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Structure–transport relations for Li+ ions at the electrolyte/polymer interface from classical molecular dynamics
Lithium-ion batteries have become indispensable in modern life due to their ability to provide efficient and reliable energy. While extensive research has been conducted on electrolyte behavior at electrode interfaces, the electrolyte/separator interface and the transport properties through it remain relatively unexplored. Yet, optimizing the transport mechanism could improve power density and reduce overheating. Lithium ions diffuse through the pore space in the separator, where an extensive interfacial surface area is in contact with the electrolyte. Experimental studies suggest that separator–electrolyte interactions may impact the surface chemistry and microscopic behavior of transport processes, but atomic-level insights are still lacking. This study uses classical molecular dynamics simulations to investigate the behavior of 1.2M LiPF6 in ethylene carbonate at the interface with a polyethylene substrate, a commonly used separator material. Our simulations reveal how the solvation structure and diffusive mechanisms change within thin interfacial films as a function of the distance from the polyethylene substrate. The results could provide a benchmark for engineering future electrolytes and separator materials to eventually control transport properties.
A research database for experimental electrocatalysis: Advancing data sharing and reusability
The availability of high-fidelity catalysis data is essential for training machine learning models to advance catalyst discovery. Furthermore, the sharing of data is crucial to ensure the comparability of scientific results. In electrocatalysis, where complex experimental conditions and measurement uncertainties pose unique challenges, structured data collection and sharing are critical to improving reproducibility and enabling robust model development. Addressing these challenges requires standardized approaches to data collection, metadata inclusion, and accessibility. To support this effort, we have developed an extensive data infrastructure that curates and organizes multimodal data from electrocatalysis experiments, making them openly available through the catalysis-hub.org platform. Our datasets, comprising 241 experimental entries, provide detailed information on reaction conditions, material properties, and performance metrics, ensuring transparency and interoperability. By structuring electrocatalysis data in web-based as well as machine-readable formats, we aim to bridge the gap between experimental and computational research, allowing for improved benchmarking and predictive modeling. This work highlights the importance of well-structured, accessible data in overcoming reproducibility challenges and advancing machine learning applications in catalysis. The framework we present lays the foundation for future data-driven research in electrocatalysis and offers a scalable model for other experimental disciplines.
Bingel–Hirsch reaction on actinidofullerene U@<i>C</i>2v(9)-C82: Improved regioselectivity compared to lanthanide counterpart
Actinidofullerenes constitute a family of fullerenes that exhibit different metal–cage interactions, electronic structures, and properties compared to lanthanidofullerenes. In this study, we investigate the reactivity of mono-uranofullerene U@C2v(9)-C82 under the Bingel–Hirsch reaction and observe significantly higher regioselectivity, along with other differences in the reaction products, compared to La@C2v(9)-C82. Two products are obtained: a cycloadduct, which is the most abundant and has been characterized by x-ray crystallography, and a minor regioisomer that is most likely a single-bond product. Density functional theory calculations can explain the experimental structure and the formation of the two products and indicate that uranium is formally U(III) in both of them. The most abundant cycloadduct is formed under kinetic control, as found for other Bingel–Hirsch adducts, whereas the single-bond product is formed after oxidation of the anionic intermediate of the conventional Bingel–Hirsch reaction. This work is a new example of the unique reactivity and chemical properties of actinidofullerenes, which arise from their distinctive actinide–fullerene interactions.
Static disorder-induced renormalization of polariton group velocity
Molecular exciton-polaritons exhibit long-range, ultrafast propagation, yet recent experiments have reported far slower propagation than expected. In this work, we implement a nonperturbative approach to quantify how static energetic disorder renormalizes polariton group velocity in strongly coupled microcavities. The method requires no exact diagonalization or master equation propagation and depends only on measurable parameters: the mean exciton energy and its probability distribution, the microcavity dispersion, and the Rabi splitting. Using parameters corresponding to recently probed organic microcavities, we show that exciton inhomogeneous broadening slows both lower and upper polaritons, particularly when the mean exciton energy fluctuation approaches the collective light–matter coupling strength. A detailed discussion and interpretation of these results is provided using perturbation theory in the limit of weak resonance scattering. The magnitude of the effects examined in this work supports the conclusion that most of the reported polaritonic slowdown arises from dynamical (phonon-assisted) disorder, with static energetic disorder contributing only secondarily.
