Publications

@article{Schmiedmayer_2025a,

title = {Equivariant machine learning of electric field gradients—Predicting the quadrupolar coupling constant in the MAPbI_{3} phase transition},

author = {Bernhard Schmiedmayer and Jop W. Wolffs and Gilles A. de Wijs and Arno P. M. Kentgens and Jonathan Lahnsteiner and Georg Kresse},

doi = {10.1063/5.0301056},

year  = {2025},

date = {2025-12-02},

journal = {The Journal of Chemical Physics},

volume = {163},

pages = {214110},

abstract = {We present a strategy combining machine learning and first-principle calculations to achieve highly accurate nuclear quadrupolar coupling constant predictions. Our approach employs two distinct machine-learning frameworks: a machine-learned force field to generate molecular dynamics trajectories and a second model for electric field gradients that preserves rotational and translational symmetries. By incorporating thermostat-driven molecular dynamics sampling, we enable the prediction of quadrupolar coupling constants in highly disordered materials at finite temperatures. We validate our method by predicting the tetragonal-to-cubic phase transition temperature of the organic–inorganic halide perovskite MAPbI_{3}, obtaining results that closely match experimental data.},

keywords = {P03},

pubstate = {published},

tppubtype = {article}

}

@article{Wadhwa_2025a,

title = {Machine learning study of surface reconstructions of the Cu_{2}⁢O⁡(111) surface},

author = {Payal Wadhwa and Michael Schmid and Georg Kresse},

doi = {10.1103/sfjm-1gyr},

year  = {2025},

date = {2025-11-17},

journal = {Physical Review B},

volume = {112},

issue = {20},

pages = {205420},

abstract = {The atomic structure of the most stable reconstructed surface of cuprous oxide (Cu_{2}⁢O)⁢(111) surface has been a longstanding topic of debate. In this study, we develop on-the-fly machine-learned force fields (MLFFs) to systematically investigate the various reconstructions of the Cu_{2}⁢O⁡(111) surface under stoichiometric as well as O- and Cu-deficient or rich conditions, focusing on both (√3×√3⁢)R⁢30∘ and (2×2) supercells. By utilizing parallel tempering simulations supported by MLFFs, we confirm that the previously described nanopyramidal and Cu-deficient (1×1) structures are the lowest energy structures from moderately to strongly oxidizing conditions. In addition, we identify two promising nanopyramidal reconstructions at highly reducing conditions, a stoichiometric one and a Cu-rich one. Surface energy calculations performed using spin-polarized PBE, PBE+𝑈, r2⁢SCAN, and HSE06 functionals show that the previously known Cu-deficient configuration and nanopyramidal configurations are at the convex hull (and, thus, equilibrium structures) for all functionals, whereas the stability of the other structures depends on the functional and is therefore uncertain. Our findings demonstrate that on-the-fly trained MLFFs provide a simple, efficient, and rapid approach to explore the complex surface reconstructions commonly encountered in experimental studies, and also enhance our understanding of the stability of Cu_{2}⁢O⁡(111) surfaces.},

keywords = {P02, P03},

pubstate = {published},

tppubtype = {article}

}

@article{Huetner_2025a,

title = {Surface reconstructions govern ice nucleation on silver iodide},

author = {Johanna I. Hütner and Andrea Conti and David Kugler and Franziska Sabath and Kim Noelle Dreier and Hans-Georg Stammler and Florian Mittendorfer and Angelika Kühnle and Michael Schmid and Ulrike Diebold and Jan Balajka},

doi = {10.1126/sciadv.aea2378},

year  = {2025},

date = {2025-10-31},

journal = {Science Advances},

volume = {11},

number = {44},

pages = {eaea2378},

abstract = {Silver iodide (AgI) is among the most effective ice-nucleating agents, attributed to its close lattice match with hexagonal ice. However, the atomic-level mechanism behind its efficiency remains unclear. The basal surfaces of AgI are polar and inherently unstable, necessitating a compensation mechanism, such as surface reconstruction, which may disrupt the favorable lattice match with ice. We combine noncontact atomic force microscopy with advanced computational modeling to determine the atomic structure of basal AgI surfaces in ultrahigh vacuum. The Ag-terminated (0001) surface exhibits a (2 × 2) reconstruction with ordered Ag vacancies, preserving a hexagonal arrangement of surface atoms that facilitates epitaxial ice growth. In contrast, the I-terminated (0001) surface adopts a complex rectangular reconstruction, incompatible with continuous ice layer formation. These findings highlight the decisive role of surface atomic structure and indicate that the Ag-terminated basal plane is primarily responsible for efficient ice nucleation on AgI.},

