Peer Revenue Publish or profit

Papers

Fresh from arXiv, typeset properly. Highlighted words trade on the market.

Physics Physics Chemical Physics

physics.chem-ph Watch Chemical Physics

Tuesday 18 August

Chemical Physics

Implementation Possibility of Quantum Simulation for Quantum Molecular Dynamics

Xingyu Zhang, Weijia Guo, Jinke Yu et al. (+1 more)

In this work, we explore the implementation possibility of quantum simulation for quantum molecular dynamics, in particular for reaction dynamics, though several implementations have already reported through quantum-classical mixed simulations (Acc. Chem. Res. 54 (2021), 4229 and J. Phys. Chem. Lett. xx (2026), XXXX). To analyze this aspect, we examine (1) the conjugacy relation between quantum simulator and the target molecular system, (2) the wave function correspondence in quantum algorithm and classical algorithm for multi-dimensional dynamics, (3) problems arisen from real-valued classical algorithms, and finally (4) geometric phase arisen from the separation among the degrees of freedom (DOFs). As is well known, the aforementioned first and second points play fundamental roles in quantum simulation of quantum many-body systems, and the third and fourth points are theoretical issues that might introduce problems in classical and quantum computing. In this work, we mainly focus on the third and fourth points by analysis of the first two points by reviewing previously reported quantum-classical mixed implementations of quantum simulation. We also consider gauge freedom in high-dimensional quantum molecular dynamics that has been introduced recently, and then discuss possibility of advantages and disadvantages of quantum simulation for molecular reaction dynamics.
Read the full abstract

All authors Xingyu Zhang, Weijia Guo, Jinke Yu, Qingyong Meng

Monday 17 August

Chemical Physics · Cross-listed from quant-ph

Evidence for cavity-induced metallic phase from entropic electron correlation effects

Jacob Horak and Dominik Sidler

Experiments have revealed that collective strong coupling in optical cavities can drastically alter the conductivity and dielectric properties of molecular ensembles, or even trigger abrupt phase transitions (in Rayleigh scattering or dispersion force driven conformational equilibrium). Until now, the underlying physical mechanism has remained unknown. A recently proposed theory attributes these collective effects to cavity-induced electron correlations that share properties of the known spherical Sherrington-Kirkpatrick model of a spin glass. As a consequence, entropic effects can trigger a phase transition in the inter-molecular electron correlations that could potentially explain the above experiments. In the following work, we derive analytic expressions for the correlation (free-)energy-induced polarizability changes, which reveal that under certain conditions collective strong coupling can even render our molecular ensemble metallic by entropically ionizing collectively degenerate molecular orbitals. Our results are a first major step towards a holistic theory of cavity-mediated electron correlation effects.
Read the full abstract

Chemical Physics

Through the Looking-Glass: Efficient Parity-Complete Learning via Local $O(2)$ Frames

Zemin Xu and Wenbo Xie

Making all symmetry-allowed tensor representations computationally accessible remains a central challenge in equivariant atomistic learning. Clebsch–Gordan tensor products (CGTPs) are computationally demanding, whereas efficient $SO(2)$-based alternatives lack a unified treatment of natural- and unnatural-parity representations. We first introduce a generalized Wigner-$6j$ convolution that exactly recouples interactions involving additional node representations, replacing the first edge-level tensor-product intermediate with reusable node features. This reduces edge computation and storage but leaves the $\mathcal O(L^5)$ angular scaling of the sparse CGTPs unchanged. To address this remaining bottleneck, we develop a local $O(2)$ framework whose convolutions scale as $\mathcal O(L^3)$. The framework explicitly accounts for both rotations and reflections. Its linear maps, tensor products, and gated nonlinearities, combined with frame transformations, ensure global $O(3)$ equivariance for both spatial parities. Incorporating time-reversal labels extends this construction to $O(3)\times\mathbb Z_2^{\mathcal T}$. We apply the framework to magnetic TACE (mTACE), using distinct interactions for systems with and without spin–orbit coupling. On collinear CrN and noncollinear Fe benchmarks, mTACE achieves substantial reductions in atomic- and magnetic-force errors. We also provide EquivariantX, a library for global and local $O(2)$-equivariant computation.
Read the full abstract