Evaluating non-equilibrium trajectories via mean back relaxation: Dependence on length and time scales
The mean back relaxation (MBR) relates the value of a stochastic process at three different time points. It has been shown to detect broken detailed balance under certain conditions. For experiments of probe particles in living and passivated cells, MBR was found to be related to the so-called effective energy, which quantifies the violation of the fluctuation–dissipation theorem. In this paper, we discuss the dependence on the length and time parameters that enter MBR, both for cells as well as for a model system, finding qualitative agreement between the two. For the cell data, we extend the phenomenological relation between MBR and effective energy to a larger range of time parameters compared to previous work, allowing us to test it in systems with limited resolution. We analyze the variance of back relaxation (VBR) in dependence of the mentioned parameters, relevant for the statistical error in MBR evaluation. For Gaussian systems, the variance is found analytically in terms of the mean squared displacement, and we determine its absolute minimum as a function of the length and time parameters. Comparing VBR from cell data to a Gaussian prediction demonstrates a non-Gaussian process.
Laser induced fluorescence spectroscopy of the jet-cooled SiNSi radical: Rotational analyses of the C̃2Δu−X̃2Πg transition and vibronic analysis in the C̃2Δu state
We have generated SiNSi in supersonic free jet expansions and measured laser induced fluorescence (LIF) spectra in the ultraviolet region. On the basis of rotational analyses, nine vibronic bands in the LIF spectra have been attributed to the C̃Δu2 – X̃Πg2 electronic transition of SiNSi. The 32 393 and 32 505 cm−1 subbands have been assigned to the two spin components of the 000 band. In addition, the C̃ (0220) μΣu(+)2 –, (0200) Δu2 –, (0220) κΣu(−)2 –, (1000) Δu2 –, (0420) μΣu(+)2 –, (040,40) μΔu2 –, (0620)μΣu(+)2 –, and (1620)μΣu(+)2 – X̃(0000)Πg2 bands have been identified. The experimental identification that the Σu(+)2 level is lower than Σu(−)2 suggests that the in-phase bending potential, labeled as V+, is the lower (or outer) one for the C̃Δu2 electronic state. The Δl = ±2 vibronic bands, such as C̃ (0220) Σu(+)2 – X̃(0000)Πg2, which are forbidden by the Δl = 0 selection rule, are induced by the (quadratic) Renner–Teller (R–T) interaction of the C̃Δu2 state with the ẼΣu+2 state, i.e., the vibronic transition moment is induced by the quadratic R–T (2RT) interaction of the C̃Δu2 state with the ẼΣu+2 state. The vibronic bands can also obtain their transition moments through their neighbors, which are the vibronic bands of the electronically forbidden D̃Σg+2 – X̃Πg2 transition. Based on the theory of the quaternary R–T (4RT) interaction, the vibrational structure of the C̃Δu2 state has been analyzed, and a local perturbation between the C̃(02l0) levels and their neighbor, D̃(0110)Πu2, has been identified. The observations suggest that, although the direct couplings between the C̃Δu2 and D̃Σg+2 states are negligible, their indirect couplings through the other states are effective.
