@unpublished{64071, abstract = {{Stimulated by the renewed interest and recent developments in semi-empirical quantum chemical (SQC) methods for noncovalent interactions, we examine the properties of liquid water at ambient conditions by means of molecular dynamics (MD) simulations, both with the conventional NDDO-type (neglect of diatomic differential overlap) methods, e.g. AM1 and PM6, and with DFTB-type (density-functional tight-binding) methods, e.g. DFTB2 and GFN-xTB. Besides the original parameter sets, some specifically reparametrized SQC methods (denoted as AM1-W, PM6-fm, and DFTB2-iBi) targeting various smaller water systems ranging from molecular clusters to bulk are considered as well. The quality of these different SQC methods for describing liquid water properties at ambient conditions are assessed by comparison to well-established experimental data and also to BLYP-D3 density functional theory-based ab initio MD simulations. Our analyses reveal that static and dynamics properties of bulk water are poorly described by all considered SQC methods with the original parameters, regardless of the underlying theoretical models, with most of the methods suffering from too weak hydrogen bonds and hence predicting a far too fluid water with highly distorted hydrogen bond kinetics. On the other hand, the reparametrized force-matchcd PM6-fm method is shown to be able to quantitatively reproduce the static and dynamic features of liquid water, and thus can be used as a computationally efficient alternative to electronic structure-based MD simulations for liquid water that requires extended length and time scales. DFTB2-iBi predicts a slightly overstructured water with reduced fluidity, whereas AM1-W gives an amorphous ice-like structure for water at ambient conditions.}}, author = {{Wu, Xin and Elgabarty, Hossam and Alizadeh, Vahideh and Henao Aristizabal, Andres and Zysk, Frederik and Plessl, Christian and Ehlert, Sebastian and Hutter, Jürg and Kühne, Thomas D.}}, title = {{{Benchmarking semi-empirical quantum chemical methods on liquid water}}}, year = {{2025}}, } @article{56080, abstract = {{CPO‐27 is a metal‐organic framework (MOF) with coordinatively unsaturated metal centers (open metal sites). It is therefore an ideal host material for small guest molecules, including water. This opens up numerous possible applications, such as proton conduction, humidity sensing, water harvesting, or adsorption‐driven heat pumps. For all of these applications, profound knowledge of the adsorption and desorption of water in the micropores is mandatory. The hydration and water structure in CPO‐27‐M (M = Zn or Cu) is investigated using water vapor sorption, Fourier transform infrared (FTIR) spectroscopy, density functional theory (DFT) calculations, and molecular dynamics simulation. In the pores of CPO‐27‐Zn, water binds as a ligand to the Zn center. Additional water molecules are stepwise incorporated at defined positions, forming a network of H‐bonds with the framework and with each other. In CPO‐27‐Cu, hydration proceeds by an entirely different mechanism. Here, water does not coordinate to the metal center, but only forms H‐bonds with the framework; pore filling occurs mostly in a single step, with the open metal site remaining unoccupied. Water in the pores forms clusters with extensive intra‐cluster H‐bonding.}}, author = {{Kloß, Marvin and Beerbaum, Michael and Baier, Dominik and Weinberger, Christian and Zysk, Frederik and Elgabarty, Hossam and Kühne, Thomas D. and Tiemann, Michael}}, issn = {{2196-7350}}, journal = {{Advanced Materials Interfaces}}, number = {{35}}, pages = {{2400476}}, publisher = {{Wiley}}, title = {{{Understanding Hydration in CPO‐27 Metal‐Organic Frameworks: Strong Impact of the Chemical Nature of the Metal (Cu, Zn)}}}, doi = {{10.1002/admi.202400476}}, volume = {{11}}, year = {{2024}}, } @article{33691, abstract = {{Near ambient pressure XPS in nitrogen atmosphere was utilized to investigate gas-solid interactions within porous SiO2 films ranging from 30 to 75 nm thickness. The films were differentiated in terms of porosity and roughness. The XPS N1s core levels of the N2 gas in presence of the SiO2 samples showed variations in width, binding energy and line shape. The width correlated with the surface charge induced in the dielectric films upon X-ray irradiation. The observed different binding energies observed for the N1s peak can