Publications

@article{Montero_2026c,

title = {Dynamical properties of ab initio water from machine-learning potentials},

author = {Pablo Montero de Hijes and L. Neubeck and Georg Kresse and Christoph Dellago},

doi = {10.1063/5.0348453},

year  = {2026},

date = {2026-08-17},

journal = {The Journal of Chemical Physics},

volume = {165},

pages = {074502},

abstract = {We assess the dynamical properties of liquid water predicted by several density functionals using machine-learning interatomic potentials. MACE models were trained for SCAN, RPBE-D3/zd, revPBE-D3/zd, revPBE0-D3/BJ, PBE0-D3/zd, and PBE0-D3/BJ using previously reported \emph{ab initio} datasets. We compare translational, rotational, and viscous dynamics through time-correlation functions, which resolve relaxation processes across different timescales, and through the corresponding long-time kinetic coefficients. The diffusion coefficient, second-rank orientational relaxation time, and shear viscosity reveal systematic differences among functionals. Part of these differences can be rationalized as shifts along the phase diagram, as comparisons relative to the melting temperature of each functional reduce the spread in the dynamical observables. Among the functionals considered, RPBE-D3/zd provides the best overall agreement with experiment. We, therefore, perform a broader validation of RPBE-D3/zd using a Behler–Parrinello neural-network potential over a wide range of temperatures, densities, and pressures. The model reproduces the magnitude and anomalous pressure dependence of the diffusion coefficient, gives generally good viscosities, and captures the temperature dependence of the rotational relaxation time.},

note = {2026 JCP Emerging Investigators Special Collection},

keywords = {P03, P12},

pubstate = {published},

tppubtype = {article}

}

@article{Maqbool_2026c,

title = {Upcycling Pond Coal Ash for CO Oxidation: An Operando Spectroscopic Study},

author = {Qaisar Maqbool and Susanne Gross and Mandakhsaikhan Luvsandagva and Oyun-Erdene Gendenjamts and Hamilton Uchenna Aharanwa and Nagihan Aydin and Michael Stöger-Pollach and Altansukh Batnasan and Nyamdelger Shirchinnamjil and Günther Rupprechter },

doi = {10.1021/acssusresmgt.6c00299},

year  = {2026},

date = {2026-08-16},

journal = {ACS Sustainable Resource Management},

abstract = {Pond coal ash (PCA) is an abundant industrial waste whose disposal poses significant environmental challenges; however, its intrinsic mineral complexity offers opportunities for sustainable catalytic upcycling. In this work, pond coal ash collected from a thermal power plant in Mongolia was upcycled into functional catalysts for CO oxidation through wet magnetic separation, yielding magnetic (M-PCA) and non-magnetic (NM-PCA) fractions. Comprehensive characterization using X-ray fluorescence, X-ray diffraction with Rietveld refinement, N_{2} physisorption, and TEM-EDX mapping revealed comparable bulk elemental compositions but pronounced differences in crystalline phase assemblies, spatial elemental distribution, and surface heterogeneity between the two fractions. While both materials are dominated by oxide-silicate and Ca-rich phases after oxidative pretreatment, NM-PCA uniquely exhibits a higher degree of chemical and structural heterogeneity, including localized iron-rich domains and a broader distribution of defect-associated surface environments. Temperature-programmed oxidation demonstrated enhanced oxygen uptake for NM-PCA, indicating superior oxygen activation capacity despite its lower bulk iron content. Steady-state CO oxidation experiments showed that NM-PCA consistently outperforms M-PCA, achieving ∼44% higher CO conversion at 400 °C and ∼31% higher conversion at 450 °C. For the first time, operando temperature-programmed DRIFTS coupled with GC-MS was employed to directly elucidate the CO oxidation mechanism over pond coal ash-derived catalysts, revealing temperature-dependent CO adsorption on aluminosilicate oxides containing surface sites, transient stabilization of CO_{2} as surface carbonate species on Ca-rich phases, and high-temperature carbonate decomposition contributing to CO_{2} release. These findings demonstrate that catalytic performance is governed by the mineralogical organization and microstructural distribution of the constituent phases, rather than by the bulk iron content alone, establishing a sustainable pathway for upcycling pond coal ash into low-cost catalysts for environmental remediation.},

keywords = {P08},

pubstate = {published},

tppubtype = {article}

}

@article{Maqbool_2026b,

title = {Dynamic AuZn Phase Formation Stabilizes CO_{2} Hydrogenation to Syngas},

