03 Fakultät Chemie
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/4
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Item Open Access 3D sub-nanometer analysis of glucose in an aqueous solution by cryo-atom probe tomography(2021) Schwarz, T. M.; Dietrich, C. A.; Ott, J.; Weikum, E. M.; Lawitzki, R.; Solodenko, H.; Hadjixenophontos, E.; Gault, B.; Kästner, J.; Schmitz, G.; Stender, P.Atom Probe Tomography (APT) is currently a well-established technique to analyse the composition of solid materials including metals, semiconductors and ceramics with up to near-atomic resolution. Using an aqueous glucose solution, we now extended the technique to frozen solutions. While the mass signals of the common glucose fragments CxHy and CxOyHz overlap with (H2O)nH from water, we achieved stoichiometrically correct values via signal deconvolution. Density functional theory (DFT) calculations were performed to investigate the stability of the detected pyranose fragments. This paper demonstrates APT’s capabilities to achieve sub-nanometre resolution in tracing whole glucose molecules in a frozen solution by using cryogenic workflows. We use a solution of defined concentration to investigate the chemical resolution capabilities as a step toward the measurement of biological molecules. Due to the evaporation of nearly intact glucose molecules, their position within the measured 3D volume of the solution can be determined with sub-nanometre resolution. Our analyses take analytical techniques to a new level, since chemical characterization methods for cryogenically-frozen solutions or biological materials are limited.Item Open Access Ab initio based method to study structural phase transitions in dynamically unstable crystals, with new insights on the β to ω transformation in titanium(2019) Korbmacher, Dominique; Glensk, Albert; Duff, Andrew Ian; Finnis, Michael W.; Grabowski, Blazej; Neugebauer, JörgWe present an approach that enables an efficient and accurate study of dynamically unstable crystals over the full temperature range. The approach is based on an interatomic potential fitted to ab initio molecular dynamics energies for both the high- and low-temperature stable phases. We verify by comparison to explicit ab initio simulations that such a bespoke potential, for which we use here the functional form of the embedded atom method, provides accurate transformation temperatures and atomistic features of the transformation. The accuracy of the potential makes it an ideal tool to study the important impact of finite size and finite time effects. We apply our approach to the dynamically unstable β (bcc) titanium phase and study in detail the transformation to the low-temperature stable hexagonal ω phase. We find a large set of previously unreported linear-chain disordered (LCD) structures made up of three types of [111]β linear-chain defects that exhibit randomly disordered arrangements in the (111)β plane.Item Open Access Ab initio machine-learning unveils strong anharmonicity in non-Arrhenius self-diffusion of tungsten(2025) Zhang, Xi; Divinski, Sergiy V.; Grabowski, BlazejThe knowledge of diffusion mechanisms in materials is crucial for predicting their high-temperature performance and stability, yet accurately capturing the underlying physics like thermal effects remains challenging. In particular, the origin of the experimentally observed non-Arrhenius diffusion behavior has remained elusive, largely due to the lack of effective computational tools. Here we propose an efficient ab initio framework to compute the Gibbs energy of the transition state in vacancy-mediated diffusion including the relevant thermal excitations at the density-functional-theory level. With the aid of a bespoke machine-learning interatomic potential, the temperature-dependent vacancy formation and migration Gibbs energies of the prototype system body-centered cubic (BCC) tungsten are shown to be strongly affected by anharmonicity. This finding explains the physical origin of the experimentally observed non-Arrhenius behavior of tungsten self-diffusion. A remarkable agreement between the calculated and experimental temperature-dependent self-diffusivity and, in particular, its curvature is revealed. The proposed computational framework is robust and broadly applicable, as evidenced by first tests for a hexagonal close-packed (HCP) multicomponent high-entropy alloy. The successful applications underscore the attainability of an accurate ab initio diffusion database.Item Open Access Ab initio modelling of solute segregation energies to a general