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Alexander Eisfeld - One of the best experts on this subject based on the ideXlab platform.
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charge and energy transfer in large molecular assemblies quantum State Diffusion with an adaptive basis
Journal of Chemical Physics, 2019Co-Authors: Alexander EisfeldAbstract:We show that the stochastic, wave-function based quantum State Diffusion approach in combination with an adaptive basis is well suited to numerically treat the motion of an excitation in large molecular aggregates in the complicated regime where the transfer-time between molecules is comparable to the decoherence caused by environmental degrees of freedom.We show that the stochastic, wave-function based quantum State Diffusion approach in combination with an adaptive basis is well suited to numerically treat the motion of an excitation in large molecular aggregates in the complicated regime where the transfer-time between molecules is comparable to the decoherence caused by environmental degrees of freedom.
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non markovian quantum State Diffusion for temperature dependent linear spectra of light harvesting aggregates
arXiv: Chemical Physics, 2014Co-Authors: Gerhard Ritschel, Daniel Suess, S Mobius, Walter T Strunz, Alexander EisfeldAbstract:Non-Markovian Quantum State Diffusion (NMQSD) has turned out to be an efficient method to calculate excitonic properties of aggregates composed of organic chromophores, taking into account the coupling of electronic transitions to vibrational modes of the chromophores. NMQSD is an open quantum system approach that incorporates environmental degrees of freedom (the vibrations in our case) in a stochastic way. We show in this paper that for linear optical spectra (absorption, circular dichroism) no stochastics is needed, even for finite temperatures. Thus, the spectra can be obtained by propagating a single trajectory. To this end we map a finite temperature environment to the zero temperature case using the so-called thermofield method. The resulting equations can then be solved efficiently by standard integrators.
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non markovian quantum State Diffusion for absorption spectra of molecular aggregates
Journal of Chemical Physics, 2011Co-Authors: Jan Roden, Walter T Strunz, Alexander EisfeldAbstract:In many molecular systems one encounters the situation where electronic excitations couple to a quasi-continuum of phonon modes. The interaction to that often structured continuum may be highly frequency dependent, e.g. due to some weakly damped high frequency modes. To handle such a situation, an approach combining the non-Markovian quantum State Diffusion description of open quantum systems with an efficient but abstract approximation was recently applied to calculate energy transfer and absorption spectra of molecular aggregates [J. Roden, A. Eisfeld, W. Wolff, W. T. Strunz, Phys. Rev. Lett. 103, 058301 (2009)]. To explore the validity of the used approximation for such complicated systems, in the present work we compare the calculated (approximative) absorption spectra with exact results. These are obtained from the method of pseudomodes, which we show to be capable of determining the exact spectra for small aggregates and a few pseudomodes. It turns out that in the cases considered, the results of the two approaches mostly agree quite well. The advantages and disadvantages of the two approaches are discussed.
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spectral properties of molecular oligomers a non markovian quantum State Diffusion approach
International Journal of Modern Physics B, 2010Co-Authors: Jan Roden, Walter T Strunz, Alexander EisfeldAbstract:Absorption spectra of small molecular aggregates (oligomers) are considered. The dipole-dipole interaction between the monomers leads to shifts of the oligomer spectra with respect to the monomer absorption. The line-shapes of monomer as well as oligomer absorption depend strongly on the coupling to vibrational modes. Using a recently developed approach [Roden et al., PRL 103, 058301] we investigate the length dependence of spectra of one-dimensional aggregates for various values of the interaction strength between the monomers. It is demonstrated, that the present approach is well suited to describe the occurrence of the J- and H-bands.
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non markovian quantum State Diffusion for absorption spectra of molecular aggregates
arXiv: Quantum Physics, 2010Co-Authors: Jan Roden, Walter T Strunz, Alexander EisfeldAbstract:In many molecular systems one encounters the situation where electronic excitations couple to a quasi-continuum of phonon modes. That continuum may be highly structured e.g. due to some weakly damped high frequency modes. To handle such a situation, an approach combining the non-Markovian quantum State Diffusion (NMQSD) description of open quantum systems with an efficient but abstract approximation was recently applied to calculate energy transfer and absorption spectra of molecular aggregates [Roden, Eisfeld, Wolff, Strunz, PRL 103 (2009) 058301]. To explore the validity of the used approximation for such complicated systems, in the present work we compare the calculated (approximative) absorption spectra with exact results. These are obtained from the method of pseudomodes, which we show to be capable of determining the exact spectra for small aggregates and a few pseudomodes. It turns out that in the cases considered, the results of the two approaches mostly agree quite well. The advantages and disadvantages of the two approaches are discussed.
Shun Watanabe - One of the best experts on this subject based on the ideXlab platform.