keywords = {P02, P04},

pubstate = {published},

tppubtype = {article}

}

@article{Eder_2025a,

title = {Multi-technique characterization of rhodium gem-dicarbonyls on TiO_{2}(110)},

author = {Moritz Eder and Faith J. Lewis and Johanna I. Hütner and Panukorn Sombut and Maosheng Hao and David Rath and Paul Ryan and Jan Balajka and Margareta Wagner and Matthias Meier and Cesare Franchini and Gianfranco Pacchioni and Ulrike Diebold and Michael Schmid and Florian Libisch and Jiři Pavelec and Gareth S. Parkinson},

doi = {10.1039/D5SC04889C},

year  = {2025},

date = {2025-10-16},

journal = {Chemical Science},

abstract = {Gem-dicarbonyls of transition metals supported on metal (oxide) surfaces are common intermediates in heterogeneous catalysis. While infrared (IR) spectroscopy is a standard tool for detecting these species on powder catalysts, the ill-defined crystallographic environment renders data interpretation challenging. In this work, we apply a multi-technique surface science approach to investigate rhodium gem-dicarbonyls on a single-crystalline rutile TiO_{2}(110) surface. We combine spectroscopy, scanning probe microscopy, and density functional theory (DFT) to determine their location and coordination on the surface. IR spectroscopy shows the successful creation of gem-dicarbonyls on a titania single crystal by exposing deposited Rh atoms to CO gas, followed by annealing to 200–250 K. Low-temperature scanning tunneling microscopy (STM) and non-contact atomic force microscopy (nc-AFM) data reveal that these complexes are mostly aligned along the [001] crystallographic direction, corroborating theoretical predictions. Notably, X-ray photoelectron spectroscopy (XPS) data reveal multiple rhodium species on the surface, even when the IR spectra show only the signature of rhodium gem-dicarbonyls. As such, our results highlight the complex behavior of carbonyls on metal oxide surfaces, and demonstrate the necessity of multi-technique approaches for the adequate characterization of single-atom catalysts.},

keywords = {P02, P04, P07},

pubstate = {published},

tppubtype = {article}

}

@article{Zelenka_2025a,

title = {MgO–water interface: structure and surface dissolution depend on flow and pH},

author = {Moritz Zelenka and Ellen H. G. Backus},

doi = {10.1039/D5CP03295D},

year  = {2025},

date = {2025-10-10},

journal = {Physical Chemistry Chemical Physics},

abstract = {Magnesium oxide (MgO) is frequently in contact with water throughout numerous research and industrial applications and in nature. Remarkably, we found that there is a substantial influence on the interfacial structure and dissolution process whether water is flowing or static at the MgO(100) surface. Sum frequency generation spectroscopy revealed that flowing acidic solutions enhance the charging of the MgO surface, which leads to an increased net orientation of water close to the surface. Contrary, the MgO surface resembles a near neutrally charged state when in contact with static liquid for all tested solutions between pH 3 and pH 11. We explain this surprising observation with the dissolution of MgO in aqueous solutions, which effectively removes charge from the interfacial region. The continuous solution exchange due to flowing liquid shifts the equilibrium towards a more charged state in comparison to static liquid. Additionally, by investigating the transition from flowing to static liquid we found a reaction order of around 0.5 for the dissolution reaction with respect to the H^{+} concentration. Furthermore, the significant effect of the MgO surface dissolution on the interfacial structure points out that other solid–liquid interfaces with similar or higher solubility might exhibit similar properties.},