grain boundary(2017) Huber, Liam; Grabowski, Blazej; Militzer, Matthias; Neugebauer, Jörg; Rottler, JörgWe apply a quantum mechanical/molecular mechanical (QM/MM) multiscale approach to calculate the segregation energies of Mg and Pb to two kinds of grain boundaries in Al. The first boundary, a symmetric (310)[001] ∑5 tilt boundary, is also tractable using traditional QM calculations, and serves as a validation for the QM/MM method. The second boundary is a general, low-symmetry tilt boundary that is completely inaccessible to pure QM calculations. QM/MM results for both of these boundaries are used to evaluate the accuracy of empirical (EAM) potentials for the Al-Mg and Al-Pb alloy systems. Based on these results we develop a physical model for the segregation energy based on elastic interaction and bond breaking terms. Both MM calculations with the EAM potentials and the model work quantitatively well for describing Mg-GB interaction across a wide range of local environments. For Pb, MM performance is weaker and the model provides only qualitative insight, demonstrating the utility of a QM/MM approach.Item Open Access Ab initio phase stabilities and mechanical properties of multicomponent alloys: a comprehensive review for high entropy alloys and compositionally complex alloys(2019) Ikeda, Yuji; Grabowski, Blazej; Körmann, FritzMulticomponent alloys with multiple principal elements including high entropy alloys (HEAs) and compositionally complex alloys (CCAs) are attracting rapidly growing attention. The endless possibilities to explore new alloys and the hope for better combinations of materials properties have stimulated a remarkable number of research works in the last years. Most of these works have been based on experimental approaches, but ab initio calculations have emerged as a powerful approach that complements experiment and serves as a predictive tool for the identification and characterization of promising alloys. The theoretical ab initio modeling of phase stabilities and mechanical properties of multi-principal element alloys by means of density functional theory (DFT) is reviewed. A general thermodynamic framework is laid down that provides a bridge between the quantities accessible with DFT and the targeted thermodynamic and mechanical properties. It is shown how chemical disorder and various finite-temperature excitations can be modeled with DFT. Different concepts to study crystal and alloy phase stabilities, the impact of lattice distortions (a core effect of HEAs), magnetic transitions, and chemical short-range order are discussed along with specific examples. Strategies to study elastic properties, stacking fault energies, and their dependence on, e.g., temperature or alloy composition are illustrated. Finally, we provide an extensive compilation of multi-principal element alloys and various material properties studied with DFT so far (a set of over 500 alloy-property combinations).Item Open Access Ab initio simulations of the surface free energy of TiN(001)(2021) Forslund, Axel; Zhang, Xi; Grabowski, Blazej; Shapeev, Alexander V.; Ruban, Andrei V.The temperature dependence of the surface free energy of the industrially important TiN(001) system has been investigated by means of an extended two-stage upsampled thermodynamic integration using Langevin dynamics (TU-TILD) methodology, to include the fully anharmonic vibrational contribution, as obtained from ab initio molecular dynamics (AIMD). Inclusion of the fully anharmonic behavior is crucial, since the standard low-temperature quasiharmonic approximation exhibits a severe divergence in the surface free energy due to a high-temperature dynamical instability. The anharmonic vibrations compensate for the quasiharmonic divergence and lead to a modest overall temperature effect on the TiN(001) surface free energy, changing it from around 78 meV Å-2 at 0 K to 73 meV Å-2 at 3000 K. The statistical convergence of the molecular dynamics is facilitated by the use of machine-learning potentials, specifically moment tensor potentials, fitted for TiN(001) at finite temperature. The surface free energy obtained directly from the fitted machine-learning potentials is close to that obtained from the full AIMD simulations.Item Open Access Ab initio surface free energies of tungsten with full account of thermal excitations(2022) Forslund, Axel; Ruban, AndreiThe surface free energies of seven different facets of tungsten (W) are obtained up to the melting point with full account of all the relevant thermal excitations; in particular, thermal atomic