TY - JOUR A1 - Fritsch, Daniel T1 - Revisiting the Cu-Zn disorder in kesterite type Cu2ZnSnSe4 employing a novel approach to hybrid functional calculations JF - Applied Sciences : open access journal N2 - In recent years, the search for more efficient and environmentally friendly materials to be employed in the next generation of thin film solar cell devices has seen a shift towards hybrid halide perovskites and chalcogenide materials crystallising in the kesterite crystal structure. Prime examples for the latter are Cu2ZnSnS4, Cu2ZnSnSe4, and their solid solution Cu2ZnSn(SxSe1-x)(4), where actual devices already demonstrated power conversion efficiencies of about 13 %. However, in their naturally occurring kesterite crystal structure, the so-called Cu-Zn disorder plays an important role and impacts the structural, electronic, and optical properties. To understand the influence of Cu-Zn disorder, we perform first-principles calculations based on density functional theory combined with special quasirandom structures to accurately model the cation disorder. Since the electronic band gaps and derived optical properties are severely underestimated by (semi)local exchange and correlation functionals, supplementary hybrid functional calculations have been performed. Concerning the latter, we additionally employ a recently devised technique to speed up structural relaxations for hybrid functional calculations. Our calculations show that the Cu-Zn disorder leads to a slight increase in the unit cell volume compared to the conventional kesterite structure showing full cation order, and that the band gap gets reduced by about 0.2 eV, which is in very good agreement with earlier experimental and theoretical findings. Our detailed results on structural, electronic, and optical properties will be discussed with respect to available experimental data, and will provide further insights into the atomistic origin of the disorder-induced band gap lowering in these promising kesterite type materials. KW - Cu2ZnSnSe4 KW - CZTSe KW - chalcogenide KW - kesterite KW - Cu-Zn disorder KW - density KW - functional theory KW - hybrid functional KW - special quasirandom structure Y1 - 2022 U6 - https://doi.org/10.3390/app12052576 SN - 2076-3417 VL - 12 IS - 5 PB - MDPI CY - Basel ER - TY - JOUR A1 - Jay, Raphael M. A1 - Vaz da Cruz, Vinicius A1 - Eckert, Sebastian A1 - Fondell, Mattis A1 - Mitzner, Rolf A1 - Föhlisch, Alexander T1 - Probing solute-solvent interactions of transition metal complexes using L-edge absorption spectroscopy JF - The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces & biophysical chemistry N2 - In order to tailor solution-phase chemical reactions involving transition metal complexes, it is critical to understand how their valence electronic charge distributions are affected by the solution environment. Here, solute-solvent interactions of a solvatochromic mixed-ligand iron complex were investigated using X-ray absorption spectroscopy at the transition metal L-2,L-3-edge. Due to the selectivity of the corresponding core excitations to the iron 3d orbitals, the method grants direct access to the valence electronic structure around the iron center and its response to interactions with the solvent environment. A linear increase of the total L-2,L-3-edge absorption cross section as a function of the solvent Lewis acidity is revealed. The effect is caused by relative changes in different metal-ligand-bonding channels, which preserve local charge densities while increasing the density of unoccupied states around the iron center. These conclusions are corroborated by a combination of molecular dynamics and spectrum simulations based on time-dependent density functional theory. The simulations reproduce the spectral trends observed in the X-ray but also optical absorption experiments. Our results underscore the importance of solute-solvent interactions when aiming for an accurate description of the valence electronic structure of solvated transition metal complexes and demonstrate how L-2,L-3-edge absorption spectroscopy can aid in understanding the impact of the solution environment on intramolecular covalency and the electronic charge distribution. KW - basis-sets KW - charge-transfer KW - density KW - dynamics KW - electron localization KW - iron KW - solvation KW - spin-crossover KW - tranfer excited-state KW - x-ray-absorption Y1 - 2020 U6 - https://doi.org/10.1021/acs.jpcb.0c00638 SN - 1520-6106 SN - 1520-5207 VL - 124 IS - 27 SP - 5636 EP - 5645 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Cervantes, Sebastian A1 - Shprits, Yuri Y. A1 - Aseev, Nikita A1 - Drozdov, Alexander A1 - Castillo Tibocha, Angelica Maria A1 - Stolle, Claudia T1 - Identifying radiation belt electron source and loss processes by assimilating spacecraft data in a three-dimensional diffusion model JF - Journal of geophysical research : Space physics N2 - Data assimilation aims to blend incomplete and inaccurate data with physics-based dynamical models. In the Earth's radiation belts, it is used to reconstruct electron phase space density, and it has become an increasingly important tool in validating our current understanding of radiation belt dynamics, identifying new physical processes, and predicting the near-Earth hazardous radiation environment. In this study, we perform reanalysis of the sparse measurements from four spacecraft using the three-dimensional Versatile Electron Radiation Belt diffusion model and a split-operator Kalman