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991.
Prashanth W. Menezes Carsten Walter Jan Niklas Hausmann Rodrigo Beltrn‐Suito Christopher Schlesiger Sebastian Praetz Valeriy Yu. Verchenko Andrei V. Shevelkov Matthias Driess 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(46):16722-16727
Erstmals wurden, in einen intermetallischen Vorläuferansatz, durch In‐situ‐Elektrokonversion von Mangangallid (MnGa4) hochleistungsfähige und langzeitstabile MnOx‐basierte Elektrokatalysatoren für die Wasseroxidation in alkalischem Medium hergestellt. Überraschend führt seine Elektrokorrosion, unter gleichzeitigem Verlust von Ga, gleichzeitig zu drei kristallinen Typen von MnOx‐Mineralien mit verschiedenen Strukturen und induzierten Defekten: Birnessit δ‐MnO2, Feitknechtit β‐MnOOH und Hausmannit α‐Mn3O4. Das Vorkommen und die intrinsische Stabilität von aktiven MnIII/MnIV‐Zentren in den drei gebildeten MnOx‐Phasen erklärt die hervorragende Effizienz und Stabilität des Systems für die elektrokatalytische Wasseroxidation. Nach der elektrophoretischen Abscheidung des MnGa4‐Vorläufers auf elektrisch leitfähigem Nickelschaum wurde ein niedriges Überpotential von 291 mV bei der Stromdichte von 10 mA cm?2 erreicht, das praktisch den Überpotentialen von edelmetallbasierten Katalysatoren entspricht und für mehr als fünf Tage beständig ist. 相似文献
992.
Kristina O. Kvashnina Anna Yu. Romanchuk Ivan Pidchenko Lucia Amidani Evgeny Gerber Alexander Trigub Andre Rossberg Stephan Weiss Karin Popa Olaf Walter Roberto Caciuffo Andreas C. Scheinost Sergei M. Butorin Stepan N. Kalmykov 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(49):18044-18044
993.
Jeaphianne P. M. van Rijn Andrés M. Escorcia Walter Thiel 《Journal of computational chemistry》2019,40(21):1902-1910
Combined quantum mechanics/molecular mechanics (QM/MM) calculations were used to investigate the reaction mechanism of taxadiene synthase (TXS). TXS catalyzes the cyclization of geranylgeranyl diphosphate (GGPP) to taxadiene (T) and four minor cyclic products. All these products originate from the deprotonation of carbocation intermediates. The reaction profiles for the conversion of GGPP to T as well as to minor products were calculated for different configurations of relevant TXS carbocation complexes. The QM region was treated at the M06-2X/TZVP level, while the CHARMM27 force field was used to describe the MM region. The QM/MM calculations suggest a reaction pathway for the conversion of GGPP to T, which slightly differs from previous proposals regarding the number of reaction steps and the conformation of the carbocations. The QM/MM results also indicate that the formation of minor products via water-assisted deprotonation of the carbocations is highly exothermic, by about −7 to −23 kcal/mol. Curiously, however, the computed barriers and reaction energies indicate that the formation of some of the minor products is more facile than the formation of T. Thus, the present QM/MM calculations provide detailed insights into possible reaction pathways and into the origin of the promiscuity of TXS, but they do not reproduce the product distribution observed experimentally. © 2019 Wiley Periodicals, Inc. 相似文献
994.
We present a theory of low-frequency Raman scattering in glasses, based on the concept that light couples to the elastic strains via spatially fluctuating elasto-optic (Pockels) constants. We show that the Raman intensity is not proportional to the vibrational density of states (as was widely believed), but to a convolution of Pockels constant correlation functions with the dynamic strain susceptibilities of the glass. Using the dynamic susceptibilities of a system with fluctuating elastic constants we are able for the first time to describe the Raman intensity and the anomalous vibration spectrum of a glass on the same footing. Good agreement between the theory and experiment for the Raman spectrum, the density of states, and the specific heat is demonstrated at the example of glassy As(2)S(3). 相似文献
995.
It is known that perturbation theory converges in fermionic field theory at weak coupling if the interaction and the covariance are summable and if certain determinants arising in the expansion can be bounded efficiently, e.g. if the covariance admits a Gram representation with a finite Gram constant. The covariances of the standard many–fermion systems do not fall into this class due to the slow decay of the covariance at large Matsubara frequency, giving rise to a UV problem in the integration over degrees of freedom with Matsubara frequencies larger than some Ω (usually the first step in a multiscale analysis). We show that these covariances do not have Gram representations on any separable Hilbert space. We then prove a general bound for determinants associated to chronological products which is stronger than the usual Gram bound and which applies to the many–fermion case. This allows us to prove convergence of the first integration step in a rather easy way, for a short–range interaction which can be arbitrarily strong, provided Ω is chosen large enough. Moreover, we give – for the first time – nonperturbative bounds on all scales for the case of scale decompositions of the propagator which do not impose cutoffs on the Matsubara frequency. 相似文献
996.
We investigate the time-dependent Kondo effect in a single-molecule magnet (SMM) strongly coupled to metallic electrodes. Describing the SMM by a Kondo model with large spin S>1/2, we analyze the underscreening of the local moment and the effect of anisotropy terms on the relaxation dynamics of the magnetization. Underscreening by single-channel Kondo processes leads to a logarithmically slow relaxation, while finite uniaxial anisotropy causes a saturation of the SMM's magnetization. Additional transverse anisotropy terms induce quantum spin tunneling and a pseudospin-1/2 Kondo effect sensitive to the spin parity. 相似文献
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Numerical Algorithms - The first equation in Eq. (2.9) should read 相似文献