vibrations, electronic excitations, and their mutual coupling. The latter is done using ab initio molecular dynamics simulations coupled with the thermodynamic integration technique. In this way, the calculations contain almost no error but the one related to the used exchange-correlation functional, which makes the results truly first principles. The obtained results are compared with previous quasiharmonic calculations for the surface free energies of W and experimental data. The anharmonic contribution is, as expected, important for open surfaces at high temperatures, which leads to a temperature dependence of the surface energy anisotropy. The calculated Wulff shapes and surface energies are in excellent agreement with experimental data close to the melting point, where the crystalline structure of the surface layers is destroyed by a dramatic mobility of the atoms there.Item Open Access Accelerating ab initio melting property calculations with machine learning : application to the high entropy alloy TaVCrW(2024) Zhu, Li-Fang; Körmann, Fritz; Chen, Qing; Selleby, Malin; Neugebauer, Jörg; Grabowski, BlazejMelting properties are critical for designing novel materials, especially for discovering high-performance, high-melting refractory materials. Experimental measurements of these properties are extremely challenging due to their high melting temperatures. Complementary theoretical predictions are, therefore, indispensable. One of the most accurate approaches for this purpose is the ab initio free-energy approach based on density functional theory (DFT). However, it generally involves expensive thermodynamic integration using ab initio molecular dynamic simulations. The high computational cost makes high-throughput calculations infeasible. Here, we propose a highly efficient DFT-based method aided by a specially designed machine learning potential. As the machine learning potential can closely reproduce the ab initio phase-space distribution, even for multi-component alloys, the costly thermodynamic integration can be fully substituted with more efficient free energy perturbation calculations. The method achieves overall savings of computational resources by 80% compared to current alternatives. We apply the method to the high-entropy alloy TaVCrW and calculate its melting properties, including the melting temperature, entropy and enthalpy of fusion, and volume change at the melting point. Additionally, the heat capacities of solid and liquid TaVCrW are calculated. The results agree reasonably with the CALPHAD extrapolated values.Item Open Access Accurate electronic free energies of the 3d, 4d, and 5d transition metals at high temperatures(2017) Zhang, Xi; Grabowski, Blazej; Körmann, Fritz; Freysoldt, Christoph; Neugebauer, JörgFree energies of bulk materials are nowadays routinely computed by density functional theory. In particular for metals, electronic excitations can significantly contribute to the free energy. For an ideal static lattice, this contribution can be obtained at low computational cost, e.g., from the electronic density of states derived at T = 0 K or by utilizing the Sommerfeld approximation. The error introduced by these approximations at elevated temperatures is rarely known. The error arising from the ideal lattice approximation is likewise unexplored but computationally much more challenging to overcome. In order to shed light on these issues we have computed the electronic free energies for all 3d, 4d, and 5d transition elements on the ideal lattices of the bcc, fcc, and hcp structures using finite-temperature density-functional theory. For a subset of elements we have explored the impact of explicit thermal vibrations on the electronic free energies by using ab initio molecular dynamics simulations. We provide an analysis of the observed chemical trends in terms of the electronic density of states and the canonical d band model and quantify the errors in the approximate methods. The electronic contribution to the heat capacities and the corresponding errors due to the different approximations are studied as well.Item Open Access Activation and fixation of atmospheric CO2 through a 1,2,3‐triazole‐based mesoionic carbene-borane adduct(2025) Neubrand, Maren; Stubbe, Jessica; Rudolf, Richard; Walter, Robert R. M.; Nößler, Maite; Sarkar, BiprajitCapturing atmospheric CO2 and converting it to valuable chemicals are important goals in contemporary science. We present here a simple, transition metal‐free triazolylidene–borane adduct that can capture atmospheric CO2 and convert it to formate. Several