Chemical Physics · Cross-listed from quant-ph

Scientific applications of quantum computing: challenges and opportunities

Bruno Camino, C. Richard A. Catlow, John Buckeridge et al. (+13 more)

The predictive simulation of molecules and materials has had a broad and significant impact. It nevertheless remains constrained by the cost of accurately treating electronic correlation, excited states, and complex energy landscapes. Quantum computing offers a fundamentally different computational paradigm in which quantum states are encoded and manipulated directly rather than approximated on classical hardware. Here we discuss where this approach may provide a genuine scientific advantage in chemistry, materials science, and biochemistry. Promising directions include the high-accuracy treatment of correlated active spaces, improved excited-state simulations, and accelerated exploration of combinatorial structure spaces. The central challenge is therefore not qubit scaling alone, but demonstrably chemically meaningful gains in predictive reliability. We argue that near-term value is most likely to come from disciplined workflow integration rather than wholesale replacement of classical methods. Noisy physical devices, error-mitigated utility experiments, early fault-tolerant devices, and fully fault-tolerant quantum computers offer different scientific prospects, and claims of usefulness must be tied to the specific regime being discussed. Quantum computing will become scientifically valuable when it demonstrably reduces uncertainty in computed energies, rates, spectra, or materials stability after the full costs of state preparation, measurement, error handling, and coupling to classical simulation are included.
Read the full abstract

All authors Bruno Camino, C. Richard A. Catlow, John Buckeridge, Alin M. Elena, Vladimir V. Gusev, Sarah Harris, Thomas W. Keal, Glenn Jones, Vivien Kendon, Syma Khalid, Phalgun Lolur, Jamal A. Nasir, Matthew J. Rosseinsky, Chris-Kriton Skylaris, Paul A. Warburton, Scott M. Woodley

Chemical Physics

Unravelling carbene moiety role in the N-heterocyclic carbene-phosphinidenes coordination chemistry: bonding and reactivity in gold chemistry

Guillaume Thiam, Leonardo Belpassi and Paola Belanzoni

The coordination properties of the emerging class of N-heterocyclic carbene-phosphinidene (NHCP) ligands have been reported to be strongly affected by the carbene (NHC) moiety, but a clear understanding remains strikingly limited. In this work the bonding features and reactivity of 13 NHCP gold hydride complexes, [NHCPAuH], bearing different classes of NHCs have been systematically explored and compared to carbene analogues, using an unbiased computational protocol. The analyses reveal that, although the $\pi$-acceptor ability trend of NHCPs qualitatively parallels that of NHCs, the $\sigma$-donor ability trend reverses, with more $\sigma$-donating NHC moieties generating less $\sigma$-donating NHCP ligands. Concurrently, the nature of the NHC moiety impacts the coordination geometry at the P center, with the CNHC-P-Au bond angle appearing as a structural descriptor to monitor and/or design NHCP ligands with desired $\sigma$-donor properties. The NHCPs stronger $\sigma$-donor and weaker $\pi$-acceptor abilities compared to NHCs and their unique structural flexibility and electronic adaptability have been showcased to be directly controlled by the carbene moiety via modulation of the HOMO lone pair energy and its atomic phosphorous 3p character. The reactivity of [NHCPAuH] complexes with CO2, taken as a probe for potential NHCP applications in small molecule activation processes, demonstrates qualitatively similar mechanisms, with remarkably different activation barriers, which directly correlate with the NHCPs $\sigma$-donor ability, thus reflecting the high tunability of their bonding properties. This work provides insights and perspectives on the design principle of NHCP ligands, with a spotlight on the pivotal role of NHC moiety in modulating their electronic and steric properties, offering opportunities for burgeoning applications across diverse fields.
Read the full abstract

Chemical Physics

ChemReporter: A Framework for Curating and Exporting Large-Scale Chemical Datasets for MLIP Training

