TY - JOUR A1 - Utecht, Manuel Martin A1 - Klamroth, Tillmann T1 - Local resonances in STM manipulation of chlorobenzene on Si(111)-7x7 BT - performance of different cluster models and density functionals JF - Molecular physics N2 - Hot localised charge carriers on the Si(111)-7x7 surface are modelled by small charged clusters. Such resonances induce non-local desorption, i.e. more than 10 nm away from the injection site, of chlorobenzene in scanning tunnelling microscope experiments. We used such a cluster model to characterise resonance localisation and vibrational activation for positive and negative resonances recently. In this work, we investigate to which extent the model depends on details of the used cluster or quantum chemistry methods and try to identify the smallest possible cluster suitable for a description of the neutral surface and the ion resonances. Furthermore, a detailed analysis for different chemisorption orientations is performed. While some properties, as estimates of the resonance energy or absolute values for atomic changes, show such a dependency, the main findings are very robust with respect to changes in the model and/or the chemisorption geometry. [GRAPHICS] . KW - DFT KW - cluster model KW - charge localisation KW - STM Y1 - 2018 U6 - https://doi.org/10.1080/00268976.2018.1442939 SN - 0026-8976 SN - 1362-3028 VL - 116 IS - 13 SP - 1687 EP - 1696 PB - Routledge, Taylor & Francis Group CY - Abingdon ER - TY - GEN A1 - Utecht, Manuel Martin A1 - Klamroth, Tillmann T1 - Local resonances in STM manipulation of chlorobenzene on Si(111)-7×7 BT - performance of different cluster models and density functionals T2 - Molecular Physics N2 - Hot localised charge carriers on the Si(111)-7×7 surface are modelled by small charged clusters. Such resonances induce non-local desorption, i.e. more than 10 nm away from the injection site, of chlorobenzene in scanning tunnelling microscope experiments. We used such a cluster model to characterise resonance localisation and vibrational activation for positive and negative resonances recently. In this work, we investigate to which extent the model depends on details of the used cluster or quantum chemistry methods and try to identify the smallest possible cluster suitable for a description of the neutral surface and the ion resonances. Furthermore, a detailed analysis for different chemisorption orientations is performed. While some properties, as estimates of the resonance energy or absolute values for atomic changes, show such a dependency, the main findings are very robust with respect to changes in the model and/or the chemisorption geometry. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 463 KW - DFT KW - cluster model KW - charge localisation KW - STM Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-412970 ER - TY - JOUR A1 - Taran, Michail N. A1 - Nunez Valdez, Maribel A1 - Efthimiopoulos, Ilias A1 - Müller, J. A1 - Reichmann, Hans-Josef A1 - Wilke, Max A1 - Koch-Müller, Monika T1 - Spectroscopic and ab initio studies of the pressure-induced Fe2+ high-spin-to-low-spin electronic transition in natural triphylite-lithiophilite JF - Physics and Chemistry of Minerals N2 - Using optical absorption and Raman spectroscopic measurements, in conjunction with the first-principles calculations, a pressure-induced high-spin (HS)-to-low-spin (LS) state electronic transition of Fe2+ (M2-octahedral site) was resolved around 76-80GPa in a natural triphylite-lithiophilite sample with chemical composition (LiFe0.7082+Mn0.292PO4)-Li-M1-Fe-M2 (theoretical composition (LiFe0.52+Mn0.5PO4)-Li-M1-Fe-M2). The optical absorption spectra at ambient conditions consist of a broad doublet band with two constituents (1) (similar to 9330cm(-1)) and (2) (similar to 7110cm(-1)), resulting from the electronic spin-allowed transition (T2gEg)-T-5-E-5 of octahedral (HSFe2+)-Fe-M2. Both (1) and (2) bands shift non-linearly with pressure to higher energies up to similar to 55GPa. In the optical absorption spectrum measured at similar to 81GPa, the aforementioned HS-related bands disappear, whereas a new broadband with an intensity maximum close to 16,360cm(-1) appears, superimposed on the tail