key intermediates were isolated and characterized by a combination of multinuclear NMR spectroscopy, IR spectroscopy and single crystal X‐ray diffraction. A first closed cycle for the conversion of CO2 to formic acid by using the aforementioned triazolylidene–borane compound is presented as well.Item Open Access Activation of aromatic C-F bonds by a N‐heterocyclic olefin (NHO)(2020) Mandal, Debdeep; Chandra, Shubhadeep; Neuman, Nicolás I.; Mahata, Alok; Sarkar, Arighna; Kundu, Abhinanda; Anga, Srinivas; Rawat, Hemant; Schulzke, Carola; Mote, Kaustubh R.; Sarkar, Biprajit; Chandrasekhar, Vadapalli; Jana, AnukulA N‐heterocyclic olefin (NHO), a terminal alkene selectively activates aromatic C-F bonds without the need of any additional catalyst. As a result, a straightforward methodology was developed for the formation of different fluoroaryl‐substituted alkenes in which the central carbon-carbon double bond is in a twisted geometry.Item Open Access An acyclic diaminocarbene complex of platinum formed by desulfurization of 1,3‐bis(3‐methylpyridin‐2‐yl)thiourea(2021) Bulak, Ece; Dogan, Ilknur; Varnali, Tereza; Schwederski, Brigitte; Gunal, Sule Erol; Lönnecke, Peter; Bubrin, Martina; Kaim, WolfgangThe reaction of the ambidentate ligand 1,3‐bis(3‐methylpyridin‐2‐yl)thiourea (1) with [PtCl2(dmso)2] in dichloromethane led to formation of a poorly soluble compound 2, characterized as a conventional chelate complex [PtCl2(1)]=2. Reaction in methanol resulted in desulfurization to produce a fluorescing cationic diaminocarbene-platinum(II) complex 3, the structure of which was elucidated by X‐ray crystallography, mass spectrometry and NMR. Experimental findings were supported by DFT calculations.Item Open Access Adducts of diaminophosphines with organoboranes(2022) Dunaj, Tobias; Feil, Christoph M.; Nieger, Martin; Gudat, DietrichReactions of chlorodiaminophosphines (R2N)2PCl (R=Et, iPr) with organoborohydrides M[BR′nH4‐n] (M=Na, Li; n=1-3; R′=alkyl, Ph, CN) proceed via H/Cl metathesis to furnish secondary phosphines and boranes which may either combine to afford isolable donor‐acceptor adducts (R2N)2P(H)-BR′nH3‐n, coexist without any sign of mutual interaction, or give rise to mixtures comprising both a labile phosphine borane and its constituents in a temperature dependent equilibrium. Stable phosphine complexes of BH2CN and BH2Ph react with KN(SiMe3)2 under PH‐bond metalation to afford spectroscopically detectable diaminophosphide boranes whose usability as nucleophilic building blocks is illustrated by trapping one specimen in a PC‐bond formation reaction with an alkyl halide. The selectivity of the individual H/Cl‐metathesis and electrophilic substitution steps as well as the thermal stability of the various reaction products depend subtly on the Lewis acidity of the borane fragment and on steric factors. Several complexes of (iPr2N)‐substituted phosphines with cyano‐ and phenylborane were characterized by single‐crystal XRD.Item Open Access Adjustable polystyrene nanoparticle templates for the production of mesoporous foams and ZnO inverse opals(2020) Abitaev, Karina; Qawasmi, Yaseen; Atanasova, Petia; Dargel, Carina; Bill, Joachim; Hellweg, Thomas; Sottmann, ThomasThe manifold applications of porous materials, such as in storage, separation, and catalysis, have led to an enormous interest in their cost-efficient preparation. A promising strategy to obtain porous materials with adjustable pore size and morphology is to use templates exhibiting the appropriate nanostructure. In this study, close-packed polystyrene (PS) nanoparticles, synthesized by emulsion polymerization, were used to produce porous PS and ZnO inverse opals. The size and distribution of the polystyrene nanoparticles, characterized by dynamic light scattering (DLS), small-angle neutron scattering (SANS), and scanning electron microscopy (SEM), were controlled via the concentration of sodium dodecyl sulfate (SDS). Systematic measurements of the water/styrene-interfacial tension show that the critical micelle concentration (CMC) of the ternary water–styrene–SDS system, which determines whether monodisperse or polydisperse PS particles are obtained, is considerably lower than that of the binary water–SDS system. The assemblies of close-packed PS nanoparticles obtained via drying were then studied by small-angle X-ray scattering (SAXS) and SEM. Both techniques prove that PS nanoparticles synthesized above the CMC result in a significantly unordered but denser packing of the particles. The polystyrene particles were subsequently used to produce porous