centrosymmetry despite chemical and structural similarities. The vanadium compounds are centrosymmetric (space groups P3̅m1 or C2/m) while the niobium and molybdenum heterotypes are noncentrosymmetric (Pmn21). The difference in symmetry occurs owing to the presence of linear, bimetallic BBUs or Λ-shaped bimetallic BBUs and related packing effects. These Λ-shaped BBUs form as a consequence of the coordination environment around the bridging anion of the metal oxide fluoride BBUs.
    Inorganic Chemistry 12/2013; · 4.59 Impact Factor
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    ABSTRACT: Tip-enhanced Raman spectroscopy (TERS) can probe chemistry occurring at surfaces with both nanometer spectroscopic and submolecular spatial resolution. Combining ultrafast spectroscopy with TERS allows for picosecond and, in principle, femtosecond temporal resolution. Here we couple an optical parametric oscillator (OPO) with a scanning tunneling microscopy (STM)-TERS microscope to excite the tip plasmon with a picosecond excitation source. The plasmonic tip was not damaged with OPO excitation, and TER spectra were observed for two resonant adsorbates. The TERS signal under ultrafast pulsed excitation decays on the time scale of 10 s of seconds; whereas with continuous-wave excitation no decay occurs. An analysis of possible decay mechanisms and their temporal characteristics is given.
    Journal of Physical Chemistry Letters 12/2013; 5(1):106–110. · 6.59 Impact Factor
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    ABSTRACT: The nonlinear optical dynamics of nano-materials comprised of plasmons interacting with quantum emitters is investigated by a self-consistent model based on the coupled Maxwell-Liouville-von Neumann equations. It is shown that ultra-short resonant laser pulses significantly modify the optical properties of such hybrid systems. It is further demonstrated that the energy transfer between interacting molecules and plasmons occurs on a femtosecond time scale and can be controlled with both material and laser parameters.
    ACS Nano 12/2013; · 12.03 Impact Factor
  • Amir Natan, Mark C Hersam, Tamar Seideman
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    ABSTRACT: Chemical modification of graphene is a common approach to control its electronic properties and hence fabricate electronic devices with new or improved functionalities. In this work we analyze, with density functional based calculations, the effect of chemical adsorption of fluorine atoms at different coverage levels on the electronic structure of graphene. We suggest a simple and general model for the shift of the Fermi level with coverage level and show the trends of the band gap and the Fermi level shift with coverage. We then show that the same model can be applied to explain the Fermi level shift in a different system of nitrogen substitution in graphene. Finally, we analyze the resulting charge transfer patterns and show that they are consistent with the model for the Fermi level shift.
    Nanotechnology 11/2013; 24(50):505715. · 3.84 Impact Factor
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    ABSTRACT: An explanation of the relative intensity fluctuations observed in single-molecule Raman experiments is described utilizing both single-molecule tip-enhanced Raman spectroscopy (SMTERS) and time-dependent density functional theory calculations (TD-DFT). No correlation is observed in mode to mode intensity fluctuations indicating that the changes in mode intensities are completely independent. Theoretical calculations provide convincing evidence that the fluctuations are not the result of diffusion, orientation, or local electromagnetic field gradients; but rather, are the result of subtle variations of the excited state lifetime, energy, and geometry of the molecule. These variations in the excited state properties will provide information on adsorbate-adsorbate and adsorbate-substrate interactions and may allow for inversion of experimental results to obtain these excited state properties.
    Journal of the American Chemical Society 09/2013; · 10.68 Impact Factor
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    ABSTRACT: We combine photoemission electron microscopy and electromagnetic simulations to describe the surface plasmon polariton dynamics following interaction of an ultrafast optical pulse with a slit coupling structure in a silver film. Through analysis of interference phenomena that lead to photoelectron emission from the silver film, we establish the universal contributions of a nanoscale asperity to the scattered surface field. Our results reveal the important role of surface cylindrical waves within the slit in the excitation of surface plasmon.
    The Journal of Physical Chemistry C. 08/2013; 117(36):18648–18652.
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    ABSTRACT: We study the order in which a strong laser field removes multiple electrons from a van der Waals (vdW) cluster. The N_{2}Ar, with an equilibrium T-shaped geometry, contains both a covalent and a vdW bond and serves as a simple yet rich example. Interestingly, the fragmenting double and triple ionizations of N_{2}Ar with vdW bond breaking are favored when the vdW bond is aligned along the laser field polarization vector. However, the orientation of the covalent bond with respect to the laser field rules the triple ionization when both the covalent and vdW bonds are simultaneously broken. Electron-localization-assisted enhanced ionization and molecular orbital profile-dominated, orientation-dependent ionization are discussed to reveal the order of electrons release from different sites of N_{2}Ar.
    Physical Review Letters 08/2013; 111(8):083003. · 7.73 Impact Factor
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    ABSTRACT: We present a model for strong field coherent control of torsional modes of molecules with a focus on exploring the controllability of molecular torsions subject to dissipative media and understanding how phase information is exchanged between torsional modes and a dissipative environment. Our theory is based on a density matrix formalism, wherein dissipation is accounted for within a multilevel Bloch equation model. Our results point to new and interesting phenomena in wavepacket dissipation dynamics that are unique to torsions and also enrich our general understanding of wavepacket phenomena. In addition, we suggest guidelines for designing torsional control experiments for molecules interacting with a dissipative bath.
    The Journal of Physical Chemistry C. 08/2013; 117(43):22391–22400.
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    ABSTRACT: We have developed an active-space decomposition strategy for molecular dimers that allows for the efficient computation of the dimer's complete-active-space wavefunction while only constructing the monomers' active-space wavefunctions. Dimer states are formed from linear combinations of direct products of localized orthogonal monomer states and Hamiltonian matrix elements are computed directly without explicitly constructing the product space. This decomposition is potentially exact in the limit where a full set of monomer states is included. The adiabatic states are then found by diagonalizing the dimer Hamiltonian matrix. We demonstrate the convergence of our method to a complete-active-space calculation of the full dimer with two test cases: the benzene and naphthalene dimers.
    The Journal of Chemical Physics 07/2013; 139(2):021108. · 3.12 Impact Factor