keywords = {P11},

pubstate = {published},

tppubtype = {article}

}

@article{Joseph_2025a,

title = {Coupling between small polarons and ferroelectricity in BaTiO_{3}},

author = {Darin Joseph and Cesare Franchini},

doi = {10.1103/5z43-rm34},

year  = {2025},

date = {2025-09-30},

urldate = {2025-09-30},

journal = {Physical Review Materials},

volume = {9},

pages = {094415},

abstract = {In this study, we investigate the formation of electron and hole small polarons in the prototypical ferroelectric material BaTiO_{3}, with a focus on their interaction with ferroelectric distortive fields. To accurately describe the ferroelectric phase in electronically correlated BaTiO_{3}, we employ the HSE06 hybrid density functional, which addresses the limitations of conventional density-functional theory (DFT) and Hubbard-corrected DFT+U models, providing a more precise depiction of both ferroelectric and polaronic behaviors. Our analysis spans three structural phases of BaTiO_{3}: cubic, tetragonal, and rhombohedral. We uncover a unique phase-dependent trend in electron-polaron stability, which progressively increases across the structural phases, peaking in the rhombohedral phase due to the constructive coupling between the polaron and ferroelectric phonon fields. In contrast, hole polarons exhibit a stability pattern largely unaffected by the phase transitions. Furthermore, we observe that polaron self-trapping significantly alters the local ferroelectric distortive pattern, which propagates to neighboring sites but has a minimal effect on the long-range macroscopic spontaneous polarization. Charge trapping is also associated with localized spin formation, opening new possibilities for enhanced functionalities in multiferroic materials.},

keywords = {P07},

pubstate = {published},

tppubtype = {article}

}

@article{Franchini_2025a,

title = {Spin Matters: A Multidisciplinary Roadmap to Understanding Spin Effects in Oxygen Evolution Reaction During Water Electrolysis},

author = {Emma van der Minne and Priscila Vensaus and Vadim Ratovskii and Seenivasan Hariharan and Jan Behrends and Cesare Franchini and Jonas Fransson and Sarnjeet S. Dhesi and Felix Gunkel and Florian Gossing and Georgios Katsoukis and Ulrike I. Kramm and Magalí Lingenfelde and Qianqian Lan and Yury V. Kolen’ko and Yang Li and Ramsundar Rani Mohan and Jeffrey McCord and Lingmei Ni and Eva Pavarini and Rossitza Pentcheva and David H. Waldeck and Michael Verhage and Anke Yu and Zhichuan J. Xu and Piero Torelli and Silvia Mauri and Narcis Avarvari and Anja Bieberle-Hütter and Christoph Baeumer},

doi = {10.1002/aenm.202503556},

year  = {2025},

date = {2025-09-01},

journal = {Advanced Energy Materials},

pages = {e03556},

abstract = {A central challenge in water electrolysis lies with the oxygen evolution reaction (OER) where the formation of molecular oxygen (O_{2}) is hindered by the constraint of angular momentum conservation. While the reactants OH^{-} or H_{2}O are diamagnetic (DM), the O_{2} product has a paramagnetic (PM) triplet ground state, requiring a change in spin configuration when being formed. This constraint has prompted interest in spin-selective catalysts as a means to facilitate OER. In this context, the roles of magnetism and chirality-induced spin selectivity (CISS) in promoting the OER reaction have recently been investigated through both theoretical and experimental studies. However, pinpointing the key principles and their relative contribution in mediating spin-enhancement remains a significant challenge. This roadmap offers a forward-looking perspective on current experimental trends and theoretical developments in spin-enhanced OER electrocatalysis and outlines strategic directions for integrating incisive experiments and operando approaches with computational modeling to disentangle key mechanisms. By providing a conceptual framework and identifying critical knowledge gaps, this perspective aims to guide researchers toward dedicated experimental and computational studies that will deepen the understanding of spin-induced OER enhancement and accelerate the development of next-generation catalysts.},

keywords = {P07},

pubstate = {published},

tppubtype = {article}

}

@article{Pollitt_2025a,

title = {Engineering Catalytic Efficiency by Thiolate-Protected Trimetallic (Cu, Pd, Au) Nanoclusters: Single-Atom Alloy Catalysts for Water–Gas Shift},

author = {Stephan Pollitt and Thomas Haunold and Sakiat Hossain and Gereon Behrendt and Michael Stöger-Pollach and Tokuhisa Kawawaki and Noelia Barrabés and Malte Behrens and Yuichi Negishi and Günther Rupprechter},