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2d coherent charge transport in highly ordered conducting polymers doped by solid State Diffusion
Nature Materials, 2016Co-Authors: Keehoon Kang, Katharina Broch, Shun Watanabe, Alessandro Sepe, Adam J Brown, Iyad Nasrallah, Mark Nikolka, Zhuping FeiAbstract:Doping is one of the most important methods to control charge carrier concentration in semiconductors. Ideally, the introduction of dopants should not perturb the ordered microstructure of the semiconducting host. In some systems, such as modulation-doped inorganic semiconductors or molecular charge transfer crystals, this can be achieved by spatially separating the dopants from the charge transport pathways. However, in conducting polymers, dopants tend to be randomly distributed within the conjugated polymer, and as a result the transport properties are strongly affected by the resulting structural and electronic disorder. Here, we show that in the highly ordered lamellar microstructure of a regioregular thiophene-based conjugated polymer, a small-molecule p-type dopant can be incorporated by solid State Diffusion into the layers of solubilizing side chains without disrupting the conjugated layers. In contrast to more disordered systems, this allows us to observe coherent, free-electron-like charge transport properties, including a nearly ideal Hall effect in a wide temperature range, a positive magnetoconductance due to weak localization and the Pauli paramagnetic spin susceptibility.
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2d coherent charge transport in highly ordered conducting polymers doped by solid State Diffusion
Nature Materials, 2016Co-Authors: Keehoon Kang, Katharina Broch, Shun Watanabe, Alessandro Sepe, Adam J Brown, Iyad Nasrallah, Mark Nikolka, Martin HeeneyAbstract:Small molecules diffusing into a thin film of thiophene-based conjugated polymers act as p-type dopants without altering the ordered microstructure of the film. As a result, free-electron-like charge transport is also observed at high doping levels.
Walter T Strunz - One of the best experts on this subject based on the ideXlab platform.
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non markovian quantum State Diffusion for temperature dependent linear spectra of light harvesting aggregates
arXiv: Chemical Physics, 2014Co-Authors: Gerhard Ritschel, Daniel Suess, S Mobius, Walter T Strunz, Alexander EisfeldAbstract:Non-Markovian Quantum State Diffusion (NMQSD) has turned out to be an efficient method to calculate excitonic properties of aggregates composed of organic chromophores, taking into account the coupling of electronic transitions to vibrational modes of the chromophores. NMQSD is an open quantum system approach that incorporates environmental degrees of freedom (the vibrations in our case) in a stochastic way. We show in this paper that for linear optical spectra (absorption, circular dichroism) no stochastics is needed, even for finite temperatures. Thus, the spectra can be obtained by propagating a single trajectory. To this end we map a finite temperature environment to the zero temperature case using the so-called thermofield method. The resulting equations can then be solved efficiently by standard integrators.
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non markovian quantum State Diffusion for absorption spectra of molecular aggregates
Journal of Chemical Physics, 2011Co-Authors: Jan Roden, Walter T Strunz, Alexander EisfeldAbstract:In many molecular systems one encounters the situation where electronic excitations couple to a quasi-continuum of phonon modes. The interaction to that often structured continuum may be highly frequency dependent, e.g. due to some weakly damped high frequency modes. To handle such a situation, an approach combining the non-Markovian quantum State Diffusion description of open quantum systems with an efficient but abstract approximation was recently applied to calculate energy transfer and absorption spectra of molecular aggregates [J. Roden, A. Eisfeld, W. Wolff, W. T. Strunz, Phys. Rev. Lett. 103, 058301 (2009)]. To explore the validity of the used approximation for such complicated systems, in the present work we compare the calculated (approximative) absorption spectra with exact results. These are obtained from the method of pseudomodes, which we show to be capable of determining the exact spectra for small aggregates and a few pseudomodes. It turns out that in the cases considered, the results of the two approaches mostly agree quite well. The advantages and disadvantages of the two approaches are discussed.
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spectral properties of molecular oligomers a non markovian quantum State Diffusion approach
International Journal of Modern Physics B, 2010Co-Authors: Jan Roden, Walter T Strunz, Alexander EisfeldAbstract:Absorption spectra of small molecular aggregates (oligomers) are considered. The dipole-dipole interaction between the monomers leads to shifts of the oligomer spectra with respect to the monomer absorption. The line-shapes of monomer as well as oligomer absorption depend strongly on the coupling to vibrational modes. Using a recently developed approach [Roden et al., PRL 103, 058301] we investigate the length dependence of spectra of one-dimensional aggregates for various values of the interaction strength between the monomers. It is demonstrated, that the present approach is well suited to describe the occurrence of the J- and H-bands.