of the high-energy ligand-to-metal O2-Fe2+ charge-transfer absorption edge. We assign this new band to the electronic spin-allowed dd-transition (1)A(1g)(1)T(1g) of LS Fe2+ in octahedral coordination. The high-pressure Raman spectra evidence the Fe2+ HS-to-LS transition mainly from the abrupt shift of the P-O symmetric stretching modes to lower frequencies at similar to 76GPa, the highest pressure achieved in the Raman spectroscopic experiments. Calculations indicated that the presence of Mn-M2(2+) simply shifts the isostructural HS-to-LS transition to higher pressures compared to the triphylite Fe-M2(2+) end-member, in qualitative agreement with our experimental observations. KW - Phosphates KW - Triphylite KW - Raman KW - Infrared KW - Optical absorption spectroscopy KW - High pressure KW - Spin transition KW - DFT Y1 - 2019 U6 - https://doi.org/10.1007/s00269-018-1001-y SN - 0342-1791 SN - 1432-2021 VL - 46 IS - 3 SP - 245 EP - 258 PB - Springer CY - New York ER - TY - JOUR A1 - Spiekermann, Georg A1 - Wilke, Max A1 - Jahn, Sandro T1 - Structural and dynamical properties of supercritical H2O-SiO2 fluids studied by ab initio molecular dynamics JF - Chemical geology : official journal of the European Association for Geochemistry N2 - In this study we report the structure of supercritical H2O-SiO2 fluid composed of 50 mol% H2O and 50 mol% SiO2 at 3000 K and 2400 K. investigated by means of ab initio molecular dynamics of models comprising 192 and 96 atoms. The density is set constant to 138 g/cm(3), which yields a pressure of 4.3 GPa at 3000 K and 3.6 GPa at 2400 K. Throughout the trajec[ories, water molecules are formed and dissociated via the network modifying reaction 2 SiOH = SiOSi + H2O The calculation of the reaction constant K- [OH](2)/[H2O][O2-] is carried out on the basis of the experimentally relevant Q ' species notation and agrees well with an extrapolation of experimental data to 3000 K. After quench from 3000 K to 2400 K, the degree of polymerization of the silicate network in the 192-atom models increases noticeably within several tens of picoseconds, accompanied by release of molecular H2O. An unexpected opposite trend is observed in smaller 96-atom models, due to a finite size effect, as several uncorrelated models of 192 and 96 atoms indicate. The temperature-dependent slowing down of the H2O-silica interaction dynamics is described on the basis of the bond autocorrelation function. (C) 2016 Elsevier B.V. All rights reserved. KW - Fluid KW - SiO2-H2O KW - SiO(2)Molecular dynamics KW - Polymerization KW - DFT Y1 - 2016 U6 - https://doi.org/10.1016/j.chemgeo.2016.01.010 SN - 0009-2541 SN - 1878-5999 VL - 426 SP - 85 EP - 94 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Shainyan, Bagrat A. A1 - Suslova, Elena N. A1 - Tran Dinh Phien, A1 - Shlykov, Sergey A. A1 - Kleinpeter, Erich T1 - Synthesis, conformational preferences in gas and solution, and molecular gear rotation in 1-(dimethylamino)-1-phenyl-1-silacyclohexane by gas phase electron diffraction (GED), LT NMR and theoretical calculations JF - Tetrahedron N2 - 1-(Dimethylamino)-1-phenyl-1-silacyclohexane 1, was synthesized, and its molecular structure and conformational properties studied by gas-phase electron diffraction (GED), low temperature C-13 NMR spectroscopy and quantum-chemical calculations. The predominance of the 1-Ph-ax conformer (1-Ph-eq:1-Ph-ax ratio of 20:80%, Delta G degrees (317 K) = -0.87 kcal/mol) in the gas phase is close to the theoretically estimated conformational equilibrium. In solution, low temperature NMR spectroscopy showed analyzable decoalescence of C-ipso and C(1,5) carbon signals in C-13 NMR spectra at 103 K. Opposite to the gas state in the freon solution employed (CD2Cl2/CHFCl2/CHFCl2 = 1:1:3), which is still liquid at 100 K, the 1-Ph-eq conformer was found to be the preferred one [(1-Ph-eq: 1-Ph-ax = 77%: 23%, K = 77/23 = 2.8; -Delta G degrees = -RT In K (at 103 K) = 0.44 +/- 0.1 kcal/mol]. When comparing 1 with 1-phenyl-1-(X)silacylohexanes (X = H, Me, OMe, F, Cl), studied so far, the trend of predominance of the Ph-ax conformer in the gas phase and of the Ph-eq conformer in solution is confirmed. KW - 