Marie Bluntzer, Jules Tilly and Christoph Brunken

Training set quality and diversity are key determinants of the reliability of machine learning interatomic potentials (MLIPs), yet using massive datasets in full is often impractical and redundant, making intelligent data selection essential. A major bottleneck, however, is the lack of infrastructure for uniformly accessing, curating, and subsampling heterogeneous large-scale chemical datasets, which differ widely in structure, metadata, and file format. We address this gap with ChemReporter, a modular, method-agnostic framework that converts arbitrary molecular and materials datasets into a unified, queryable representation and exports the results directly into MLIP-ready training data. ChemReporter operates in three decoupled stages: processing, which parses raw datasets into a partitioned Apache Parquet repository enriched with structural, physical, and chemical metadata; querying, which filters and samples this repository via a CLI or Python API using arbitrary selection criteria, from simple physical constraints to custom, user-defined strategies; and exporting, which streams the selected subset into an HDF5 file ready for direct use in modern MLIP training frameworks. Throughout this process, every exported data point remains traceable to its original source entry, and dataset exports can be reliably reproduced given the same configuration and query database version. Because data is stored in a queryable, disk-backed format, ChemReporter can process datasets far larger than available memory, allowing it to scale to billion-structure datasets on standard compute infrastructure. ChemReporter is available on GitHub and PyPI under the Apache License 2.0.
Read the full abstract

Chemical Physics

Extracting a nitrile-centered, ether-assisted motif hierarchy for lithium-battery electrolyte design from billion-scale molecular space

Yifeng Xia, Guanghui Wang, Sining Wang et al. (+4 more)

Designing electrolyte molecules for lithium batteries requires balancing electronic stability with appropriate Li+ solvation, yet the structural basis remains unclear across chemically diverse molecules. High-throughput screening expands the searchable space, but ranked candidates alone do not reveal recurring motifs or their applicability limits. We searched nearly one billion GDB13 structures using electronic–solvation descriptors without explicit functional-group preferences or scaffold constraints. Across descriptor weights, high-ranking populations separated into a nitrile-dominant regime and a coexistence regime containing substantial fractions of both nitrile- and ether-containing molecules. These regimes together define a nitrile-centered, ether-assisted motif hierarchy: nitrile remains favored across broad weight ranges, whereas ether becomes prominent under stronger electrostatic and polarity constraints. Encoding this hierarchy in a generative model expands the candidate space beyond GDB13 and yields high-scoring fluorinated structures without an explicit fluorination reward. Explicit-solvent molecular dynamics simulations show weak, exchangeable coordination of representative candidates without displacing ethylene carbonate from the dominant first solvation shell around Li+; effects on ion association and transport depend on molecular structure and concentration. These results establish a quantitative, interpretable and physically bounded motif hierarchy that systematizes established nitrile and ether chemistry for lithium-battery electrolyte design.
Read the full abstract

All authors Yifeng Xia, Guanghui Wang, Sining Wang, Wenting Chen, Zheng Cheng, Jinzhe Zeng, Qiangqiang Gu

Chemical Physics · Cross-listed from quant-ph

Optimizing Subspace Expansion in Quantum Chemistry through Operator Selection and Reference State Choice

Konstantin Lamp, Alejandro D. Somoza, Elias Walter et al. (+4 more)

The Virtual Quantum Subspace Expansion (VQSE) extends the Variational Quantum Eigensolver (VQE) by leveraging additional measurements on the reference state to capture the influence of excluded virtual orbitals. This makes VQSE attractive for chemical applications where accurate energy differences along potential energy surfaces are crucial for modeling reaction rates and kinetics. In this work, we analyze VQSE performance on H$_2$ dissociation including references that use Hartree–Fock molecular orbitals with broken spin symmetry. We identify two mechanisms which affect accuracy: overlap of the reference state with the exact full configuration interaction (FCI) wavefunction and operator pool expressivity. We show these mechanisms are strongly co-dependent. When operators are restricted to act only from the active to the virtual space, results become highly sensitive to the reference, and enlarging the active space does not guarantee improved accuracy. In this case, prioritizing reference overlap over energy minimization is therefore essential. Adding single excitations and number operators within the active space recovers the accuracy of MR-CISD (multi-reference configuration interaction singles and doubles) regardless of the reference. In our noisy hardware experiments, we achieve chemical accuracy by adding additional operators and using strict regularization. These findings motivate careful co-design of reference fidelity, pool expressivity, and hardware constraints for practical VQSE deployment.
Read the full abstract