only partly be associated with intrinsic work function differences between the samples, opening the possibility that the effect of physisorption at room temperature could be detected by a shift in the measured binding energy. However, the signals also show an increasing asymmetry with rising surface charge. This might be associated with the formation of vertical electrical gradients within the dielectric porous thin films, which complicates the assignment of binding energy positions to specific surface-related effects. With the support of Monte Carlo and first principles density functional theory calculations, the observed shifts were discussed in terms of the possible formation of transitory dipoles upon N2 physisorption within the porous SiO2 films.}}, author = {{de los Arcos, Teresa and Weinberger, Christian and Zysk, Frederik and Raj Damerla, Varun and Kollmann, Sabrina and Vieth, Pascal and Tiemann, Michael and Kühne, Thomas and Grundmeier, Guido}}, issn = {{0169-4332}}, journal = {{Applied Surface Science}}, keywords = {{Surfaces, Coatings and Films, Condensed Matter Physics, Surfaces and Interfaces, General Physics and Astronomy, General Chemistry}}, publisher = {{Elsevier BV}}, title = {{{Challenges in the interpretation of gas core levels for the determination of gas-solid interactions within dielectric porous films by ambient pressure XPS}}}, doi = {{10.1016/j.apsusc.2022.154525}}, volume = {{604}}, year = {{2022}}, } @article{33685, abstract = {{In the spatial confinement of cylindrical mesopores with diameters of a few nanometers, water molecules experience restrictions in hydrogen bonding. This leads to a different behavior regarding the molecular orientational freedom (‘structure of water') compared to the bulk liquid state. In addition to the pore size, the behavior is also strongly affected by the strength of the pore wall-to-water interactions, that is, the pore wall polarity. In this work, this is studied both experimentally and theoretically. The surface polarity of mesoporous silica (SiO2) is modified by functionalization with trimethylsilyl moieties, resulting in a change from a hydrophilic (pristine) to a hydrophobic pore wall. The mesopore surface is characterized by N2 and H2O sorption experiments. Those results are combined with IR spectroscopy to investigate pore wall-to-water interactions leading to different structures of water in the mesopore. Furthermore, the water's structure is studied theoretically to gain deeper insight into the interfacial interactions. For this purpose, the structure of water is analyzed by pairing densities, coordination, and angular distributions with a novel adaptation of surface-specific sum-frequency generation calculation for pore environments.}}, author = {{Weinberger, Christian and Zysk, Frederik and Hartmann, Marc and Kaliannan, Naveen and Keil, Waldemar and Kühne, Thomas and Tiemann, Michael}}, issn = {{2196-7350}}, journal = {{Advanced Materials Interfaces}}, keywords = {{Mechanical Engineering, Mechanics of Materials}}, number = {{20}}, publisher = {{Wiley}}, title = {{{The Structure of Water in Silica Mesopores – Influence of the Pore Wall Polarity}}}, doi = {{10.1002/admi.202200245}}, volume = {{9}}, year = {{2022}}, } @article{33675, abstract = {{The influence of different polymer side chains on the vapor phase infiltration with TMA is investigated and supported by DFT-calculations.}}, author = {{Mai, Lukas and Maniar, Dina and Zysk, Frederik and Schöbel, Judith and Kühne, Thomas and Loos, Katja and Devi, Anjana}}, issn = {{1477-9226}}, journal = {{Dalton Transactions}}, keywords = {{Inorganic Chemistry}}, number = {{4}}, pages = {{1384--1394}}, publisher = {{Royal Society of Chemistry (RSC)}}, title = {{{Influence of different ester side groups in polymers on the vapor phase infiltration with trimethyl aluminum}}}, doi = {{10.1039/d1dt03753f}}, volume = {{51}}, year = {{2021}}, } @article{41024, author = {{Gujt, Jure and Zimmer, Peter and Zysk, Frederik and Süß, Vicky and Felser, Claudia and Bauer, Matthias and Kühne, Thomas}}, issn = {{2329-7778}}, journal = {{Structural Dynamics}}, keywords = {{Spectroscopy, Condensed Matter Physics, Instrumentation, Radiation}}, number = {{3}}, publisher = {{AIP Publishing}}, title = {{{Water structure near the surface of Weyl semimetals as catalysts in photocatalytic proton reduction}}}, doi = {{10.1063/4.0000008}}, volume = {{7}}, year = {{2020}}, }