1-(Dimethylamino)-1-phenyl-1-silacyclohexane KW - Conformational analysis KW - Gas phase electron diffraction KW - Low-temperature d-NMR KW - DFT KW - MP2 KW - M062X/6-311G** calculations Y1 - 2018 U6 - https://doi.org/10.1016/j.tet.2018.06.023 SN - 0040-4020 VL - 74 IS - 32 SP - 4299 EP - 4307 PB - Elsevier CY - Oxford ER - TY - THES A1 - Rietze, Clemens T1 - Optimierung und Analyse von molekularen Schaltern in komplexen Umgebungen: thermische Stabilität, Auslesbarkeit und Schaltbarkeit T1 - Optimization and analysis of molecular switches in complex environments: thermal stability, selectability and switchability N2 - Seit Jahrzehnten stellen die molekularen Schalter ein wachsendes Forschungsgebiet dar. Im Rahmen dieser Dissertation stand die Verbesserung der thermischen Stabilität, der Auslesbarkeit und Schaltbarkeit dieser molekularen Schalter in komplexen Umgebungen mithilfe computergestützter Chemie im Vordergrund. Im ersten Projekt wurde die Kinetik der thermischen E → Z-Isomerisierung und die damit verbundene thermische Stabilität eines Azobenzol-Derivats untersucht. Dafür wurde Dichtefunktionaltheorie (DFT) in Verbindung mit der Eyring-Theorie des Übergangszustandes (TST) angewendet. Das Azobenzol-Derivat diente als vereinfachtes Modell für das Schalten in einer komplexen Umgebung (hier in metallorganischen Gerüsten). Es wurden thermodynamische und kinetische Größen unter verschiedenen Einflüssen berechnet, wobei gute Übereinstimmungen mit dem Experiment gefunden wurden. Die hier verwendete Methode stellte einen geeigneten Ansatz dar, um diese Größen mit angemessener Genauigkeit vorherzusagen. Im zweiten Projekt wurde die Auslesbarkeit der Schaltzustände in Form des nichtlinearen optischen (NLO) Kontrastes für die Molekülklasse der Fulgimide untersucht. Die dafür benötigten dynamischen Hyperpolarisierbarkeiten unter Berücksichtigung der Elektronenkorrelation wurden mittels einer etablierten Skalierungsmethode berechnet. Es wurden verschiedene Fulgimide analysiert, wobei viele experimentelle Befunde bestätigt werden konnten. Darüber hinaus legte die theoretische Vorhersage für ein weiteres System nahe, dass insbesondere die Erweiterung des π-Elektronensystems ein vielversprechender Ansatz zur Verbesserung von NLO-Kontrasten darstellt. Die Fulgimide verfügen somit über nützliche Eigenschaften, sodass diese in Zukunft als Bauelemente in photonischen und optoelektronischen Bereichen Anwendungen finden könnten. Im dritten Projekt wurde die E → Z-Isomerisierung auf ein quantenmechanisch (QM) behandeltes Dimer mit molekularmechanischer (MM) Umgebung und zwei Fluorazobenzol-Monomeren durch Moleküldynamik simuliert. Dadurch wurde die Schaltbarkeit in komplexer Umgebung (hier selbstorgansierte Einzelschichten = SAMs) bzw. von Azobenzolderivaten analysiert. Mit dem QM/MM Modell wurden sowohl Van-der-Waals-Interaktionen mit der Umgebung als auch elektronische Kopplung (nur zwischen QM-Molekülen) berücksichtigt. Dabei wurden systematische Untersuchungen zur Packungsdichte durchgeführt. Es zeigte sich, dass bereits bei einem Molekülabstand von 4.5 Å die Quantenausbeute (prozentuale Anzahl erfolgreicher Schaltprozesse) des Monomers erreicht wird. Die größten Quantenausbeuten wurden für die beiden untersuchten Fluorazobenzole erzielt. Es wurden die Effekte des Molekülabstandes und der Einfluss von Fluorsubstituenten auf die Dynamik eingehend untersucht, sodass der Weg für darauf aufbauende Studien geebnet ist. N2 - For decades, molecular switches have represented a growing field of research. In this dissertation, the focus was on improving the thermal stability, selectability and switchability of these molecular switches in complex environments using computer-aided chemistry. In the first project, the kinetics of thermal E → Z isomerization and the associated thermal stability of an azobenzene derivative were investigated. For this purpose, density functional theory (DFT) in combination with the Eyring theory of transition state (TST) was applied. The azobenzene derivative served as a simplified model for switching in a complex environment (here in metalorganic frameworks). Thermodynamic and kinetic quantities under different influences were calculated, and