@unpublished{64071, abstract = {{Stimulated by the renewed interest and recent developments in semi-empirical quantum chemical (SQC) methods for noncovalent interactions,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{62034, abstract = {{Effective single-particle theories, such as Hartree–Fock, density functional theory, and tight-binding, are limited by the computational cost of the self-consistent field (SCF) procedure, which typically scales cubically with the system size. This makes large-scale applications impractical without specialized algorithms and hardware. Here, we present the submatrix and graphical processing unit (GPU)-accelerated software implementation of the PTB tight-binding potential, realized in the open-source ptb codebase [M. Mueller, A. Katbashev, and S. Ehlert (2025). “grimme-lab/ptb: v3.8.1,” Zenodo. https://zenodo.org/records/17015872]. We first benchmark a traditional diagonalization-based SCF solver against density-matrix-based purification approaches, systematically varying both system size and computer hardware. Our findings show that the usage of GPUs permits shifting the boundaries to much larger systems than previously thought feasible, achieving an overall 10–15-fold performance speedup. Second, we introduce the implementation of a decomposition-type submatrix method, specifically designed for efficient operation on mid- to large-sized systems, to address the computational overhead associated with full-system diagonalization. We demonstrate that, from a certain dimension (≈104 basis functions) on, our submatrix method reduces the overall computational cost while maintaining acceptable numerical accuracy. Our study demonstrates the significance of the interplay between modern hardware, algorithmic considerations, and novel tight-binding methods, paving the way for further development in this direction.}}, author = {{Katbashev, Abylay and Schade, Robert and Laß, Michael and Müller, Marcel and Grimme, Stefan and Hansen, Andreas and Kühne, Thomas}}, issn = {{0021-9606}}, journal = {{The Journal of Chemical Physics}}, number = {{13}}, publisher = {{AIP Publishing}}, title = {{{Submatrix and GPU-accelerated implementation of density matrix tight-binding}}}, doi = {{10.1063/5.0271379}}, volume = {{163}}, year = {{2025}}, } @inproceedings{43228, abstract = {{The computation of electron repulsion integrals (ERIs) over Gaussian-type orbitals (GTOs) is a challenging problem in quantum-mechanics-based atomistic simulations. In practical simulations, several trillions of ERIs may have to be computed for every time step. In this work, we investigate FPGAs as accelerators for the ERI computation. We use template parameters, here within the Intel oneAPI tool flow, to create customized designs for 256 different ERI quartet classes, based on their orbitals. To maximize data reuse, all intermediates are buffered in FPGA on-chip memory with customized layout. The pre-calculation of intermediates also helps to overcome data dependencies caused by multi-dimensional recurrence relations. The involved loop structures are partially or even fully unrolled for high throughput of FPGA kernels. Furthermore, a lossy compression algorithm utilizing arbitrary bitwidth integers is integrated in the FPGA kernels. To our best knowledge, this is the first work on ERI computation on FPGAs that supports more than just the single most basic quartet class. Also, the integration of ERI computation and compression it a novelty that is not even covered by CPU or GPU libraries so far. Our evaluation shows that using 16-bit integer for the ERI compression, the fastest FPGA kernels exceed the performance of 10 GERIS ($10 \times 10^9$ ERIs per second) on one Intel Stratix 10 GX 2800 FPGA, with maximum absolute errors around $10^{-7}$ - $10^{-5}$ Hartree. The measured throughput can be accurately explained by a performance model. The FPGA kernels deployed on 2 FPGAs outperform similar computations using the widely used libint reference on a two-socket server with 40 Xeon Gold 6148 CPU cores of the same process technology by factors up to 6.0x and on a new two-socket server with 128 EPYC 7713 CPU cores by up to 1.9x.