polystyrene and ZnO inverse opals. While the former consists of micrometer-sized spherical pores surrounded by extended open-cellular regions of mesopores (Rpore ≈ 25 nm), the latter are made of ZnO-nanoparticles forming a structure of well-aligned interconnected pores.Item Open Access Aging‐driven composition and distribution changes of electrolyte and graphite anode in 18650‐type Li‐ion batteries(2022) Petz, Dominik; Baran, Volodymyr; Peschel, Christoph; Winter, Martin; Nowak, Sascha; Hofmann, Michael; Kostecki, Robert; Niewa, Rainer; Bauer, Michael; Müller‐Buschbaum, Peter; Senyshyn, AnatoliyA series of low‐temperature studies on LiNi0.80Co0.15Al0.05O2 18650‐type batteries of high‐energy type with different stabilized states of fatigue is carried out using spatially resolved neutron powder diffraction, infrared/thermal imaging, and quasi‐adiabatic calorimetry. In‐plane distribution of lithium in the graphite anode and frozen electrolyte in fully charged state is determined non‐destructively with neutron diffraction and correlated to the introduced state of fatigue. An independent electrolyte characterization is performed via calorimetry studies on variously aged 18650‐type lithium‐ion batteries, where the shape of the thermodynamic signal is evolving with the state of fatigue of the cells. Analyzing the liquid electrolyte extracted/harvested from the studied cells reveals the decomposition of conducting salt to be the main driving factor for fatigue in the electrolyte degradation.Item Open Access Aktivierte Modifikation der Träger‐Metall‐Wechselwirkungen als Schlüssel für hochaktive Ru/γ‐Al2O3‐Katalysatoren für die COx‐Methanisierung(2020) Chen, Shilong; Abdel‐Mageed, Ali M.; Dyballa, Michael; Parlinska‐Wojtan, Magdalena; Bansmann, Joachim; Pollastri, Simone; Olivi, Luca; Aquilanti, Giuliana; Behm, R. JürgenRu/Al2O3 ist ein außerordentlich stabiler, aber weniger aktiver Katalysator für Methanisierungs-Reaktionen. Hier berichten wir über einen neuartigen Ansatz, mit dem die Aktivität dieser Katalysatoren bei der Methanisierung von CO2 in CO2/H2-Gemischen erheblich gesteigert werden kann. Hochaktive und -stabile Ru/γ-Al2O3-Katalysatoren wurden über eine Hochtemperatur-Behandlung im reduktiven Reaktionsgasgemisch erhalten. Operando/In-situ-Spektroskopie und Rastertransmissionselektronenmikroskopie (STEM)-Abbildungen zeigen, dass die deutlich erhöhte Aktivität für die Methanisierung von CO bzw. CO2 mit einer Abflachung der Ru-Nanopartikel und der Bildung von stark basischen Plätzen auf dem hydroxylierten Aluminiumoxid einhergeht. Die erhöhte Aktivität der Katalysatoren um Faktoren von 5 (CO) bzw. 14 (CO2) führen wir auf eine aktivierte Modifikation der Träger-Metall-Wechselwirkungen zurück, die durch eine reaktive Modifizierung der Al2O3-Oberfläche im Reaktionsgas und eine erhöhte thermische Mobilität der Ru-Nanopartikel verursacht wird.Item Open Access Aligning and observing the liquid crystal director in 3D using small magnetic fields and a wedge‐cell(2025) Gulati, Lovish; Sánchez‐Somolinos, Carlos; Giesselmann, Frank; Fischer, PeerThe mechanical and optical properties of liquid crystalline materials are largely dependent on the director profile. More complex soft robotic functions and programmed optical properties require spatially varying director profiles, ideally in 3D. However, it is challenging to achieve arbitrary director orientation with most established alignment techniques, as one needs to overcome surface interactions, use high electric or magnetic field strengths and temperatures. Another experimental difficulty is that there is a lack of suitable techniques that can be used to characterize the director in 3D. Here, this study first shows that the addition of 5CB to reactive mesogens permits cross‐linked liquid crystalline materials to be fabricated with a spatially varying 3D director profile using weak magnetic fields (0.13 T). This study also shows, how these can be characterized with an optical technique that uses a wedge cell to visualize the programmed 3D director profile. Interestingly, the method also permits the real‐time observation of the director. This work shows that it is possible to precisely control the director in 3D with low magnetic fields and that the dynamics can be directly observed, which facilitates potential applications of soft liquid crystalline (LC) gels and potentially also elastomers.Item Open Access Alkaline metal intercalates of VSe2 by electrochemical intercalation(2023) Kannen, Bastian; Rasche, BertoldWe report on the series of the alkali metal intercalates of