doi = {10.1021/acscatal.5c04165},

year  = {2025},

date = {2025-08-22},

journal = {ACS Catalysis},

volume = {15},

pages = {15459–15474},

abstract = {The “crude oil exodus” and energy transition will finally hinge on the availability of hydrogen. Catalytic processes like the water–gas shift (WGS) reaction may significantly contribute to its production and become crucial for utilizing alternative feedstocks. This work demonstrates how thiolate-protected gold nanoclusters can be employed as precursors for single-atom alloy (SAA) catalysts. The clusters serve as carriers of heteroatom dopants (Cu, Pd) while precisely maintaining 25 metal atoms per cluster (<1 nm). Using the 2PET ligand during synthesis led to high yield and cluster stability, but ligand exchange was required to link clusters to a ZnO support efficiently. Introducing pMBA as a ligand enabled a homogeneous cluster distribution on the ZnO surface, creating a well-defined catalyst with dual functionality. This SAA catalyst, outperforming a Cu/ZnO/Al_{2}O_{3} benchmark in WGS, may get industrial relevance when upscaled while still serving as a well-defined model system in catalysis. Thereby, it bridges the gap between practical applications and fundamental research. Pre- and postreaction analysis by XPS proved the presence of the dopants in the catalysts in the expected stoichiometry, showed changes in the electronic structures, but also revealed sulfur migration from the clusters/ligands to the support, forming ZnS. Furthermore, XPS unveiled a pretreatment-induced SMSI decoration effect, stabilizing the small particles during catalysis. (S)TEM indicated a homogeneous cluster distribution on ZnO after synthesis and proved small particle sizes throughout the experiments. In situ DRIFTS confirmed the accessibility of the dopant atoms by the reactant CO and also detected adsorbed byproducts. The precise size and doping control of thiolate-protected SAA nanoclusters, together with their catalytic performance, demonstrate the potential for targeted future investigations in a wide range of industrial applications.},

keywords = {P08},

pubstate = {published},

tppubtype = {article}

}

@article{Sidorowicz_2025a,

title = {Influence of MXene and TiO_{2} on the Performance of Microalgae-Derived Ru-Based Catalysts for CO_{2} Hydrogenation to Methane},

author = {Agnieszka Sidorowicz and Thomas Wicht and Michael Stöger-Pollach and Roberta Licheri and Giacomo Cao and Alessandro Concas and Günther Rupprechter},

doi = {10.1021/acscatal.5c04285},

year  = {2025},

date = {2025-08-19},

journal = {ACS Catalysis},

volume = {15},

pages = {15261–15278},

abstract = {Controlling the selectivity of CO_{2} hydrogenation to produce value-added fuels and chemicals is an actual challenge in catalysis research. The exact mechanisms underlying selectivity control often remain poorly understood, slowing the design of more efficient catalysts. In this study, we investigated RuO_{2} nanoparticles supported on MXene or TiO_{2} for CO_{2} hydrogenation at atmospheric pressure. Microalgal extracts were incorporated in the synthesis to explore their influence on catalyst properties, such as surface area, morphology, and elemental distribution. Although lower surface area and less uniform RuO_{2} dispersion were observed on MXenes than on TiO_{2}, after reductive pretreatment Ru/MXene exhibited superior catalytic activity, demonstrating that its unique textural properties and active site availability compensated for the lower surface area. A reducibility study revealed that MXene-supported catalysts undergo a more complex reduction process than those with TiO_{2} as the support. Additionally, bridge adsorption sites on MXene likely contributed to the enhanced CO_{2} hydrogenation activity, whereas TiO_{2} seemed to present a twin CO binding environment. Higher Ru loading on MXene increased the methane selectivity and conversion, whereas lower loading favored CO formation, highlighting the importance of optimizing catalyst loading. Operando diffuse reflectance infrared Fourier transform spectroscopy analysis revealed the critical role of methoxy intermediates in affecting the catalytic pathway, suggesting the potential for tuning synthesis conditions to improve yields. A partial encapsulation of Ru on MXene enhances the catalytic performance, while the stronger SMSI effect on TiO_{2} leads to complete encapsulation, reducing the catalytic efficiency. The findings underscore the promise of MXene as a support material for metal catalysts in CO_{2} hydrogenation toward environmentally friendly fuel production.},

keywords = {P08},

pubstate = {published},

tppubtype = {article}

}