good agreement with the experiment was found. The method used here represented a suitable approach to predict these quantities with reasonable accuracy. In the second project, the selectability of the switching states in the form of nonlinear optical (NLO) contrast for the molecular class of fulgimides was investigated. The dynamic hyperpolarizabilities required for this, taking into account electron correlation, were calculated using an established scaling method. Different fulgimides were analyzed and many experimental findings were confirmed. Furthermore, the theoretical prediction for another system suggested that especially the extension of the π-electron system is a promising approach to improve NLO contrasts. The fulgimides thus possess useful properties, so that they could find future applications as devices in photonic and optoelectronic fields. In the third project, the E → Z-isomerization on a quantum mechanical (QM) treated dimer with molecular mechanical (MM) environment and two fluorazobenzene monomers was simulated by molecular dynamics. Thereby the switchability in complex environment (here self-assembled monolayers = SAMs) respectively of azobenzene derivatives was analyzed. With the QM/MM model both Van-der-Waals-interactions with the environment and electronic coupling (only between QM molecules) were considered. Systematic investigations on packing density were performed. It was shown that already at a molecule distance of 4.5 Å the quantum yield (percentage number of successful switching processes) of the monomer is reached. The highest quantum yields were achieved for the two fluorazobenzenes investigated. The effects of molecule distance and the influence of fluorine substituents on the dynamics were investigated in detail, so that the path for studies is leveled. KW - elektronische Schalter KW - electrical switches KW - Azobenzol KW - Azobenzene KW - Fulgimide KW - self-assembled monolayer KW - selbstorganisierte Einzelschichten KW - metalorganic frameworks KW - theoretische Chemie KW - Eyring KW - Arrhenius KW - transition state KW - Übergangszustand KW - nichtadibatische Dynamik KW - non-adiabatic dynamic KW - Tully-Algorithmus KW - nichtadiabatische Kopplung KW - non-adiabatic coupling KW - freie Aktivierungsenthalpie KW - nicht-lineare Optik KW - non-linear optics KW - Hyperpolarisierbarkeit KW - hyperpolarizability KW - Moleküle in äußeren Feldern KW - Skalierungsmethode von Champagne KW - Sprungwahrscheinlichkeit KW - trajectory surface hopping KW - Anregungsspektren KW - Populationsanalyse KW - Quantenausbeute KW - quantum yield KW - E-Z Isomerisierung KW - trans-cis Isomerisierung KW - cis-trans Isomerisierung KW - Z-E Isomerisierung KW - Dichtefunktionaltheorie KW - DFT KW - Hartree Fock KW - SAM KW - MP2 KW - QM/MM KW - Pachkungsdichte KW - molekularer Abstand KW - D3 KW - Dispersionskorrektur KW - Kohn Sham KW - B3LYP KW - TDDFT KW - Berny-Algorithmus KW - Normalmodenanalyse KW - nichtlineare Optik KW - second harmonic generation KW - Frequenzverdopplung KW - SHG KW - SFG KW - statische Hyperpolarisierbarkeit KW - dynamische Hyperpolarisierbarkeit KW - static hyperpolarizability KW - dynamic hyperpolarizability KW - Tensor KW - Trajektorien KW - trajectory KW - AM1 KW - AM1/FOMO-CI KW - AM1/FOMO KW - Geometrieoptimierung KW - Elektronenstrukturrechnung KW - GAUSSIAN Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-459594 ER - TY - THES A1 - Melani, Giacomo T1 - From structural fluctuations to vibrational spectroscopy of adsorbates on surfaces T1 - Von Strukturfluktuationen bis zur Schwingungsspektroskopie von Adsorbaten auf Oberflächen BT - a theoretical study of H2O on α-Al2O3(0001) BT - eine theoretische Untersuchung von H2O auf α-Al2O3 (0001) N2 - Aluminum oxide is an Earth-abundant geological material, and its interaction with water is of crucial importance for geochemical and environmental processes. Some aluminum oxide surfaces are also known to be useful in heterogeneous catalysis, while the surface chemistry of aqueous oxide interfaces determines the corrosion, growth and dissolution of such materials. In this doctoral work, we looked mainly at the (0001) surface of α-Al 2 O 