author = {Qaisar Maqbool and Klaus Dobrezberger and Günther Rupprechter},

doi = {https://doi.org/10.1002/cnma.70343},

year  = {2026},

date = {2026-08-05},

journal = {ChemNanoMat},

volume = {12},

issue = {8},

pages = {e70343},

abstract = {Controlling selectivity and activity in CO_{2} hydrogenation remains a challenge in the synthesis of sustainable fuels. We investigated a 1 wt.% Au/ZnO catalyst by AUROlite for CO_{2} hydrogenation at 20 bar, combining kinetic evaluation with temperature-programmed desorption (TPD), scanning transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy (STEM-EDX) and X-ray diffraction (XRD) characterization to link performance to structural dynamics. Au/ZnO exhibited high activity for reverse water–gas shift (RWGS). This enhanced intrinsic activity correlates well with the small Au particle size of ∼2 nm. During 24-h stability tests, CO_{2} conversion and CO and CH_{4} yields remained constant, concurrent with the emergence of an AuZn phase in XRD. H2-TPD revealed pronounced changes in the catalyst surface, with the initial H_{2} desorption at 155 °C disappearing after reaction, consistent with significant surface restructuring and possibly alloying. STEM-EDX indicated intimate Au–ZnO contact after reaction, a configuration consistent with the alloyed domains inferred from XRD and with the observed catalytic behavior. The results suggest that the small Au particle size together with dynamic AuZn phase formation and ZnO redeposition stabilizes active sites, reflected in the nearly constant CO_{2} conversion and CO and CH_{2} yields. Further mechanistic studies into the role of the AuZn phase are proposed to clarify its influence and to guide catalyst design for CO_{2} valorization.},

keywords = {P08},

pubstate = {published},

tppubtype = {article}

}

@article{Falkner_2026a,

title = {Unbiased exploration of the transition region in ice nucleation using the NpH ensemble},

author = {Sebastian Falkner and Nadine Schwierz and Pablo Montero de Hijes},

doi = {10.1063/5.0336532},

year  = {2026},

date = {2026-08-05},

urldate = {2026-08-05},

journal = {The Journal of Chemical Physics},

volume = {165},

pages = {054504},

abstract = {In this work, we employ the isenthalpic–isobaric (NpH) ensemble to sample the transition region of ice nucleation without any external bias, thereby avoiding potentially artificial memory effects introduced by projections onto collective variables. Within this framework, we identify relevant degrees of freedom that expose the intrinsically non-Markovian nature of the largest nucleus size, indicating that it is not sufficient on its own to describe nucleation dynamics. The NpH ensemble leads to long-lived nuclei through the coupling between latent heat release or absorption and temperature fluctuations. As a result, nuclei persist over extended timescales and undergo a slow internal evolution, which we refer to as aging. A signature of this behavior is the emergence of hysteresis in the largest cluster size–temperature plane. To quantify these effects, we perform a structural analysis based on a high-dimensional set of descriptors, which we project onto a low-dimensional latent space using a neural network-based autoencoder. This approach reveals the existence of structurally distinct classes of nuclei with similar sizes and temperatures. Finally, we compare the nucleus sizes obtained with this approach with those from previous studies employing different methodologies, finding good agreement.},

note = {Festschrift in honor of Christoph Dellago},

keywords = {P12},

pubstate = {published},

tppubtype = {article}

}

@article{Maqbool_2026a,

title = {Upcycling Bio and Battery Waste Into Multivalent Calcium–Manganese Oxide Nanocomposites},

author = {Qaisar Maqbool and Hamilton Uchenna Aharanwa and Thomas Haunold and Saba Yaseen and Nagihan Aydin and Werner Artner and Michael Stöger-Pollach and Günther Rupprechter},

doi = {https://doi.org/10.1002/cmtd.70149},

year  = {2026},

date = {2026-08-04},

journal = {Chemistry–Methods},

volume = {6},

issue = {9},

abstract = {Transforming chemically complex waste streams into high-performance calcium–manganese oxide multivalent nanocomposites (MNC) provides a promising route toward circular and sustainable materials engineering. Here, we report the synthesis of compositionally tunable Ca–Mn MNC derived entirely from waste eggshells and spent alkaline batteries through hydrothermal processing. In situ X-ray diffraction (XRD) revealed strongly composition-dependent thermal phase evolution, with Ca:Mn = 25:75 sample stabilizing mixed-valence Mn oxide phases with cubic CaMn_{7}O_{12} quadruple perovskite phases while Ca:Mn = 75:25 sample was dominated by highly crystalline CaO phases. STEM-EELS and XPS analyses demonstrated substantial heterogeneity of Mn valence between the 25CaMn and 50CaMn catalysts, confirming the coexistence of Mn^{2+}, Mn^{3+}, and Mn^{4+}-type environments through spatial variation in the Mn L_{3}/L_{2} ratio associated with 3\textit{d} electronic transitions. Among the investigated compositions, 25CaMn exhibited a CO_{2} space–time yield (STY) of 57 mmol_{CO_{2}}.g^{−1}_{cat}.h^{−1} and achieved ∼85% CO conversion near 300 °C, whereas 50CaMn delivered the highest overall CO_{2} productivity with a maximum STY of 60 mmol_{CO_{2}}.g^{−1}_{cat}.h^{−1} between 350 and 400 °C. Excessive Ca incorporation in 75CaMn suppressed Mn lattice participation and lowered catalytic activity at intermediate temperatures. This work demonstrates how waste-derived precursor engineering can generate multivalent electronic structure and catalytic functionality.},