}}, author = {{Wu, Xin and Kenter, Tobias and Schade, Robert and Kühne, Thomas and Plessl, Christian}}, booktitle = {{2023 IEEE 31st Annual International Symposium on Field-Programmable Custom Computing Machines (FCCM)}}, pages = {{162--173}}, title = {{{Computing and Compressing Electron Repulsion Integrals on FPGAs}}}, doi = {{10.1109/FCCM57271.2023.00026}}, year = {{2023}}, } @article{45361, abstract = {{ The non-orthogonal local submatrix method applied to electronic structure–based molecular dynamics simulations is shown to exceed 1.1 EFLOP/s in FP16/FP32-mixed floating-point arithmetic when using 4400 NVIDIA A100 GPUs of the Perlmutter system. This is enabled by a modification of the original method that pushes the sustained fraction of the peak performance to about 80%. Example calculations are performed for SARS-CoV-2 spike proteins with up to 83 million atoms. }}, author = {{Schade, Robert and Kenter, Tobias and Elgabarty, Hossam and Lass, Michael and Kühne, Thomas and Plessl, Christian}}, issn = {{1094-3420}}, journal = {{The International Journal of High Performance Computing Applications}}, keywords = {{Hardware and Architecture, Theoretical Computer Science, Software}}, publisher = {{SAGE Publications}}, title = {{{Breaking the exascale barrier for the electronic structure problem in ab-initio molecular dynamics}}}, doi = {{10.1177/10943420231177631}}, year = {{2023}}, } @unpublished{40982, abstract = {{Effective photoinduced charge transfer makes molecular bimetallic assemblies attractive for applications as active light induced proton reduction systems. For a more sustainable future, development of competitive base metal dyads is mandatory. However, the electron transfer mechanisms from the photosensitizer to the proton reduction catalyst in base metal dyads remain so far unexplored. We study a Fe-Co dyad that exhibits photocatalytic H2 production activity using femtosecond X-ray emission spectroscopy, complemented by ultrafast optical spectroscopy and theoretical time-dependent DFT calculations, to understand the electronic and structural dynamics after photoexcitation and during the subsequent charge transfer process from the FeII photosensitizer to the cobaloxime catalyst. Using this novel approach, the simultaneous measurement of the transient Kalpha X-ray emission at the iron and cobalt K-edges in a two-colour experiment is enabled making it possible to correlate the excited state dynamics to the electron transfer processes. The methodology, therefore, provides a clear and direct spectroscopic evidence of the Fe->Co electron transfer responsible for the proton reduction activity.}}, author = {{Nowakowski, Michał and Huber-Gedert, Marina and Elgabarty, Hossam and Kubicki, Jacek and Kertem, Ahmet and Lindner, Natalia and Khakhulin, Dimitry and Lima, Frederico Alves and Choi, Tae-Kyu and Biednov, Mykola and Piergies, Natalia and Zalden, Peter and Kubicek, Katerina and Rodriguez-Fernandez, Angel and Salem, Mohammad Alaraby and Kühne, Thomas and Gawelda, Wojciech and Bauer, Matthias}}, booktitle = {{arxiv}}, title = {{{Ultrafast two-colour X-ray emission spectroscopy reveals excited state landscape in a base metal dyad}}}, year = {{2023}}, } @article{34300, abstract = {{AbstractThe solvation of ions changes the physical, chemical and thermodynamic properties of water, and the microscopic origin of this behaviour is believed to be ion-induced perturbation of water’s hydrogen-bonding network. Here