All authors Konstantin Lamp, Alejandro D. Somoza, Elias Walter, Marina Walt, Michael Marthaler, Maria Fernanda Juarez, Birger Horstmann

Chemical Physics

Nonadiabatic Dynamics near Multiple Light-Induced Conical Intersections under Bichromatic Driving: Quantum Wave-Packet Dynamics versus Floquet Surface Hopping

Jiayue Han, Feng An and Wenjie Dou

Light-induced conical intersections (LICIs) create externally tunable pathways for nonadiabatic transitions, enabling active control of molecular photophysical and photochemical processes. However, both the dynamics near multiple LICIs under bichromatic driving and the applicability of our recently developed two-mode Floquet fewest switches surface hopping (two-mode F-FSSH) method to this regime remain insufficiently understood. Here, we construct a minimal three-channel Floquet Hamiltonian supporting two LICIs for Na2 interacting with a bichromatic field. We characterize its static Floquet properties and investigate the associated nonadiabatic dynamics using numerically exact quantum wave-packet dynamics and two-mode F-FSSH. We find that the second photon energy controls the relative positions of the LICIs, whereas the second-field intensity primarily redistributes and broadens the derivative-coupling landscape around the second LICI. Consequently, electronic population transfer and molecular alignment exhibit distinct and often nonmonotonic responses to these two control parameters. Two-mode F-FSSH reliably captures the principal features of the early-time dynamics and provides a semiquantitative description of the post-transient time-averaged observables. These findings advance our understanding of LICI-mediated dynamics at both the physical and methodological levels.
Read the full abstract

Chemical Physics

Highly Efficient 3-in-1 FPGA-Based Unit Combining an ADC, DAC, and Multichannel Pulse Generator for Pulsed EPR Spectroscopy

N. P. Isaev, A. R. Melnikov, A. V. Vedkal et al. (+4 more)

A hardware and software system for pulsed electron paramagnetic resonance (EPR) spectroscopy is presented, built around a single PCI Express (PCIe) card that combines a 16-bit digital-to-analog converter (DAC) with a 10 GS/s effective sample rate, a 2.5 GS/s 14-bit analog-to-digital converter (ADC), and an 11-channel pulse generator on board. Custom firmware reloads the pulse-generator and DAC buffers and streams the digitized data in parallel with a running experiment, so that no time is lost on data input or output. The unit is integrated into the open-source Atomize software and controlled at the level of pulse sequences through a high-level Python application programming interface (API). Benchmarking with a four-pulse double electron-electron resonance (DEER) sequence shows that the card reaches close to 100% time efficiency for accumulation times of a few milliseconds per pulse sequence, even for demanding arbitrary waveform generator (AWG) protocols. Although demonstrated for a single sequence, the efficiency proved insensitive to the number of pulses, the number of measurement points, or the phase-cycling depth, so that comparable performance is expected for any protocol whose shot repetition time exceeds the ~2 ms reprogramming time of the card. The on-the-fly reprogramming, which makes every successive sequence fully independent, also enables nonuniform sampling and acquisition. The system design, its firmware, the Python API, and its performance in pulsed EPR applications are described.
Read the full abstract

All authors N. P. Isaev, A. R. Melnikov, A. V. Vedkal, A. S. Ishchenko, A. M. Sokolov, E. A. Voronkov, S. L. Veber