filter over a 6-month period from 1 October 2012 to 1 April 2013. In comparison to previous works, our 3-D model accounts for more physical processes, namely, mixed pitch angle-energy diffusion, scattering by Electromagnetic Ion Cyclotron waves, and magnetopause shadowing. We describe how data assimilation, by means of the innovation vector, can be used to account for missing physics in the model. We use this method to identify the radial distances from the Earth and the geomagnetic conditions where our model is inconsistent with the measured phase space density for different values of the invariants mu and K. As a result, the Kalman filter adjusts the predictions in order to match the observations, and we interpret this as evidence of where and when additional source or loss processes are active. The current work demonstrates that 3-D data assimilation provides a comprehensive picture of the radiation belt electrons and is a crucial step toward performing reanalysis using measurements from ongoing and future missions. KW - acceleration KW - code KW - density KW - emic waves KW - energetic particle KW - mechanisms KW - reanalysis KW - ultrarelativistic electrons KW - weather Y1 - 2019 U6 - https://doi.org/10.1029/2019JA027514 SN - 2169-9380 SN - 2169-9402 VL - 125 IS - 1 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Lehmann, Anika A1 - Zheng, Weishuang A1 - Ryo, Masahiro A1 - Soutschek, Katharina A1 - Roy, Julien A1 - Rongstock, Rebecca A1 - Maaß, Stefanie A1 - Rillig, Matthias C. T1 - Fungal traits important for soil aggregation JF - Frontiers in microbiology N2 - Soil structure, the complex arrangement of soil into aggregates and pore spaces, is a key feature of soils and soil biota. Among them, filamentous saprobic fungi have well-documented effects on soil aggregation. However, it is unclear what properties, or traits, determine the overall positive effect of fungi on soil aggregation. To achieve progress, it would be helpful to systematically investigate a broad suite of fungal species for their trait expression and the relation of these traits to soil aggregation. Here, we apply a trait-based approach to a set of 15 traits measured under standardized conditions on 31 fungal strains including Ascomycota, Basidiomycota, and Mucoromycota, all isolated from the same soil. We find large differences among these fungi in their ability to aggregate soil, including neutral to positive effects, and we document large differences in trait expression among strains. We identify biomass density, i.e., the density with which a mycelium grows (positive effects), leucine aminopeptidase activity (negative effects) and phylogeny as important factors explaining differences in soil aggregate formation (SAF) among fungal strains; importantly, growth rate was not among the important traits. Our results point to a typical suite of traits characterizing fungi that are good soil aggregators, and our findings illustrate the power of employing a trait-based approach to unravel biological mechanisms underpinning soil aggregation. Such an approach could now be extended also to other soil biota groups. In an applied context of restoration and agriculture, such trait information can inform management, for example to prioritize practices that favor the expression of more desirable fungal traits. KW - soil aggregation KW - traits KW - saprobic fungi KW - random forest KW - biomass KW - density KW - leucine amino peptidases Y1 - 2020 U6 - https://doi.org/10.3389/fmicb.2019.02904 SN - 1664-302X VL - 10 PB - Frontiers Media CY - Lausanne ER - TY - JOUR A1 - Awad, Emad A1 - Metzler, Ralf T1 - Closed-form multi-dimensional solutions and asymptotic behaviours for subdiffusive processes with crossovers: II. Accelerating case JF - Journal of physics : A, Mathematical and theoretical N2 - Anomalous diffusion with a power-law time dependence vertical bar R vertical bar(2)(t) similar or equal to t(alpha i) of the mean squared displacement occurs quite ubiquitously in numerous complex systems. Often, this anomalous diffusion is characterised by crossovers between regimes with different anomalous diffusion exponents alpha(i). Here we consider the case when such a crossover occurs from a first regime with alpha(1) to a second regime with alpha(2) such that alpha(2) > alpha(1), i.e., accelerating anomalous diffusion. A widely used framework to describe such crossovers in a one-dimensional setting is the bi-fractional diffusion equation of the so-called modified type, involving two time-fractional derivatives defined in the Riemann-Liouville sense. We here generalise this bi-fractional diffusion equation to higher dimensions and derive its multidimensional propagator (Green's function) for the general case when also a space fractional derivative is present, taking into consideration long-ranged jumps (Levy flights). We derive the asymptotic behaviours for this propagator in both the short- and long-time as well the short- and long-distance regimes. Finally, we also calculate the mean squared displacement, skewness and kurtosis in all dimensions, demonstrating that in the general case the non-Gaussian shape of the probability density function changes. KW - multidimensional fractional diffusion equation KW - continuous time random KW - walks KW - crossover anomalous diffusion dynamics KW - non-Gaussian probability KW - density Y1 - 2022 U6 - https://doi.org/10.1088/1751-8121/ac5a90 SN - 1751-8113 SN - 1751-8121 VL - 55 IS - 20 PB - IOP Publ. Ltd. CY - Bristol ER -