VSe2 synthesised by electrochemical means in an aqueous environment. For all alkali metals we find water‐conintercalated structures (stage I and stage II), of which only the sodium structure had been reported so far. The new structures are analyzed by powder X‐ray diffraction and Rietveld refinement. Their (meta‐)stability is investigated in terms of the open circuit potential, revealing the sensitivity towards oxygen. Except for the lithium intercalate these structures transform into water‐free alkali metal intercalates under vacuum. In addition, scanning electron microscopy reveals the impact of different electrochemical intercalation techniques yielding different intercalation rates. This paves the way for future single crystal investigations.Item Open Access Amphotropic azobenzene derivatives with oligooxyethylene and glycerol based polar groups(2015) Tan, Xiaoping; Zhang, Ruilin; Guo, Chunxiang; Cheng, Xiaohong; Gao, Hongfei; Liu, Feng; Bruckner, Johanna R.; Gießelmann, Frank; Prehm, Marko; Tschierske, CarstenA series of amphiphilic azobenzenes with one to three lipophilic alkyl chains at one end and polar groups with oligooxyethylene (EO) and racemic 3-glyceryl units at the opposite end was synthesized and their thermotropic and lyotropic liquid crystalline self-assemblies were studied by POM, DSC and XRD. Tilted and non-tilted lamellar phases with interdigitated double layer structures (SmCd and SmAd, respectively) were found for the compounds with a single alkyl chain, whereas hexagonal columnar phases were formed by the compounds with two or three alkyl chains. The effect of protic solvents, like formamide, ethylene glycol and water, was investigated for representative examples. For the compounds with the single chain, induction and stabilization of SmA phases were observed, though broad regions of lyotropic SmC phases were retained in most cases. Depending on the structure of the polar group, the hexagonal columnar phases were either removed or drastically stabilized by the solvents. Photoisomerisation of an azobenzene chromophore was also studied.Item Open Access Analysis of 3760 hematologic malignancies reveals rare transcriptomic aberrations of driver genes(2024) Cao, Xueqi; Huber, Sandra; Ahari, Ata Jadid; Traube, Franziska R.; Seifert, Marc; Oakes, Christopher C.; Secheyko, Polina; Vilov, Sergey; Scheller, Ines F.; Wagner, Nils; Yépez, Vicente A.; Blombery, Piers; Haferlach, Torsten; Heinig, Matthias; Wachutka, Leonhard; Hutter, Stephan; Gagneur, JulienBackground. Rare oncogenic driver events, particularly affecting the expression or splicing of driver genes, are suspected to substantially contribute to the large heterogeneity of hematologic malignancies. However, their identification remains challenging. Methods. To address this issue, we generated the largest dataset to date of matched whole genome sequencing and total RNA sequencing of hematologic malignancies from 3760 patients spanning 24 disease entities. Taking advantage of our dataset size, we focused on discovering rare regulatory aberrations. Therefore, we called expression and splicing outliers using an extension of the workflow DROP (Detection of RNA Outliers Pipeline) and AbSplice, a variant effect predictor that identifies genetic variants causing aberrant splicing. We next trained a machine learning model integrating these results to prioritize new candidate disease-specific driver genes. Results. We found a median of seven expression outlier genes, two splicing outlier genes, and two rare splice-affecting variants per sample. Each category showed significant enrichment for already well-characterized driver genes, with odds ratios exceeding three among genes called in more than five samples. On held-out data, our integrative modeling significantly outperformed modeling based solely on genomic data and revealed promising novel candidate driver genes. Remarkably, we found a truncated form of the low density lipoprotein receptor LRP1B transcript to be aberrantly overexpressed in about half of hairy cell leukemia variant (HCL-V) samples and, to a lesser extent, in closely related B-cell neoplasms. This observation, which was confirmed in an independent cohort, suggests LRP1B as a novel marker for a HCL-V subclass and a yet unreported functional role of LRP1B within these rare entities. Conclusions. Altogether, our census of expression and splicing outliers for 24 hematologic malignancy entities and the companion computational workflow constitute unique resources to deepen our understanding of rare oncogenic events in hematologic cancers.