Publication Stats

4k Citations
881.66 Total Impact Points

Institutions

  • 2003–2014
    • Northwestern University
      • • Department of Chemistry
      • • Department of Materials Science and Engineering
      Evanston, Illinois, United States
  • 2013
    • Tel Aviv University
      Tell Afif, Tel Aviv, Israel
  • 2012
    • University of Colorado at Boulder
      • Department of Physics
      Boulder, CO, United States
  • 1987–2012
    • Weizmann Institute of Science
      • Department of Chemical Physics
      Israel
  • 2009
    • Universität Heidelberg
      • Interdisciplinary Center for Scientific Computing
      Heidelberg, Baden-Wuerttemberg, Germany
    • Arizona State University
      • Department of Applied Sciences and Mathematics
      Tempe, AZ, United States
  • 2008–2009
    • Freie Universität Berlin
      • Institute of Chemistry and Biochemistry
      Berlin, Land Berlin, Germany
  • 2004–2009
    • Aarhus University
      • • Department of Chemistry
      • • Department of Physics and Astronomy
      Aars, Region North Jutland, Denmark
  • 2000–2008
    • University of Chicago
      • Department of Chemistry
      Chicago, IL, United States
  • 2007
    • Paul Sabatier University - Toulouse III
      Tolosa de Llenguadoc, Midi-Pyrénées, France
    • Al-Quds University
      • Faculty of Pharmacy
      Abū Dīs, West Bank, Palestinian Territory
  • 2005
    • University of San Diego
      • Department of Physics
      San Diego, California, United States
    • RIKEN
      Вако, Saitama, Japan
  • 2000–2005
    • University of Illinois at Chicago
      • Department of Chemistry
      Chicago, IL, United States
  • 2002
    • McGill University
      • Department of Physics
      Montréal, Quebec, Canada
  • 1994–2002
    • National Research Council Canada
      • Steacie Institute for Molecular Sciences (SIMS)
      Ottawa, Ontario, Canada
  • 1997–1998
    • Harvard-Smithsonian Center for Astrophysics
      • Institute for Theoretical Atomic, Molecular and Optical Physics
      Boston, MA, United States
  • 1993–1994
    • University of California, Berkeley
      • Department of Chemistry
      Berkeley, CA, United States