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non markovian quantum State Diffusion for absorption spectra of molecular aggregates
arXiv: Quantum Physics, 2010Co-Authors: Jan Roden, Walter T Strunz, Alexander EisfeldAbstract:In many molecular systems one encounters the situation where electronic excitations couple to a quasi-continuum of phonon modes. That continuum may be highly structured e.g. due to some weakly damped high frequency modes. To handle such a situation, an approach combining the non-Markovian quantum State Diffusion (NMQSD) description of open quantum systems with an efficient but abstract approximation was recently applied to calculate energy transfer and absorption spectra of molecular aggregates [Roden, Eisfeld, Wolff, Strunz, PRL 103 (2009) 058301]. To explore the validity of the used approximation for such complicated systems, in the present work we compare the calculated (approximative) absorption spectra with exact results. These are obtained from the method of pseudomodes, which we show to be capable of determining the exact spectra for small aggregates and a few pseudomodes. It turns out that in the cases considered, the results of the two approaches mostly agree quite well. The advantages and disadvantages of the two approaches are discussed.
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non markovian quantum State Diffusion
Physical Review A, 1998Co-Authors: Lajos Diosi, Nicolas Gisin, Walter T StrunzAbstract:A nonlinear stochastic Schr\"odinger equation for pure States describing non-Markovian Diffusion of quantum trajectories and compatible with non-Markovian master equations is presented. This provides an unraveling of the evolution of any quantum system coupled to a finite or infinite number of harmonic oscillators without any approximation. Its power is illustrated by several examples, including measurementlike situations, dissipation, and quantum Brownian motion. Some examples treat this environment phenomenologically as an infinite reservoir with fluctuations of arbitrary correlation. In other examples the environment consists of a finite number of oscillators. In such a quasiperiodic case we see the reversible decay of a macroscopic quantum-superposition (``Schr\"odinger cat''). Finally, our description of open systems is compatible with different positions of the ``Heisenberg cut'' between system and environment.
I Karaman - One of the best experts on this subject based on the ideXlab platform.
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interfacial study of niti ti3sic2 solid State Diffusion bonded joints
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2015Co-Authors: Ankush Kothalkar, Afşin Cerit, Gwenaelle Proust, Sandip Basu, Miladin Radovic, I KaramanAbstract:Abstract The interfaces between the stress-assisted Diffusion bonded Ti3SiC2 and equiatomic NiTi, two distinct material systems that show pseudoelasticity were studied. The interfaces were formed in the 800–1000 °C temperature range, for 1, 5 and 10 h under flowing argon. Bonding was observed in all the cases considered, except at 800 °C after 1 h. Morphology and reaction phases in the interface were characterized using scanning electron microscopy, elemental micro probe analysis and electron backscatter diffraction analysis. The interfacial structure formed between NiTi and Ti3SiC2 layers consists of NiTi/Ti2Ni/Ti5Si3/NiTiSi/Ti3SiC2. Diffusion of Si into NiTi from Ti3SiC2, and Ni from NiTi into reaction zone was found to be responsible for the formation of reaction layers in the interface and thus for bonding at these conditions. The overall reaction layer thickness grows following the parabolic kinetic law. Nano-indentation and Vickers micro hardness tests were carried out to investigate the mechanical properties of the interface. Nano-indentation showed that the elastic moduli of the phases in the interface are close to that of Ti3SiC2 while their hardness is higher than that of both Ti3SiC2 and NiTi. Artificially formed cracks through microindents were observed to be branched and propagated into Ti3SiC2 phase indicating good resistance against delamination.
Yuan Yuan - One of the best experts on this subject based on the ideXlab platform.
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investigation of Diffusion behavior in cu sn solid State Diffusion couples
Journal of Alloys and Compounds, 2016Co-Authors: Yuan Yuan, Yuanyuan Guan, Nele MoelansAbstract:Abstract The Diffusion behaviors and Diffusion parameters of intermetallic compounds (IMCs) formed in Cu–Sn Diffusion couples were investigated at the temperature range of 130 °C–200 °C. InterDiffusion coefficients of IMCs were calculated based on the measured composition profiles of the Diffusion zones. Considering the wavy type of the Diffusion layers and the narrow homogeneity range of the IMCs (Cu3Sn and Cu6Sn5), the integrated method was performed to evaluate the integrated interDiffusion coefficients based on the measured thicknesses of the IMCs layers. The transient initial growth stage was excluded by considering two Diffusion times where the growths of both IMCs are in the Diffusion control stage. The activation energies for Diffusion of the IMCs were evaluated from the integrated Diffusion coefficients. The growth behavior of Cu3Sn suggested the existence of a transient growth regime for Cu3Sn at the initial stage in cold-bonded Cu–Sn Diffusion couple. The intrinsic Diffusion coefficients of Cu and Sn in Cu6Sn5 were estimated based on the integrated Diffusion coefficients. Sn was found to be the faster Diffusion component in the Cu6Sn5 phase. Phase-field simulations combined with the experimentally measured Diffusion coefficients and steady-State growth-rate coefficients were performed to estimate the homogeneity range of IMCs. The estimated results are consistent with the experimental results from this study as well as those from literature experimental values and showed that the homogeneity ranges of Cu3Sn and Cu6Sn5 phases in the Cu–Sn system are almost temperature independent.