we provide microscopic insights into this process by monitoring the dissipation of energy in salt solutions using time-resolved terahertz–Raman spectroscopy. We resonantly drive the low-frequency rotational dynamics of water molecules using intense terahertz pulses and probe the Raman response of their intermolecular translational motions. We find that the intermolecular rotational-to-translational energy transfer is enhanced by highly charged cations and is drastically reduced by highly charged anions, scaling with the ion surface charge density and ion concentration. Our molecular dynamics simulations reveal that the water–water hydrogen-bond strength between the first and second solvation shells of cations increases, while it decreases around anions. The opposite effects of cations and anions on the intermolecular interactions of water resemble the effects of ions on the stabilization and denaturation of proteins.}}, author = {{Balos, Vasileios and Kaliannan, Naveen Kumar and Elgabarty, Hossam and Wolf, Martin and Kühne, Thomas and Sajadi, Mohsen}}, issn = {{1755-4330}}, journal = {{Nature Chemistry}}, keywords = {{General Chemical Engineering, General Chemistry}}, number = {{9}}, pages = {{1031--1037}}, publisher = {{Springer Science and Business Media LLC}}, title = {{{Time-resolved terahertz–Raman spectroscopy reveals that cations and anions distinctly modify intermolecular interactions of water}}}, doi = {{10.1038/s41557-022-00977-2}}, volume = {{14}}, year = {{2022}}, } @article{33679, author = {{Zhang, Ruiming and Ruan, Wei and Yu, Junyao and Gao, Libo and Berger, Helmuth and Forró, László and Watanabe, Kenji and Taniguchi, Takashi and Ranjbar, Ahmad and Belosludov, Rodion V. and Kühne, Thomas and Bahramy, Mohammad Saeed and Xi, Xiaoxiang}}, issn = {{2469-9950}}, journal = {{Physical Review B}}, number = {{8}}, publisher = {{American Physical Society (APS)}}, title = {{{Second-harmonic generation in atomically thin 1T−TiSe2 and its possible origin from charge density wave transitions}}}, doi = {{10.1103/physrevb.105.085409}}, volume = {{105}}, year = {{2022}}, } @article{33682, author = {{Khazaei, Mohammad and Ranjbar, Ahmad and Kang, Yoon‐Gu and Liang, Yunye and Khaledialidusti, Rasoul and Bae, Soungmin and Raebiger, Hannes and Wang, Vei and Han, Myung Joon and Mizoguchi, Hiroshi and Bahramy, Mohammad S. and Kühne, Thomas and Belosludov, Rodion V. and Ohno, Kaoru and Hosono, Hideo}}, issn = {{1616-301X}}, journal = {{Advanced Functional Materials}}, keywords = {{Electrochemistry, Condensed Matter Physics, Biomaterials, Electronic, Optical and Magnetic Materials}}, number = {{20}}, publisher = {{Wiley}}, title = {{{Electronic Structures of Group III–V Element Haeckelite Compounds: A Novel Family of Semiconductors, Dirac Semimetals, and Topological Insulators}}}, doi = {{10.1002/adfm.202110930}}, volume = {{32}}, year = {{2022}}, } @article{33676, author = {{Schulze Lammers, Bertram and López-Salas, Nieves and Stein Siena, Julya and Mirhosseini, Hossein and Yesilpinar, Damla and Heske, Julian Joachim and Kühne, Thomas and Fuchs, Harald and Antonietti, Markus and Mönig, Harry}}, issn = {{1936-0851}}, journal = {{ACS Nano}}, keywords = {{General Physics and Astronomy, General Engineering, General Materials Science}}, number = {{9}}, pages = {{14284--14296}}, publisher = {{American Chemical Society (ACS)}}, title = {{{Real-Space Identification of Non-Noble Single Atomic Catalytic Sites within Metal-Coordinated Supramolecular Networks}}}, doi = {{10.1021/acsnano.2c04439}}, volume = {{16}}, year = {{2022}}, } @unpublished{33678, abstract = {{Accelerated chemistry at the interface with water has received increasing attention. The mechanisms behind the enhanced reactivity On-Water are not yet clear. In this work we use a Langevin scheme in the spirit