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Item type:Publication, Access status: with files , Simultaneous learning of static and dynamic charges(Royal Society of Chemistry (RSC), 2026-06-01); ; ; Long-range interactions and electric response are essential for accurate modeling of condensed-phase systems, but capturing them efficiently remains a challenge for atomistic machine learning. Traditionally, these two phenomena can be represented by static charges that underlie Coulomb interactions between atoms, and dynamic charges such as atomic polar tensors—aka Born effective charges—describing the response to an external electric field. We critically compare different approaches to learn both types of charges within a single model architecture, taking bulk water and water clusters as paradigmatic examples: (1) learning them independently; (2) coupling static and dynamic charges based on their physical relationship with a single global coupling constant to account for dielectric screening; (3) coupled learning with a local, environment-dependent screening factor. In the coupled case, correcting for dielectric screening is essential, yet the common assumption of homogeneous, isotropic screening breaks down in heterogeneous systems such as water clusters. A learned, environment-dependent screening restores high accuracy for the dynamic charges. However, the accuracy gain over independent dynamic predictions is negligible, while the computational cost increases compared to using separate models for static and dynamic charges. This suggests that, despite the formal connection between the two charge types, modeling them independently is the more practical choice for both condensed-phase and isolated cluster systems.Publicationtype: Journal Article109 46 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Temperature-dependent capacitance of the electrical double layerWe use atomistic simulations to study the electrical double layer (EDL) at an electrode–electrolyte interface at different temperatures. For a constrained electrode charge, the potential drop over the EDL increases with temperature, a phenomenon known as the thermal voltage rise (TVR). Prior continuum models attributed TVR to expansion of the EDL with increasing temperature; conversely, our simulations with aqueous, organic, and ionic liquids show that the EDL does not expand but that the TVR is caused by a decrease in interfacial permittivity with increasing temperatures.Publicationtype: Journal Article57 62 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Static dielectric permittivity profiles and coarse-graining approaches for water in graphene slit pores(AIP Publishing, 2026-03-27); ; ; ; The dielectric response of nano-confined fluids is important for a wide range of technologies and biological systems, ranging from the fundamentals of energy storage to the stability of lipid membrane bilayers. Its calculation from molecular simulations has become a viable tool since the 2010s and is often employed to rationalize experimental observations. However, confusion has emerged on the underlying boundary conditions, and correspondingly, the concept of dielectric profiles is often misunderstood in the literature. Here, we re-derive the Green–Kubo relation for the linear dielectric response profile of fluids in planar confinement, while carefully considering the different underlying boundary conditions; if the latter are correctly accounted for, profiles from equilibrium simulations are perfectly in line with results using externally applied fields. We discuss possible pitfalls and address misunderstandings, regarding both the detailed calculation and the general concept of dielectric profiles, as well as procedures to coarse-grain the microscopic dielectric behavior in order to connect to experimental observables. Simulations consistently reveal that the dielectric response of water is bulk-like down to confining scales as small as ∼1 nm. However, the effective dielectric response of confined systems, which determines their capacitance, depends on the precise location of the dielectric interface. Using concepts from effective medium theory, we show that the long-range reduction of the effective dielectric response, reported in both experimental and theoretical studies, is in line with a dielectric response that reaches the bulk value at about 1 nm from the surface. The effective dielectric response can be interpreted in terms of the commonly employed concept of an interfacial capacitance. We find that the dielectric properties of simulated water are independent of the simulation details and the water model employed, thus revealing the universal properties of water polarization correlations.Publicationtype: Journal Article4 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Phase diagram and criticality of the modified primitive electrolyte model in bulk and in inert and conducting confinementIonic fluids under conductive confinement are central to technologies such as batteries, supercapacitors, and fuel cells. Their interfacial behavior governs energy storage and electrochemical processes. Despite their importance, the thermodynamics of even simple models-such as the charged Lennard-Jones fluid-remain underexplored in this regime. We present an extended Wang-Landau sampling approach to efficiently compute the density of states of charged mixtures with respect to the particle number. The method supports simulations in both bulk and confined geometries. Combined with the constant potential method, it also enables the study of effects due to confining electrodes. We employ this approach to study symmetric, binary mixtures of charged Lennard-Jones particles-the modified restricted primitive model-in bulk, in inert confinement, and in conductive confinement at the potential of zero charge. Our results show that confinement shifts the vapor-liquid critical point to lower temperatures and higher densities compared to bulk, in line with the classical concept of capillary condensation. Importantly, conductive boundaries significantly lower the chemical potential of coexistence relative to inert confinement. For both confinement types, we find a minimal pore size below which no phase transition occurs, corresponding to a super-critical fluid. These findings offer deeper insight into the phase behavior of ionic fluids in energy-relevant porous environments.Publicationtype: Journal Article14 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Interfacial ion hydration and electrostatics govern salt precipitation and crystal morphology(2025-12-28); ; ; Salt precipitation, a phenomenon central to processes such as soil salinization, water treatment, and