keywords = {P08},

pubstate = {published},

tppubtype = {article}

}

@article{Zhu_2026a,

title = {Emergent ferroelectric order in strained KTaO_{3} by anharmonic and machine learned force fields methods},

author = {Yu Zhu and Luigi Ranalli and Taikang Chen and Wei Ren and Cesare Franchini},

doi = {10.1103/8jph-2w9q},

year  = {2026},

date = {2026-07-06},

journal = {Physical Review Materials},

volume = {10},

pages = {074403},

abstract = {Ferroelectric materials are a class of dielectrics that exhibit spontaneous polarization which can be reversed under an external electric field. The emergence of ferroelectric order in incipient ferroelectrics is a topic of considerable interest from both fundamental and applied perspectives. Despite evidence from first-principles calculations that strain triggers ferroelectricity in KTaO_{3}, conventional methods cannot reliably characterize the soft-mode dynamics that govern its ferroelectric behavior. In this study, we investigate the impact of in-plane uniaxial and biaxial strain, ranging from 0 to 1%, on pristine KTaO_{3} to explore its potential for ferroelectricity induction via inversion symmetry breaking. By integrating density-functional theory calculations with the stochastic self-consistent harmonic approximation assisted by on-the-fly machine learned force fields, we obtain accurate structural information and dynamical properties under varying strain conditions while incorporating higher-order anharmonic effects. Employing the Berry-phase method, we obtained the ferroelectric polarization of the strained structures over the entire temperature range up to 300 K. Our findings provide valuable insights into the role of strain in stabilizing ferroelectricity in KTaO_{3}, offering guidance for future experimental and theoretical studies on strain-engineered ferroelectric materials.},

keywords = {P07},

pubstate = {published},

tppubtype = {article}

}

@article{CanoBlanco_2026b,

title = {Cooperative Redox Catalysis of N_{2}O Decomposition by Short-Range RhO_{x} and CeO_{x} Anchored to Co_{3}O_{4}},

author = {Daniel C. Cano-Blanco and Silvio Bellomi and Daniele Bonavia and Ivo Alxneit and Kirill A. Lomachenko and Karin Föttinger and Oliver Kröcher and Davide Ferri},

doi = {10.1002/anie.7890563},

year  = {2026},

date = {2026-06-23},

urldate = {2026-06-23},

journal = {Angewandte Chemie International Edition},

volume = {65},

number = {34},

pages = {e7890563},

abstract = {Hybrid materials based upon mixed metal oxides provide an effective strategy to boost catalytic performance through redox-induced interfacial engineering. Herein, we present an efficient catalyst toward N_{2}O decomposition containing short-range ordered RhO_{x} and CeO_{x} species anchored to the Co_{3}O_{4} spinel. The activity enhancement relative to Co_{3}O_{4} is non-additive with respect to the RhO_{x}/Co_{3}O_{4} and CeO_{x}/Co_{3}O_{4} interfaces and is uniquely linked to the modulation of the Co and Rh oxidation states at a synergistic Rh–O–Co–O–Ce interface. This ensemble provides increased redox flexibility and facilitated lattice oxygen activation, resulting in markedly enhanced N_{2}O decomposition. Kinetic analysis and operando modulated excitation x-ray absorption spectroscopy (ME-XAS) provide direct mechanistic evidence that N_{2}O decomposition proceeds via a multi-site, cooperative Mars-van Krevelen pathway, in which Co_{3}O_{4}–CeO_{2} acts as an oxygen reservoir enabling the redox cycling of RhO_{x} species. This study highlights the ability of mixed metal oxide catalysts to exploit interfacial effects to achieve improved activity in redox-mediated reactions and offers a rationale for the engineering of metal oxide–metal oxide catalysts guided by operando spectroscopy.},

keywords = {P10},

pubstate = {published},

tppubtype = {article}

}

@article{Schmiedmayer_2026a,

title = {Scalar machine learning of tensorial quantities—Born effective charges from monopole models},

author = {Bernhard Schmiedmayer and Angela Rittsteuer and Tobias Hilpert and Georg Kresse},

