Many applications in chemistry, biology, and energy storage/conversion research rely on molecular simulations to provide fundamental insight into structural and transport properties of materials with ...high ionic concentrations. Whether the system is comprised entirely of ions, like ionic liquids, or is a mixture of a polar solvent with a salt, e.g., liquid electrolytes for battery applications, the presence of ions in these materials results in strong local electric fields polarizing solvent molecules and large ions. To predict properties of such systems from molecular simulations often requires either explicit or mean-field inclusion of the influence of polarization on electrostatic interactions. In this manuscript, we review the pros and cons of different treatments of polarization ranging from the mean-field approaches to the most popular explicit polarization models in molecular dynamics simulations of ionic materials. For each method, we discuss their advantages and disadvantages and emphasize key assumptions as well as their adjustable parameters. Strategies for the development of polarizable models are presented with a specific focus on extracting atomic polarizabilities. Finally, we compare simulations using polarizable and nonpolarizable models for several classes of ionic systems, discussing the underlying physics that each approach includes or ignores, implications for implementation and computational efficiency, and the accuracy of properties predicted by these methods compared to experiments.
Molecular ionic liquids are typically characterized by strong electrostatic interactions resulting in a charge ordering and retardation of their translational and rotational behaviour. Unfortunately, ...this effect is often overestimated in classical molecular dynamics simulations. This can be circumvented in a twofold way: the easiest way is to reduce the partial charges of the ions to sub-integer values of ±0.7-0.9 e. The more realistic model is to include polarizable forces, e.g. Drude-oscillators, but it comes along with an increasing computational effort. On the other hand, charge-scaled models are claimed to take an average polarizability into account. But do both models have the same impact on structure and dynamics of molecular ionic liquids? In the present study several molecular dynamics simulations of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate are performed with different levels of polarization as well as with varying charge scaling factors of 0.74 to 0.90. The analysis of the structural and dynamical results are performed in different levels: from the atomic point of view over the molecular level to collective properties determined by the complete sample.
Organic matter (OM) is present in most terrestrial environments and is often found coprecipitated with ferrihydrite (Fh). Sorption or coprecipitation of OM with Fe oxides has been proposed to be an ...important mechanism for long-term C preservation. However, little is known about the impact of coprecipitated OM on reductive dissolution and transformation of Fe(III) (oxyhydr)oxides. Thus, we study the effect of humic acid (HA) coprecipitation on Fh reduction and secondary mineral formation by the dissimilatory Fe(III)-reducing bacterium Shewanella putrefaciens strain CN32. Despite similar crystal structure for all coprecipitates investigated, resembling 2-line Fh, the presence of coprecipitated HA resulted in lower specific surface areas. In terms of reactivity, coprecipitated HA resulted in slower Fh bioreduction rates at low C/Fe ratios (i.e., C/Fe ≤ 0.8), while high C/Fe ratios (i.e., C/Fe ≥ 1.8) enhanced the extent of bioreduction compared to pure Fh. The coprecipitated HA also altered the secondary Fe mineralization pathway by inhibiting goethite formation, reducing the amount of magnetite formation, and increasing the formation of a green rust-like phase. This study indicates that coprecipitated OM may influence the rates, pathway, and mineralogy of biogeochemical Fe cycling and anaerobic Fe respiration within soils.
Prior findings are inconclusive concerning the innovation output of family and non-family SMEs. The study at hand takes one step back and examines the drivers of innovation output. Applying a ...contextualized approach, we use data of 1.870 SMEs located in Germany, arguing that the main characteristic of family SMEs is the unity of ownership and leadership. These specific elements affect both the drivers and the output of innovation leading to a more detailed understanding of family firm innovation. Our results indicate that a long-term perspective positively affects innovation output in small family firms. We also show that family firms are better able to preserve the knowledge of the workforce through lower fluctuation rates which leads to higher levels of innovation output. Finally, the succeeding generations of family firm leaders seem to be more risk averse than the founder generation. As a result, the innovation output continuously decreases from generation to generation.