Toward a formulation of a CISS theory with the inclusion of two-particle relativistic effects, electron–phonon coupling, and electron–electron correlation. An application to NMR-based chiral discrimination
The current status of the theoretical foundations of the Chiral-Induced Spin Selectivity (CISS) effect has substantially improved from its original one-electron formulation. However, there is a need to improve the inclusion of electron–vibrational interaction, the exchange and correlation effects arising from electron–electron interactions, and non-Born–Oppenheimer coupling to enhance the predictive power of the theory and its agreement with experiments. In an attempt to overcome these difficulties, we advance in the present work a microscopic quantum mechanical treatment of CISS based on the relativistic Breit–Pauli many-particle Hamiltonian. In particular, we determine in this context the effect that including non-Born–Oppenheimer components arising in a Taylor expansion of the electron–nuclear potential has on the spin–orbit coupling term of this Hamiltonian. We also consider in this framework the electron–electron exchange and correlation effects and propose some practical approximations based on non-relativistic approaches. Finally, we extend the application of the Breit–Pauli Hamiltonian to describe nuclear–nuclear spin interactions and discuss the possibility of explaining enantiomeric selectivity in cross-polarization nuclear magnetic resonance experiments.
Transient vibrational dynamics unveils the intricate mechanism of ultrafast photorelaxation in a molecular rotor
We investigate the excited-state vibrational dynamics of the second-generation molecular rotor 9-(2-methyl-2,3-dihydro-1H-cyclopenta[a]naphthalen-1-ylidene)-9H-fluorene using an integrated theoretical–computational approach. Our methodology combines ab initio molecular dynamics with time-dependent density functional theory and a polarizable continuum model to characterize the ground- and excited-state potential energy surfaces of the rotor in cyclohexane. Time-resolved vibrational analysis based on wavelet transform enables the decomposition of the nuclear motion into time–frequency components. This approach allows us to follow the evolution of vibrational dynamics and their role in key relaxation pathways and spectroscopic signals. We propose that, although not directly observable, complex vibrational dynamics influence the emission by modulating both the transition energy and the emission dipole moment. These include C=C stretching, out-of-plane motions at the axle carbon, and rotor–stator torsional modes. For the first time, we assign and interpret low-frequency modes observed experimentally at ∼180 cm−1 in time-resolved fluorescence. We reproduce the extent and the dynamics of the pronounced red shift of the C=C stretching mode upon excitation, as observed in the femtosecond stimulated Raman spectrum (1585 cm−1 in the ground state vs 1350–1440 cm−1 in the excited state). Regarding the photoisomerization, we identify a clear correlated steric-relief mechanism of the two main relaxation coordinates: torsion about the C=C axle and pyramidalization at the stator–bridge carbon. This study demonstrates the power of transient vibrational analysis in unraveling complex photorelaxation mechanisms by establishing a direct link between experimental data and excited-state molecular dynamics simulations.
A theoretical framework for investigating the role of heterogeneity of extensibility in structure and dynamics of flexible polymer
Heteropolymers are ubiquitous in both synthetic systems, such as block copolymers, and biological macromolecules, including proteins and nucleic acids. Beyond their chemical composition, these polymers often exhibit spatial variations in physical properties. For instance, in biopolymers such as chromatin, the heterogeneity of extensibility arises from inherent molecular features as well as extensile or contractile active forces. In this article, we develop a theoretical framework that extends the physics of flexible polymers, a widely used tool for describing biopolymer dynamics, to incorporate spatially varying extensibility. Using this approach, we specifically analyze the structure and dynamics of flexible heteropolymers with periodic stepwise extensibility profiles. We find that this heterogeneity leads to qualitative deviations in dynamical observables, such as mean squared displacement, while also increasing structural anisotropy. Altogether, this framework provides a platform for interpreting heterogeneous extensibility from experimental data, especially for biopolymers, as well as for designing heteropolymers with tailored structural and dynamic properties.
Conformational sampling of seven-membered rings using extended puckering collective variables in metadynamics
Seven-membered rings, though scarce in biosynthetic pathways, are increasingly recognized as conformationally rich scaffolds for engineered enzymes and drug leads. Accurately capturing their flexibility requires the use of enhanced-sampling methods. Here we present a set of collective variables (CVs) for metadynamics simulations that extend the Cremer–Pople puckering coordinates to seven-membered rings, and we validate them on cycloheptane and other molecules of increasing complexity (buxenine-G, two azepane derivatives, and ε-caprolactone). The new CVs can be used directly in PLUMED—a popular open-source library for enhanced-sampling and free-energy methods—so they can be used directly in metadynamics workflows. They allow the investigation of conformational transitions, the identification of metastable states, and the mapping of free-energy landscapes of any seven-membered-ring molecule. This provides a quantitative framework for probing the conformational behavior of flexible seven-membered scaffolds and will aid in the rational design of conformationally locked substrates for enzyme engineering and related applications.