energy storage, is dictated by nanoscale hydration and electrostatic interactions at crystal interfaces. Understanding how their interplay gives rise to salt-specific growth behaviors and morphologies remains a critical challenge. Combining large-scale molecular dynamics simulations with free energy calculations, we investigate the precipitation behavior of three common salts, namely, NaCl, KCl, and Na2SO4, on their respective crystal surfaces. While all crystals grow steadily under controlled supersaturation, their surface morphologies differ markedly. KCl grows in a nearly ideal layer-by-layer mode, whereas NaCl and Na2SO4 develop increasingly rough, defect-rich surfaces. This roughening is accompanied by an early-stage charge imbalance at the crystal surface, characterized by preferential cation adsorption. The resulting local electrostatic environment modifies the structuring and dynamics of interfacial water, which in turn facilitates the premature growth of subsequent layers. We further find that ion adsorption is strongly defect-dependent: kinks provide stabilizing environments, whereas steps are energetically unfavorable due to their distinct hydration. Our study offers molecular-level insight into the coupled roles of ion-specific adsorption and interfacial hydration in shaping crystal morphology for different salts.Publicationtype: Journal Article61 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , A lattice Boltzmann approach for modeling coupled evaporation/precipitation processes in porous media(ESS Open Archive, 2025-11-06); ; We present a novel numerical approach for simulating coupled evaporation and salt precipitation processes in porous media using the lattice Boltzmann method. Our model combines a Shan-Chen multiphase flow framework with a volume-based discretization method for diffusing salt species, where the coupling mechanism operates through solvation energy differences. The framework incorporates a precipitation model based on first-order reaction kinetics, enabling the transformation of fluid cells into solid crystal cells upon reaching threshold concentrations. We verify our model against analytical solutions for crystal growth and evaporation rates, demonstrating excellent agreement. The model is then applied to investigate the influence of wetting properties on evaporation and salt precipitation in porous media. Our simulations reveal that the wettability of both the porous medium and the precipitated salt crystals has a significant impact on precipitation patterns and pore clogging. Notably, increased salt crystal wettability promotes more effective pore blocking, substantially reducing permeability and evaporation rates. We find that the slowest evaporation occurs when salt crystals have high wettability, while the porous medium exhibits lower wettability because this configuration maximizes pore clogging. This work presents a novel framework to gain insight into the intricate interplay between fluid dynamics, wetting properties, and salt precipitation in porous media, with implications for understanding soil salinization, building material degradation, and the formation of geological salt crusts.Publicationtype: Preprint33 24 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Intermittent molecular motion and first passage statistics for the NMR relaxation of confined waterThe structure and dynamics of fluids confined in nanoporous media differ from those in bulk, which can be probed using NMR relaxation measurements. We here show, using atomistic molecular dynamics simulations of water in a slit nanopore, that the behavior of the NMR relaxation rate, R_{1}, with varying surface interaction and confinement strength can be estimated from the exchange statistics of fluid molecules between the adsorbed surface layer and the bulk region. In detail, we test the applicability of intermittent molecular water dynamics, a theoretical framework that relates NMR relaxation to the statistics of molecular exchange between these two states. We confront this framework with the direct evaluation of dipolar NMR relaxation rates from atomistic molecular dynamics simulations of water confined in a slit nanopore, allowing to assess its accuracy across varying surface interactions. We employ first return passage time calculations to quantify the molecular exchange statistics, thereby linking microscopic parameters of the confined fluid-such as adsorption time, pore size, and diffusion coefficient-to the NMR relaxation rate. Our results show that the theoretical framework proposed by Levitz et al. captures the qualitative trends of NMR relaxation rates observed in our molecular simulations. This approach allows to predict, interpret, and analyze the molecular relaxation of fluids at interfaces using merely concepts of statistical mechanics that can be generalized to closed and open geometries and thus yields direct insights into the experimental study of NMR relaxation with varying surface chemistry or confinement strength.Publicationtype: Journal Article29 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Theory and modeling of transport for simple fluids in nanoporous materials: from microscopic to coarse-grained descriptions(American Chemical Society (ACS), 2025-02-18); ; We present the state-of-the-art of theoretical modeling, molecular simulation, and coarse-graining strategies for the transport of gases and liquids in nanoporous materials (pore size 1-100 nm). Special emphasis is placed on the transport of small molecules in zeolites, active carbons, metal-organic frameworks, but also in nanoporous materials with larger pores such as ordered and disordered mesoporous oxides. We present different atomistic and mesoscopic methods as well as available theoretical formalisms to describe such a complex problem. Attention is given to the investigation of different molecular transport coefficients─including the self, collective and transport diffusivities─but also to the determination of free energy barriers and their role in overall adsorption/separation process rates. We further introduce other available approaches such as hierarchical simulations and upscaling strategies. This review focuses on simple fluids in prototypical nanoporous materials. While the phenomena covered here capture the main physical mechanisms in such systems, complex molecules will exhibit additional specific features. For the sake of clarity and brevity, we also omit multicomponent systems (e.g., fluid mixtures, electrolytes, etc.) and electrokinetic effects arising when charged systems are considered (ionic species, charged surfaces, etc.), both of which add to the complexity.Publicationtype: Review Article49