of second generation Car-Parrinello to accelerate the second-order density functional Tight-Binding (DFTB2) method in order to investigate the free energy of two Diels-Alder reaction On-Water: the cycloaddition between cyclopentadiene and ethyl cinnamate or thionocinnamate. The only difference between the reactants is the substitution of a carbonyl oxygen for a thiocarbonyl sulfur, making possible the distinction between them as strong and weak hydrogen-bond acceptors. We find a different mechanism for the reaction during the transition states and uncover the role of hydrogen bonds along with the reaction path. Our results suggest that acceleration of Diels-Alder reactions do not arise from an increased number of hydrogen bonds at the transition state and charge transfer plays a significant role. However, the presence of water and hydrogen-bonds is determinant for the catalysis of these reactions.}}, author = {{Henao Aristizabal, Andres and Gohar, Yomna and Whilhelm, René and Kühne, Thomas}}, publisher = {{American Chemical Society (ACS)}}, title = {{{On the Role of Hydrogen Bond Strength and Charge Transfer of a Diels-Alder Reaction On-Water: Semiempirical and Free Energy Calculations.}}}, year = {{2022}}, } @article{33680, author = {{Khajehpasha, Ehsan Rahmatizad and Finkler, Jonas A. and Kühne, Thomas and Ghasemi, Alireza}}, issn = {{2469-9950}}, journal = {{Physical Review B}}, number = {{14}}, publisher = {{American Physical Society (APS)}}, title = {{{CENT2: Improved charge equilibration via neural network technique}}}, doi = {{10.1103/physrevb.105.144106}}, volume = {{105}}, year = {{2022}}, } @article{33686, author = {{Elizabeth, Amala and Sahoo, Sudhir K. and Phirke, Himanshu and Kodalle, Tim and Kühne, Thomas and Audinot, Jean-Nicolas and Wirtz, Tom and Redinger, Alex and Kaufmann, Christian A. and Mirhosseini, Hossein and Mönig, Harry}}, issn = {{1944-8244}}, journal = {{ACS Applied Materials & Interfaces}}, keywords = {{General Materials Science}}, number = {{29}}, pages = {{34101--34112}}, publisher = {{American Chemical Society (ACS)}}, title = {{{Surface Passivation and Detrimental Heat-Induced Diffusion Effects in RbF-Treated Cu(In,Ga)Se2 Solar Cell Absorbers}}}, doi = {{10.1021/acsami.2c08257}}, volume = {{14}}, year = {{2022}}, } @article{33689, author = {{Raghuwanshi, Mohit and Chugh, Manjusha and Sozzi, Giovanna and Kanevce, Ana and Kühne, Thomas and Mirhosseini, Hossein and Wuerz, Roland and Cojocaru‐Mirédin, Oana}}, issn = {{0935-9648}}, journal = {{Advanced Materials}}, keywords = {{Mechanical Engineering, Mechanics of Materials, General Materials Science}}, number = {{37}}, publisher = {{Wiley}}, title = {{{Fingerprints Indicating Superior Properties of Internal Interfaces in Cu(In,Ga)Se 2 Thin‐Film Solar Cells}}}, doi = {{10.1002/adma.202203954}}, volume = {{34}}, year = {{2022}}, } @article{33690, author = {{Ibaceta-Jaña, Josefa and Chugh, Manjusha and Novikov, Alexander S. and Mirhosseini, Hossein and Kühne, Thomas and Szyszka, Bernd and Wagner, Markus R. and Muydinov, Ruslan}}, issn = {{1932-7447}}, journal = {{The Journal of Physical Chemistry C}}, keywords = {{Surfaces, Coatings and Films, Physical and Theoretical Chemistry, General Energy, Electronic, Optical and Magnetic Materials}}, number = {{38}}, pages = {{16215--16226}}, publisher = {{American Chemical Society (ACS)}}, title = {{{Do Lead Halide Hybrid Perovskites Have Hydrogen Bonds?