3 and its reactivity towards water. In particular, a great focus of this work is dedicated to simulate and address the vibrational spectra of water adsorbed on the α-alumina(0001) surface in various conditions and at different coverages. In fact, the main source of comparison and inspiration for this work comes from the collaboration with the “Interfacial Molecular Spectroscopy” group led by Dr. R. Kramer Campen at the Fritz-Haber Institute of the MPG in Berlin. The expertise of our project partners in surface-sensitive Vibrational Sum Frequency (VSF) generation spectroscopy was crucial to develop and adapt specific simulation schemes used in this work. Methodologically, the main approach employed in this thesis is Ab Initio Molecular Dynamics (AIMD) based on periodic Density Functional Theory (DFT) using the PBE functional with D2 dispersion correction. The analysis of vibrational frequencies from both a static and a dynamic, finite-temperature perspective offers the ability to investigate the water / aluminum oxide interface in close connection to experiment. The first project presented in this work considers the characterization of dissociatively adsorbed deuterated water on the Al-terminated (0001) surface. This particular structure is known from both experiment and theory to be the thermodynamically most stable surface termination of α-alumina in Ultra-High Vacuum (UHV) conditions. Based on experiments performed by our colleagues at FHI, different adsorption sites and products have been proposed and identified for D 2 O. While previous theoretical investigations only looked at vibrational frequencies of dissociated OD groups by staticNormal Modes Analysis (NMA), we rather employed a more sophisticated approach to directly assess vibrational spectra (like IR and VSF) at finite temperature from AIMD. In this work, we have employed a recent implementation which makes use of velocity-velocity autocorrelation functions to simulate such spectral responses of O-H(D) bonds. This approach allows for an efficient and qualitatively accurate estimation of Vibrational Densities of States (VDOS) as well as IR and VSF spectra, which are then tested against experimental spectra from our collaborators. In order to extend previous work on unimolecularly dissociated water on α-Al 2 O 3 , we then considered a different system, namely, a fully hydroxylated (0001) surface, which results from the reconstruction of the UHV-stable Al-terminated surface at high water contents. This model is then further extended by considering a hydroxylated surface with additional water molecules, forming a two-dimensional layer which serves as a potential template to simulate an aqueous interface in environmental conditions. Again, employing finite-temperature AIMD trajectories at the PBE+D2 level, we investigated the behaviour of both hydroxylated surface (HS) and the water-covered structure derived from it (known as HS+2ML). A full range of spectra, from VDOS to IR and VSF, is then calculated using the same methodology, as described above. This is the main focus of the second project, reported in Chapter 5. In this case, comparison between theoretical spectra and experimental data is definitely good. In particular, we underline the nature of high-frequency resonances observed above 3700 cm −1 in VSF experiments to be associated with surface OH-groups, known as “aluminols” which are a key fingerprint of the fully hydroxylated surface. In the third and last project, which is presented in Chapter 6, the extension of VSF spectroscopy experiments to the time-resolved regime offered us the opportunity to investigate vibrational energy relaxation at the α-alumina / water interface. Specifically, using again DFT-based AIMD simulations, we simulated vibrational lifetimes for surface aluminols as experimentally detected via pump-probe VSF. We considered the water-covered HS model as a potential candidate to address this problem. The vibrational (IR) excitation and subsequent relaxation is performed by means of a non-equilibrium molecular dynamics scheme. In such a scheme, we specifically looked at the O-H stretching mode of surface aluminols. Afterwards, the analysis of