Evaluating the use of a machine learning simulator for structure–property prediction: A case study on disordered elastic networks
Machine learning models often require large datasets and struggle to generalize beyond their training distribution. These limitations pose significant challenges in scientific and engineering contexts, where generating exhaustive datasets is often impractical and the goal is to frequently discover novel solutions outside the training domain. In this work, we explore the use of dynamical data through a graph neural network-based simulator to enable efficient system-to-property learning and out-of-distribution prediction in the context of uniaxial compression of two-dimensional disordered elastic networks. We find that the simulator can learn the underlying physical dynamics from a small number of training examples and accurately reproduce the temporal evolution of unseen networks. Notably, the simulator is able to accurately predict emergent properties such as Poisson’s ratio and its dependence on strain, even though it was not explicitly trained for this task. In addition, it generalizes well across variations in system temperature, strain amplitude, and most significantly, Poisson’s ratios beyond the training range. These findings suggest that using dynamical data to train machine learning models can support more information efficient and generalizable approaches for materials and molecular design, especially in data-scarce settings.
Laser induced fluorescence spectroscopy of the jet-cooled SiNSi radical: Vibrational analysis of the X̃Πg2 state
We have generated SiNSi in supersonic free expansions and observed laser induced fluorescence (LIF) in the ultraviolet (UV) and visible regions. We measured two kinds of LIF excitation spectra from the X̃Πg2 electronic state: one detecting UV fluorescence and the other detecting visible fluorescence. By exciting the vibronic bands observed in the LIF excitation spectra, we recorded dispersed fluorescence (DF) spectra from the single vibronic levels to the X̃Πg2 state. The vibrational structures of the DF spectra are complicated due to the relatively large vibronic interactions in the X̃Πg2 state. We were not able to analyze the structure using regular formulations derived from perturbational treatments that consider the Renner–Teller (R–T) and spin–orbit (SO) couplings and the anharmonicity of the ν2 bending potential. Instead, we analyzed it by directly diagonalizing the vibronic Hamiltonian, including not only R–T, SO, and the anharmonicity but also Fermi resonance between the ν1 symmetric stretching and ν2 modes and anharmonicities, x11 and x12. The vibronic analysis revealed two characteristics: a relatively large R–T parameter, ϵ = +0.51, and a SO constant close to the bending frequency, A ≈ 0.8ω2. Both these characteristics bring about accidental proximity of the vibronic levels in the D∞h system, and this proximity causes heavy mixing among the vibronic levels. The results can be applied to find weak vibrationally hot bands in the rotationally resolved LIF excitation spectra observed, and actually the Q1p band head of the hot band, C̃(0110)Πg2 − X̃(0110)κΣg(+)2, has been able to be assigned. The band head assignment suggests an accuracy of a few cm−1 for the present vibronic analysis of the DF spectra, with a peak accuracy of ±3 cm−1.