}}}, doi = {{10.1021/acs.jpcc.2c02984}}, volume = {{126}}, year = {{2022}}, } @article{33683, author = {{Lepre, Enrico and Heske, Julian Joachim and Nowakowski, Michal and Scoppola, Ernesto and Zizak, Ivo and Heil, Tobias and Kühne, Thomas and Antonietti, Markus and López-Salas, Nieves and Albero, Josep}}, issn = {{2211-2855}}, journal = {{Nano Energy}}, keywords = {{Electrical and Electronic Engineering, General Materials Science, Renewable Energy, Sustainability and the Environment}}, publisher = {{Elsevier BV}}, title = {{{Ni-based electrocatalysts for unconventional CO2 reduction reaction to formic acid}}}, doi = {{10.1016/j.nanoen.2022.107191}}, volume = {{97}}, year = {{2022}}, } @misc{33688, author = {{Balos, Vasileios and Kaliannan, Naveen Kumar and Elgabarty, Hossam and Wolf, Martin and Kühne, Thomas and Sajadi, Mohsen}}, publisher = {{LibreCat University}}, title = {{{Time resolved THz-Raman spectroscopy reveals that cations and anions distinctly modify intermolecular interactions of water}}}, doi = {{10.5281/ZENODO.6514905}}, year = {{2022}}, } @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}}, } @unpublished{33493, abstract = {{Electronic structure calculations have been instrumental in providing many important insights into a range of physical and chemical properties of various molecular and solid-state systems. Their importance to various fields, including materials science, chemical sciences, computational chemistry and device physics, is underscored by the large fraction of available public supercomputing resources devoted to these calculations. As we enter the exascale era, exciting new opportunities to increase simulation numbers, sizes, and accuracies present themselves. In order to realize these promises, the community of electronic structure software developers will however first have to tackle a number of challenges pertaining to the efficient use of new architectures that will rely heavily on massive parallelism and hardware accelerators. This roadmap provides a broad overview of the state-of-the-art in electronic structure calculations and of the various new directions being pursued by the community. It covers 14 electronic structure codes, presenting their current status, their development priorities over the next five years, and their plans towards tackling the challenges and leveraging the opportunities presented by the advent of exascale computing.}}, author = {{Gavini, Vikram and Baroni, Stefano and Blum, Volker and Bowler, David R. and Buccheri, Alexander and Chelikowsky, James R. and Das, Sambit and Dawson, William and Delugas, Pietro and Dogan, Mehmet and Draxl, Claudia and Galli, Giulia and Genovese, Luigi and Giannozzi, Paolo and Giantomassi, Matteo and Gonze, Xavier and Govoni, Marco and Gulans, Andris and Gygi, François and Herbert, John M. and Kokott, Sebastian and Kühne, Thomas and Liou, Kai-Hsin and Miyazaki, Tsuyoshi and Motamarri, Phani and Nakata, Ayako and Pask, John E. and Plessl, Christian and Ratcliff, Laura E. and Richard, Ryan M. and Rossi, Mariana and Schade, Robert and Scheffler, Matthias and Schütt, Ole and Suryanarayana, Phanish and Torrent, Marc and Truflandier, Lionel and Windus, Theresa L. and Xu, Qimen and Yu, Victor W. -Z. and Perez, Danny}}, booktitle = {{arXiv:2209.12747}}, title = {{{Roadmap on Electronic Structure Codes in the Exascale Era}}}, year = {{2022}}, } @unpublished{32404, abstract = {{The CP2K program package, which can be considered as the swiss army knife of atomistic simulations, is presented with a special emphasis on ab-initio molecular dynamics using the second-generation Car-Parrinello method. After outlining current and near-term development efforts with regards to massively parallel low-scaling post-Hartree-Fock and eigenvalue solvers, novel approaches on how we plan to take full advantage of future low-precision hardware architectures are introduced. Our focus here is on combining our submatrix method with the approximate computing paradigm to address the immanent exascale era.}}, author = {{Kühne, Thomas and Plessl, Christian and Schade, Robert and Schütt, Ole}}, booktitle = {{arXiv:2205.14741}}, title = {{{CP2K on the road to exascale}}}, year = {{2022}}, }