Journal: Structural Dynamics

Abbreviation

Struct. Dyn.

Publisher

American Institute of Physics

Journal Volumes

ISSN

2329-7778

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2014 - 2019192020 - 202512
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Publications 1 - 10 of 31
  • Charge migration and charge transfer in molecular systems
    Item type: Review Article
    Wörner, Hans Jakob; Arrell, Christopher; Banerji, Natalie; et al. (2017)
    Structural Dynamics
    The transfer of charge at the molecular level plays a fundamental role in many areas of chemistry, physics, biology and materials science. Today, more than 60 years after the seminal work of R. A. Marcus, charge transfer is still a very active field of research. An important recent impetus comes from the ability to resolve ever faster temporal events, down to the attosecond time scale. Such a high temporal resolution now offers the possibility to unravel the most elementary quantum dynamics of both electrons and nuclei that participate in the complex process of charge transfer. This review covers recent research that addresses the following questions. Can we reconstruct the migration of charge across a molecule on the atomic length and electronic time scales? Can we use strong laser fields to control charge migration? Can we temporally resolve and understand intramolecular charge transfer in dissociative ionization of small molecules, in transition-metal complexes and in conjugated polymers? Can we tailor molecular systems towards specific charge-transfer processes? What are the time scales of the elementary steps of charge transfer in liquids and nanoparticles? Important new insights into each of these topics, obtained from state-of-the-art ultrafast spectroscopy and/or theoretical methods, are summarized in this review.
  • Localized holes and delocalized electrons in photoexcited inorganic perovskites: Watching each atomic actor by picosecond X-ray absorption spectroscopy
    Item type: Journal Article
    Santomauro, Fabio G.; Grilj, Jakob; Mewes, Lars; et al. (2017)
    Structural Dynamics
    We report on an element-selective study of the fate of charge carriers in photoexcited inorganic CsPbBr3 and CsPb(ClBr)3 perovskite nanocrystals in toluene solutions using time-resolved X-ray absorption spectroscopy with 80 ps time resolution. Probing the Br K-edge, the Pb L3-edge, and the Cs L2-edge, we find that holes in the valence band are localized at Br atoms, forming small polarons, while electrons appear as delocalized in the conduction band. No signature of either electronic or structural changes is observed at the Cs L2-edge. The results at the Br and Pb edges suggest the existence of a weakly localized exciton, while the absence of signatures at the Cs edge indicates that the Cs+ cation plays no role in the charge transport, at least beyond 80 ps. This first, time-resolved element-specific study of perovskites helps understand the rather modest charge carrier mobilities in these materials.
  • Dynamics of the photoinduced insulator-to-metal transition in a nickelate film
    Item type: Journal Article
    Esposito, Vincent; Rettig, Laurenz; Bothschafter, Elisabeth M.; et al. (2018)
    Structural Dynamics
    Material properties can be controlled via strain, pressure, chemical composition, or dimensionality. Nickelates are particularly susceptible due to their strong variations of the electronic and magnetic properties on such external stimuli. Here, we analyze the photoinduced dynamics in a single crystalline NdNiO3 film upon excitation across the electronic gap. Using time-resolved reflectivity and resonant x-ray diffraction, we show that the pump pulse induces an insulator-to-metal transition, accompanied by the melting of the charge order. Finally, we compare our results with similar studies in manganites and show that the same model can be used to describe the dynamics in nickelates, hinting towards a unified description of these photoinduced electronic ordering phase transitions.
  • Communication: The electronic structure of matter probed with a single femtosecond hard x-ray pulse
    Item type: Journal Article
    Szlachetko, Jakub; Milne, Chris; Hoszowska, Joanna; et al. (2014)
    Structural Dynamics
    Physical, biological, and chemical transformations are initiated by changes in theelectronic configuration of the species involved. These electronic changes occur onthe timescales of attoseconds (10-18s) to femtoseconds (10-15s) and drive allsubsequent electronic reorganization as the system moves to a new equilibrium orquasi-equilibrium state. The ability to detect the dynamics of these electronicchanges is crucial for understanding the potential energy surfaces upon whichchemical and biological reactions take place. Here, we report on the determinationof the electronic structure of matter using a single self-seeded femtosecond x-raypulse from the Linac Coherent Light Source hard x-ray free electron laser. Bymeasuring the high energy resolution off-resonant spectrum (HEROS), we wereable to obtain information about the electronic density of states with a singlefemtosecond x-ray pulse. We show that the unoccupied electronic states of thescattering atom may be determined on a shot-to-shot basis and that the measuredspectral shape is independent of the large intensity fluctuations of the incomingx-ray beam. Moreover, we demonstrate the chemical sensitivity and single-shotcapability and limitations of HEROS, which enables the technique to track theelectronic structural dynamics in matter on femtosecond time scales, making it anideal probe technique for time-resolved X-ray experiments.
  • Kinetic isotope effects and how to describe them
    Item type: Journal Article
    Karandashev, Konstantin; Xu, Zhen-Hao; Meuwly, Markus; et al. (2017)
    Structural Dynamics