doi = {10.1063/5.0327083},

year  = {2026},

date = {2026-06-23},

journal = {The Journal of Chemical Physics},

volume = {164},

pages = {244114},

abstract = {Predicting tensorial properties with machine learning models typically requires carefully designed tensorial descriptors. In this work, we introduce an alternative strategy for learning tensorial quantities based on scalar descriptors. We apply this approach to the Born effective charge tensor, showing that scalar (monopole) kernel models can successfully capture its tensorial nature by exploiting the definition of the Born effective charge tensor as the derivative of the polarization with respect to atomic displacements. We compare this method with tensorial (dipole) kernel models, as established in our previous work, in which the tensorial structure of the Born effective charge is encoded directly in the kernel and obtained via its derivative. Both approaches are then used for charge partitioning, enabling the separation of monopole and dipole contributions. Finally, we demonstrate the effectiveness of the framework by computing finite-temperature infrared spectra for a range of complex materials.},

keywords = {P03},

pubstate = {published},

tppubtype = {article}

}

@article{Hammer_2026a,

title = {When surface dynamics fakes symmetry: Oxygen on Rh(100) revisited},

author = {Lutz Hammer and Tilman Kißlinger and Margareta Wagner and Reinhard B. Neder and Michael Schmid and Ulrike Diebold and M. Alexander Schneider},

doi = {10.1103/5wmb-kmjb},

year  = {2026},

date = {2026-06-15},

journal = {Physical Review Research},

volume = {8},

pages = {023296},

abstract = {Heating a long-range ordered adsorbate phase beyond its stability temperature does not necessarily result in a disordered phase; it can also break up into heavily fluctuating ordered domains. Temporal and/or spatial averaging over these fluctuations may give the impression of both a wrong periodicity and false symmetry elements such as nonexisting glide planes or rotational axes of incorrect order. This can happen in real space and reciprocal space, and also below liquid-nitrogen temperature, so that the true nature of the phase might remain undetected. We demonstrate this scenario at the catalytically active Rh(100) surface covered by 1/2 monolayer of oxygen, using quantitative low-energy electron diffraction, variable-temperature scanning tunneling microscopy, and density functional theory. Using the example of CO adsorption, we show that local symmetry can have a decisive influence on the binding energy and thus the chemical reactivity.},

keywords = {P02},

pubstate = {published},

tppubtype = {article}

}

@article{Alves_2026a,

title = {Few-layer MoS_{2} dispersion induced by sulfur atom sharing to promote CO_{2} hydrogenation to methanol},

author = {Gustavo A. S. Alves and Silvio Bellomi and Tobias Wagner and Alberto Tampieri and Christian Etzlstorfer and Michael Stöger-Pollach and Daniel C. Cano-Blanco and Karin Föttinger},

doi = {10.1039/d6ta01545j},

year  = {2026},

date = {2026-06-05},

urldate = {2026-06-05},

journal = {Journal of Materials Chemistry A},

volume = {14},

number = {44},

pages = {29662-29671},

abstract = {With the ongoing interest in developing more stable and versatile catalysts for CO_{2} hydrogenation to methanol, molybdenum sulfide (MoS_{2}) has been recently proposed as an alternative material. However, in its bulk state, CO_{2} hydrogenation over MoS_{2} typically favors methane formation. In this work, a wet impregnation method is applied for the production of ZnS-supported MoS_{2}, as confirmed by characterization via X-ray Diffraction, Raman and X-ray Photoelectron Spectroscopy. In contrast with the negligible methanol production shown by the pure MoS_{2} reference, 2% MoS_{2}/ZnS presents a methanol selectivity of 78% at a CO_{2} conversion of 2.3% under the mild reaction conditions of 200 °C and 20 bar. Density Functional Theory and Transmission Electron Microscopy suggest that the improved catalytic activity arises from an even dispersion of few-layer MoS_{2} with exposed basal plane sites at the ZnS surface, an arrangement possibly enabled by the structural similarity and the shared S atoms between 2H-MoS_{2} and W–ZnS phases. This hypothesis is strengthened by the comparison with the reference sample consisting of ZrO_{2}-supported MoS_{2} sample, in which more agglomerated MoS_{2} particles resulted in a lower and less selective methanol production. Moreover, in situ X-ray absorption spectroscopy and H_{2} temperature-programmed reduction suggest further evidence of a MoS_{2}/ZnS interaction during the H_{2} pretreatment, which may promote not only the expected formation of S-vacancies but also a partial reconstruction of MoS_{2} given the close contact and sharing of S atoms with the ZnS support.},

keywords = {P10},

pubstate = {published},

tppubtype = {article}

}