non-equilibrium trajectories allows for an estimation of relaxation times in the order of 2-4 ps which are in overall agreement with measured ones. The aim of this work has been to provide, within a consistent theoretical framework, a better understanding of vibrational spectroscopy and dynamics for water on the α-alumina(0001) surface,ranging from very low water coverage (similar to the UHV case) up to medium-high coverages, resembling the hydroxylated oxide in environmental moist conditions. N2 - Das Hauptziel dieser Doktorarbeit war die Untersuchung der Wechselwirkung zwischen Aluminiumoxid (α-Al2O3) und Wasser, wobei die (0001)-Oberfläche von α-Al2O3 im Fokus der Betrachtungen stand. Infolge der Entwicklung moderner oberflächensensitiver spektroskopischer Methoden, insbesondere in der Schwingungsspektroskopie, ist es inzwischen experimentell möglich, die Oberflächenchemie dieser Oxidmaterialien zu untersuchen und atomistische Informationen über ihre wässrigen Grenzflächen zu erhalten. Unsere Gruppe hat mit der Interfacial Molecular Spectroscopy Gruppe des Fritz-Haber-Instituts der MPG in Berlin zusammengearbeitet, deren Expertise in der oberflächensensitiven Vibrational Sum Frequency (VSF) Generation liegt. Diese Technik gestattet den spezifischen Nachweis von Adsorbatvibrationen, beispielsweise des Produkts der Wasserdissoziation und -adsorption. Zur theoretischen Untersuchung dieses Systems wurden verschiedene Berechnungsmethoden genutzt, wobei bevorzugt die Ab-initio-Molekulardynamik (AIMD) zum Einsatz kam. Darüber hinaus konzentrierten wir uns auf die Simulation von Schwingungsfrequenzen und -spektren für verschiedene Systeme unter Verwendung eines neuen, effizienten Algorithmus, der auf Grundlage klassischer Zeitkorrelationsfunktionen entwickelt wurde. Das erste Projekt untersuchte die einfachsten Adsorptionsprodukte von Wasserreaktionen auf der Al-terminierten α-Al2O3(0001)-Oberfläche, die unter Ultrahochvakuumbedingungen (UHV) als stabilste Struktur bekannt ist. Mit AIMD-basierten Methoden haben wir verschiedene Spezies simuliert, die aus unimolekular adsorbiertem Wasser stammen, und ihre Schwingungsfrequenzen im Vergleich zum Experiment bestimmt. In einem zweiten Projekt widmeten wir uns einer Situation, in der eine vollständig hydroxylierte α-Aluminiumoxid-Oberfläche mit einer ebenfalls vollständig hydroxylierten, aber um eine zusätzliche Wasserschicht erweiterten α-Aluminiumoxid-Oberfläche wechselwirkt. Diese beiden Strukturen dienen als Grundlage zur weitergehenden Untersuchung von Aluminiumoxid-Oberflächen mit größeren Wasser-Bedeckungsgraden unter Umgebungsbedingungen. Wiederum simulierten wir vollständige Schwingunsspektren (einschließlich IR und VSF). Hierzu wurden etablierte Methoden genutzt, die auf der Verwendung von Zeitkorrelationsfunktionen basieren, jedoch von uns im Rahmen dieser Doktorarbeit weiterentwickelt wurden. Schließlich haben wir in einem dritten Projekt in Zusammenarbeit mit Experimentatoren die Schwingungsrelaxation an der Wasser / α-Al2O3-Grenzfläche beschrieben. Motiviert durch Pump-Probe-VSF-Experimente zur Bestimmung der Schwingungslebensdauer adsorbierter OH-Spezies entwickelten und verwendeten wir einen AIMD-Ansatz zur Simulation der Anregungs- und Relaxationsprozesse. Auf Grundlage von Nichtgleichgewichtstrajektorien konnten wir auch eine Relaxationszeitskala für OH-Gruppen ermitteln, die zwischen 2 und 4 Pikosekunden beträgt und gut mit experimentellen Werten übereinstimmt. KW - theoretical chemistry KW - molecular dynamics KW - DFT KW - vibrational spectroscopy KW - theoretische Chemie KW - Molekulardynamik KW - DFT KW - Schwingungsspektroskopie Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-441826 ER - TY - JOUR A1 - Lindic, Tilen A1 - Sinha, Shreya A1 - Mattsson, Stefan A1 - Paulus, Beate T1 - Prediction of a model crystal structure for Ni2F5 by first-principles calculations JF - Zeitschrift für Naturforschung : B, Chemical sciences N2 - Electrochemical fluorination in anhydrous HF, also known as the Simons process, is a widely used industrial method for fluorination of organic compounds. Its mechanism, being not so well understood, has long been debated and is believed to