1D transition metal oxide chains as a challenging model for <i>ab initio</i> calculations
Providing highly simplified models of strongly correlated electronic systems that challenge ab initio calculations can serve as a valuable testing ground to improve these methods. In this study, we present a comprehensive investigation of the structural, magnetic, and electronic properties of one-dimensional transition metal mono-oxide chains (VO, CrO, MnO, FeO, CoO, and NiO) using density functional theory (DFT), DFT+U, and coupled-cluster singles and doubles (CCSD) calculations. The Hubbard U parameter for DFT+U is determined using linear response theory. In all systems studied except MnO, the presence of multiple local minima—primarily due to the electronic degrees of freedom associated with the d-orbitals—leads to significant challenges for DFT, DFT+U, and Hartree–Fock methods in finding the global minimum in ab initio calculations. Our results indicate that the antiferromagnetic (AFM) state is energetically favored for all chains, except CrO, when using DFT+U and the Perdew–Burke–Ernzerhof (PBE) functional. Analysis of the band structures shows that while PBE often predicts metallic or half-metallic FM states, DFT+U opens band gaps and correctly yields insulating behavior in all cases. Furthermore, we compared the energy differences between the AFM and FM states using DFT+U and CCSD for CrO, MnO, FeO, CoO, and NiO. Our findings indicate that CCSD predicts larger energy differences in some cases compared to DFT+U, suggesting that the Hubbard U parameter obtained through linear response theory may be overestimated when used to calculate energy differences between different magnetic states. For CrO, CCSD predicts an AFM ground state, in contrast to the predictions from DFT+U and PBE methods.
Quantum dynamics at conical intersections in solution. II. Multiconfigurational wavefunction dynamics at finite temperature
The multiplicative neural network (m-NN) potentials described in Paper I [Błasiak et al., J. Chem. Phys. 163, 124108 (2025)] are employed to carry out multi-layer multi-configuration time-dependent Hartree simulations of the dynamics at a conical intersection including environmental effects. For a model of cis–trans isomerization in a protonated Schiff base, vibronic effects induced by intramolecular torsional and bond-length-alternation modes act concertedly with a collective environmental mode, which plays the role of an effective tuning mode. The latter is coupled to a residual environment, and the combination of the effective and residual modes conforms to an overdamped Brownian oscillator type spectral density. Thermal averages are included by the thermofield dynamics approach, in line with the thermal Hamiltonian developed in Paper I. The m-NN potentials, modeled according to the regularized diabatic states representation, permit an accurate representation of the vibronic coupling Hamiltonian beyond a linear vibronic coupling model. The initial excited-state dynamics is determined by the approach to a curved conical intersection seam, followed by a strongly dissipative phase leading to equilibration in the adiabatic ground state. The characteristic inertial time scale of the environment impacts not only the time of approach to the conical intersection seam but also the isomerization yield. The present study makes first steps toward extending the m-NN approach to a treatment of collective environmental non-equilibrium evolution on par with intramolecular excited-state nonadiabatic dynamics.
Quantum dynamics at conical intersections in solution. I. Multiplicative neural networks and thermofields
Environmental effects on the vibronic dynamics at a conical intersection can be captured by collective modes, which affect both the topology of the nonadiabatically coupled potential surfaces and the transient dynamics. Here, we show how neural network (NN) potentials can be adapted to a combination of intramolecular coordinates and collective environmental modes. Specifically, we use multiplicative NN (m-NN) potentials, which are fitted to a diabatic representation of regularized diabatic states type. These potentials are readily combined with multiconfigurational wave functions for high-dimensional quantum dynamics. The thermofield dynamics (TFD) approach is employed to include thermal averaging at the wave function level, and we formulate a thermal NN/TFD Hamiltonian that accommodates initial vibronic correlations and collective/residual-mode coupling in the environmental subspace. For a model system describing the isomerization of protonated Schiff bases in solution, the solvent is represented by an overdamped Brownian-oscillator spectral density. In a companion paper [B. Błasiak et al., J. Chem. Phys. 163, 124109 (2025)], the resulting m-NN/TFD Hamiltonian is employed in real-time quantum dynamical simulations using the multi-layer multiconfiguration time-dependent Hartree method.