    We review several methods for computing kinetic isotope effects in chemical reactions including semiclassical and quantum instanton theory. These methods describe both the quantization of vibrational modes as well as tunneling and are applied to the H + H2 and H + CH4 reactions. The absolute rate constants computed with the semiclassical instanton method both using on-the-fly electronic structure calculations and fitted potential-energy surfaces are also compared directly with exact quantum dynamics results. The error inherent in the instanton approximation is found to be relatively small and similar in magnitude to that introduced by using fitted surfaces. The kinetic isotope effect computed by the quantum instanton is even more accurate, and although it is computationally more expensive, the efficiency can be improved by path-integral acceleration techniques. We also test a simple approach for designing potential-energy surfaces for the example of proton transfer in malonaldehyde. The tunneling splittings are computed, and although they are found to deviate from experimental results, the ratio of the splitting to that of an isotopically substituted form is in much better agreement. We discuss the strengths and limitations of the potential-energy surface and based on our findings suggest ways in which it can be improved.
  • Preface to Special Topic: Invited Papers of the 3rd International Conference on Ultrafast Structural Dynamics
    Item type: Other Journal Item
    Johnson, Steven (2016)
    Structural Dynamics
    The ability to visualize the real-time dynamics of atomic, magnetic, and electronicstructure is widely recognized in many fields as a key element underpinning manyimportant processes in chemistry, materials science, and biology. The need for animproved understanding of such processes becomes acute as energy conversion proc-esses on fast time scales become increasingly relevant to problems in science andtechnology. This special issue, containing invited papers from participants at the 3rdInternational Conference on Ultrafast Structural Dynamics held June 10–12, 2015 inZurich, Switzerland, discusses several recent developments in this area.
  • Dynamics retrieval from stochastically weighted incomplete data by low-pass spectral analysis
    Item type: Journal Article
    Casadei, Cecilia M.; Hosseinizadeh, Ahmad; Schertler, Gebhard F.X.; et al. (2022)
    Structural Dynamics
    ABSTRACT Time-resolved serial femtosecond crystallography (TR-SFX) provides access to protein dynamics on sub-picosecond timescales, and with atomic resolution. Due to the nature of the experiment, these datasets are often highly incomplete and the measured diffracted intensities are affected by partiality. To tackle these issues, one established procedure is that of splitting the data into time bins, and averaging the multiple measurements of equivalent reflections within each bin. This binning and averaging often involve a loss of information. Here, we propose an alternative approach, which we call low-pass spectral analysis (LPSA). In this method, the data are projected onto the subspace defined by a set of trigonometric functions, with frequencies up to a certain cutoff. This approach attenuates undesirable high-frequency features and facilitates retrieving the underlying dynamics. A time-lagged embedding step can be included prior to subspace projection to improve the stability of the results with respect to the parameters involved. Subsequent modal decomposition allows to produce a low-rank description of the system's evolution. Using a synthetic time-evolving model with incomplete and partial observations, we analyze the LPSA results in terms of quality of the retrieved signal, as a function of the parameters involved. We compare the performance of LPSA to that of a range of other sophisticated data analysis techniques. We show that LPSA allows to achieve excellent dynamics reconstruction at modest computational cost. Finally, we demonstrate the superiority of dynamics retrieval by LPSA compared to time binning and merging, which is, to date, the most commonly used method to extract dynamical information from TR-SFX data.
  • Preface to Swiss National Center of Competence in Research: Molecular Ultrafast Science and Technology
    Item type: Journal Article
    Feurer, Thomas; Keller, Ursula (2017)
    Structural Dynamics
  • Low-pass spectral analysis of time-resolved serial femtosecond crystallography data
    Item type: Journal Article
    Casadei, Cecilia M.; Hosseinizadeh, Ahmad; Bliven, Spencer; et al. (2023)
    Structural Dynamics
    Low-pass spectral analysis (LPSA) is a recently developed dynamics retrieval algorithm showing excellent retrieval properties when applied to model data affected by extreme incompleteness and stochastic weighting. In this work, we apply LPSA to an experimental time-resolved serial femtosecond crystallography (TR-SFX) dataset from the membrane protein bacteriorhodopsin (bR) and analyze its parametric sensitivity. While most dynamical modes are contaminated by nonphysical high-frequency features, we identify two dominant modes, which are little affected by spurious frequencies. The dynamics retrieved using these modes shows an isomerization signal compatible with previous findings. We employ synthetic data with increasing timing uncertainty, increasing incompleteness level, pixel-dependent incompleteness, and photon counting errors to investigate the root cause of the high-frequency contamination of our TR-SFX modes. By testing a range of methods, we show that timing errors comparable to the dynamical periods to be retrieved produce a smearing of dynamical features, hampering dynamics retrieval, but with no introduction of spurious components in the solution, when convergence criteria are met. Using model data, we are able to attribute the high-frequency contamination of low-order dynamical modes to the high levels of noise present in the data. Finally, we propose a method to handle missing observations that produces a substantial dynamics retrieval improvement from synthetic data with a significant static component. Reprocessing of the bR TR-SFX data using the improved method yields dynamical movies with strong isomerization signals compatible with previous findings.
  • Magnetization dynamics: From the Landau-Lifschitz equation to spintronics
    Item type: Journal Article
    Acremann, Yves Marc (2025)
    Structural Dynamics
    Magnetic storage devices are still an essential part of our information society, and magnetic random access memory could bridge the gap between storage and memory devices. Jo Stöhr pioneered the study of magnetism and its dynamics by time-resolved x-ray microscopy and spectroscopy. In this paper, we focus on the applied aspects of spin dynamics and on how time-resolved circular dichroism and x-ray microscopy helped develop magnetic random access memory.
Publications 1 - 10 of 31