involve higher valent nickel fluorides formed on the nickel-plated anode during the process. One of these is speculated to be Ni2F5, which was previously reported in the literature and assigned via infrared spectroscopy, but its crystal structure is not yet known. We have identified known crystal structures of compounds with similar stoichiometries as Ni2F5 and utilized them as a starting point for our periodic DFT investigations, applying the PBE+U method. Ni2F5 as the most stable polymorph was found to be of the same crystal structure as another mixed valent fluoride, Cr2F5. The calculated lattice parameters are a = 7.24 angstrom, b = 7.40 angstrom, c = 7.08 angstrom and beta = 118.9 degrees with an antiferromagnetic ordering of the nickel magnetic moments. KW - crystal structure prediction KW - DFT KW - Ni2F5 Y1 - 2022 U6 - https://doi.org/10.1515/znb-2022-0072 SN - 0932-0776 SN - 1865-7117 VL - 77 IS - 6 SP - 469 EP - 473 PB - De Gruyter CY - Berlin ER - TY - JOUR A1 - Laun, Konstantin A1 - Duffus, Benjamin R. A1 - Wahlefeld, Stefan A1 - Katz, Sagie A1 - Belger, Dennis Heinz A1 - Hildebrandt, Peter A1 - Mroginski, Maria Andrea A1 - Leimkühler, Silke A1 - Zebger, Ingo T1 - Infrared spectroscopy flucidates the inhibitor binding sites in a metal-dependent formate dehydrogenase JF - Chemistry - a European journal N2 - Biological carbon dioxide (CO2) reduction is an important step by which organisms form valuable energy-richer molecules required for further metabolic processes. The Mo-dependent formate dehydrogenase (FDH) from Rhodobacter capsulatus catalyzes reversible formate oxidation to CO2 at a bis-molybdopterin guanine dinucleotide (bis-MGD) cofactor. To elucidate potential substrate binding sites relevant for the mechanism, we studied herein the interaction with the inhibitory molecules azide and cyanate, which are isoelectronic to CO2 and charged as formate. We employed infrared (IR) spectroscopy in combination with density functional theory (DFT) and inhibition kinetics. One distinct inhibitory molecule was found to bind to either a non-competitive or a competitive binding site in the secondary coordination sphere of the active site. Site-directed mutagenesis of key amino acid residues in the vicinity of the bis-MGD cofactor revealed changes in both non-competitive and competitive binding, whereby the inhibitor is in case of the latter interaction presumably bound between the cofactor and the adjacent Arg587. KW - CO2 reduction KW - DFT KW - formate oxidation KW - inhibition kinetics KW - IR KW - spectroscopy KW - molybdoenzyme Y1 - 2022 U6 - https://doi.org/10.1002/chem.202201091 SN - 0947-6539 SN - 1521-3765 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Krivenkov, Maxim A1 - Golias, Evangelos A1 - Marchenko, Dmitry A1 - Sanchez-Barriga, Jaime A1 - Bihlmayer, Gustav A1 - Rader, Oliver A1 - Varykhalov, Andrei T1 - Nanostructural origin of giant Rashba effect in intercalated graphene JF - 2D Materials N2 - To enhance the spin-orbit interaction in graphene by a proximity effect without compromising the quasi-free-standing dispersion of the Dirac cones means balancing the opposing demands for strong and weak graphene-substrate interaction. So far, only the intercalation of Au under graphene/Ni(111) has proven successful, which was unexpected since graphene prefers a large separation (similar to 3.3 angstrom) from a Au monolayer in equilibrium. Here, we investigate this system and find the solution in a nanoscale effect. We reveal that the Au largely intercalates as nanoclusters. Our density functional theory calculations show that the graphene is periodically stapled to the Ni substrate, and this attraction presses graphene and Au nanoclusters together. This, in turn, causes a Rashba effect of the giant magnitude observed in experiment. Our findings show that nanopatterning of the substrate can be efficiently used for engineering of spin-orbit effects in graphene. KW - quasi-free-standing graphene KW - Ni(111) KW - gold intercalation KW - spin-orbit interaction KW - nanoclusters KW - STM KW - DFT Y1 - 2017 U6 - https://doi.org/10.1088/2053-1583/aa7ad8 SN - 2053-1583 VL - 4 IS - 3 PB - IOP Publ. Ltd. CY - Bristol ER -