Continuous-time multifarious systems. I. Equilibrium multifarious self-assembly
Multifarious assembly models consider multiple structures assembled from a shared set of components, reflecting the efficient usage of components in biological self-assembly. These models are subject to a high-dimensional parameter space, with only a finite region of parameter space giving reliable self-assembly. Here, we use a continuous-time Gillespie simulation method to study multifarious self-assembly and find that the region of parameter space in which reliable self-assembly can be achieved is smaller than what was obtained previously using a discrete-time Monte Carlo simulation method. We explain this discrepancy through a detailed analysis of the stability of assembled structures against chimera formation. We find that our continuous-time simulations of multifarious self-assembly can expose this instability in large systems even at moderate simulation times. In contrast, discrete-time simulations are slow to show this instability, particularly for large system sizes. For the remaining state space, we find good agreement between the predictions of continuous- and discrete-time simulations. We present physical arguments that can help us predict the state boundaries in the parameter space and gain a deeper understanding of multifarious self-assembly.
Line shapes in pump–probe spectroscopy of polaritons
Forming new hybrid quasiparticles by strong light–matter coupling is a promising tool for tailoring the photophysics and photochemistry of molecules. Thus, the ultrafast dynamics of polaritons formed upon strong light–matter coupling has been extensively studied by pump–probe spectroscopy. Although it was predicted that the partial photonic character of polaritons should shorten their lifetime compared to purely molecular excited states, many studies do not observe this effect. So far, the unexpected longevity of the spectral signatures has been either explained by relaxation into a manifold of so-called dark states or by other uncontrolled effects that change the properties of cavity materials. In order to resolve these issues, we investigate here the dependence of the line shape of pump–probe spectra of polaritons on the ratio of photonic and molecular character. Furthermore, by phenomenologically including relaxation to dark states, we find that it is possible to spectrally resolve this relaxation process by observing a characteristic phase flip in the pump–probe signal. Our results show that the signatures of dark state relaxation and the influence of the cavity resonance energy and their contributions to the polariton dynamics can be disentangled from the spectral line shapes.
Advanced Langevin thermostats: Properties, extensions to rheology, and a lean momentum-conserving approach
The Langevin equation accounts for unresolved bath degrees of freedom driving the system toward the bath temperature. Because of this, numerical solutions of the Langevin equation have a long history. Here, we recapitulate, combine, and extend existing Langevin equation based thermostats, scrutinize their properties, and demonstrate their superiority over global kinetic-energy controls. Our work includes compact, asymptotic-analysis based derivations of stochastic thermostats, including the highly accurate Grønbech–Jensen scheme. Proposed extensions include a precise, colored, and lean momentum-conserving thermostat.
The effect of bond functions on intermolecular interactions for van der Waals dimers of neon, methane, and perfluoromethane
We present a comprehensive study of intermolecular interactions in van der Waals complexes including the dimers Ne2, (CH4)2, (CF4)2, CF4–CH4, CH4–Ne, and CF4–Ne, within the framework of second-order Møller–Plesset perturbation theory (MP2). This methodology was employed to compute and analyze the behavior of the reduced two-particle reduced density matrix (2RDM) and related two-particle density. It was shown that the region near the minimum of the correlation component of the 2RDM associated mainly with the Coulomb hole significantly affects the dispersion interaction energies of the systems concerned. As one of the consequences, the bond function approach to deal with the intermolecular correlation energies calculations was found to essentially and consistently enhance the convergence of the results with respect to the basis set size if the auxiliary functions were placed to cover the 2D minimum region. For asymmetric dimers, this general finding was further validated through a series of CCSD(T) calculations of the correlation energies.
Continuous-time multifarious systems. II. Non-reciprocal multifarious self-organization
In the context of self-assembly, where complex structures can be assembled from smaller units, it is desirable to devise strategies toward disassembly and reassembly processes that reuse the constituent parts. A non-reciprocal multifarious self-organization strategy has been recently introduced and shown to have the capacity to exhibit this complex property. In this work, we study the model using continuous-time Gillespie simulations and compare the results against discrete-time Monte Carlo simulations investigated previously. Furthermore, using the continuous-time simulations, we explore important features in our system, namely, the nucleation time and interface growth velocity, which comprise the timescale of shape-shifting. We develop analytical calculations for the associated timescales and compare the results to those measured in simulations, allowing us to pin down the key mechanisms behind the observed timescales at different parameter values.