Prenucleation clusters: In situ synchrotron X‐ray scattering with a one‐second time resolution revealed the occurrence of nano‐sized clusters during the nucleation and early growth of nanocrystals of ...a zeolitic imidazolate framework (ZIF). The complex crystallization process exhibits similarities with crystallization processes of zeolites from solution. Hmim= 2‐methylimidazole.
Different spectroscopy types reveal different aspects of molecular processes in soft matter. In particular, collective observables can provide insights into intermolecular correlations invisible to ...the more popular single-particle methods. In this perspective we feature the dielectric relaxation spectroscopy (DRS) with an emphasis on the proper interpretation of this complex observable aided by computational spectroscopy. While we focus on the history and recent advances of DRS in the fields of biomolecular hydration and nanoconfinement, the discussion transcends this particular field and provides a guide for how collective spectroscopy types supported by computational decomposition can be employed to further our understanding of soft matter phenomena.
The creation of a perfect hollow nanoscopic sphere of metal centers is clearly an unrealizable synthetic challenge. It is, however, an inspirational challenge from the viewpoint of chemical ...architecture and also as finite molecular species may provide unique microscopic insight into the origin and onset of phenomena such as topological spin-frustration effects found in infinite 2D and 3D systems. Herein, we report a series of high-symmetry gadolinium(III) (S = 7/2) polyhedra, Gd20 , Gd32 , Gd50 , and Gd60 , to test an approach based on assembling polymetallic fragments that contain different polygons. Structural analysis reveals that the Gd20 cage resembles a dodecahedron; the vertices of the Gd32 polyhedron exactly reveal symmetry O h ; Gd50 displays an unprecedented polyhedron in which an icosidodecahedron Gd30 core is encapsulated by an outer Gd20 dodecahedral shell with approximate I h symmetry; and the Gd60 shows a truncated octahedron geometry. Experimental and theoretical magnetic studies show that this series produces the expected antiferromagnetic interaction that can be modeled based on classical spins at the Gd sites. From the magnetization analyses, we can roughly correlate the derivative bands to the Gd–O–Gd angles. Such a magneto-structural correlation may be used as “fingerprints” to identify these cages.
Microbial humic substance (HS) reduction and subsequent abiotic electron transfer from reduced HS to poorly soluble Fe(III) (oxyhydr)oxides, a process named electron shuttling, significantly ...increases microbial Fe(III) mineral reduction rates. However, the importance of electron shuttling in nature and notably the electron transfer from HS to biogenic Fe(III) (oxyhydr)oxides have thus far not been determined. In this study, we have quantified the rate and extent of electron transfer from reduced and nonreduced Pahokee Peat humic acids (PPHA) and fresh soil organic matter (SOM) extracts to both synthetic and environmentally relevant biogenic Fe(III) (oxyhydr)oxides. We found that biogenic Fe(III) minerals were reduced faster and to an equal or higher degree than their abiogenic counterparts. Differences were attributed to differences in crystallinity and the association of bacterial biomass with biogenic minerals. Compared to purified PPHA, SOM extract transferred fewer electrons per milligram of carbon and electron transfer was observed only to poorly crystalline ferrihydrite but not to more crystalline goethite. This indicates a difference in redox potential distribution of the redox-active functional groups in extracted SOM relative to the purified PPHA. Our results suggest that HS electron shuttling can also contribute to iron redox processes in environments where biogenic Fe(III) minerals are present.
In this computational study, the collective translational motions of 1-ethyl-3-methylimidazolium triflate, characterized by its current correlation function and its collective dipolar displacement, ...are interpreted in terms of an ion cage around a central ion. Thereby, a coincidence of the relevant time constants is observed. Furthermore, the ion cage is long living and its composition is rather heterogeneous. Besides high numbers of counter ions, several ions of like charge populate the first shell around a central ion. In contrast to the strong influence of the local environment on the collective translational motion, rotations are strictly collective. In other words, a local picture falls short of describing the overall antiparallel alignment of ionic dipoles. A further issue of this work is the interpretation of the initial region of the collective dipolar displacement. It can be related to all collective translational processes showing up in the computational dielectric spectrum. In particular, slow translational processes which are invisible in the current correlation function can be detected. The inclusion of these slow processes allow for an excellent computational reconstruction of the experimental spectrum of the generalized dielectric constant.
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