Sunday 16 August

Chemical Physics

Gas-generating reactive flows in bicontinuous catalyst support structures

J.M.P. Beunen and J. Harting

A major challenge in the field of heterogeneous catalysis is selecting an optimal catalyst support structure. Commercially available structures can be easily manufactured at scale, but their stochastic nature makes their chemical and transport properties suboptimal. This is particularly relevant for gas-generation reactions, where non-uniformity of a porous structure leads to bubble trapping. Such trapping impedes the flow of reactants to catalyst sites, leading to conversion inefficiencies. Previous experimental work demonstrated that spinodally-derived architectures, in particular bicontinuous interfacially jammed emulsion gels (bijels), can alleviate these issues and deliver superior performance. However, to the best of our knowledge, numerical studies to optimize the operating conditions for such a morphology have not been performed yet. In this work, we aim to close this gap using color-gradient lattice Boltzmann simulations of reactive flows with a novel central moments collision operator. We develop an analytical model to predict catalyst performance based on our simulation data. Our findings show that this type of morphology can achieve very high conversion efficiencies. Moreover, we demonstrate that its catalyst performance can be optimized using superhydrophilic surface coatings.
Read the full abstract

Chemical Physics · Cross-listed from cond-mat.supr-con

Superconducting Hydride Mg2RhH6 Experimentally Achieved at Lower Pressure

Linjing Wu, Zelong Wang, Guiqi Liu et al. (+18 more)

Although tremendous progress has been made in recent years in the field of polyhydride superconductors, the realization of high critical temperature superconductivity still relies on formidable high pressures. Searching for superconducting hydrides at lower pressures is of particular importance. Here we report the first experimental synthesis of the Mg2RhH6, which achieves superconductivity under a significantly reduced pressure of 30 GPa. The synthesis of Mg2RhH6 proceeds via a two step process (1) preparation of the Mg2RhH5 precursor containing hydrogen atoms stabilized by covalent bonds, followed by (2) hydrogen supplementation resulting in the filling of electrons into anti bonding orbitals above 30 GPa, which was accompanied by the structural transition from RhH5 square pyramid to RhH6 octahedron. Superconductivity is achieved at 30 GPa with a Tc of 24 K, which is further enhanced to 29 K at 53 GPa, evidenced by a sharp drop of resistivity to zero and characteristic suppression of Tc under applied magnetic fields. Our experiments prove the Mg2RhH6 superconductor to be thermodynamically stable above 30 GPa, making it the first case exhibiting a Tc of approximately 30 K at a readily accessible pressure. This study pioneers a highly promising pathway for the rational design and discovery of high temperature superconductors within phonon mediated BCS framework.
Read the full abstract

All authors Linjing Wu, Zelong Wang, Guiqi Liu, Jun Zhang, Yanfeng Ge, Yuanhao Su, Runteng Chen, Hongyu Liu, Wenmin Li, Sijia Zhang, Jingcheng Zhu, Jianfa Zhao, Zheng Deng, Shaomin Feng, Jing Song, Qingqing Liu, Xiang Li, Haozhe Liu, Panpan Kong, Xiancheng Wang, Changqing Jin

Chemical Physics · Cross-listed from cond-mat.mtrl-sci

Intrinsic Wannier Functions for Hamiltonian downfolding

Shuoxue Li and Garnet Kin-Lic Chan

Downfolding ab initio material band structure into a low-energy subspace spanned by orbitals of specified atomic character, a procedure known as Wannier downfolding, is a common task in the simulation of complex materials. We introduce the Intrinsic Wannier Function (IWF) method to Wannierize bands with given atomic character. The method is non-iterative and requires only a single dimensionless parameter to disentangle bands. In benchmarks on silicon, graphene, and the three-band model of a mercury cuprate, we show that Intrinsic Wannier Functions provide high quality downfolded band structures compared to those from standard approaches such as Maximally Localized Wannier Functions and the Selected Columns of the Density Matrix method. Further, their straightforward implementation and robustness positions Intrinsic Wannier Functions as a general and useful tool for Wannier downfolding in materials electronic structure and in high-throughput applications.
Read the full abstract

Saturday 15 August

Chemical Physics · Cross-listed from cond-mat.mtrl-sci

Discovering Physically Interpretable Mathematical Expression for Predicting CO2 Adsorption in Metal-Organic Frameworks via Machine Learning-Symbolic Regression

Yimin Shao, Shengluo Ma, Shenghong Ju et al. (+2 more)

This work presents a machine learning-symbolic regression (ML-SR) strategy to develop a physically interpretable formula for predicting low pressure CO2 adsorption capacity in hypothetical metal-organic frameworks (hMOFs). Four ML models were trained on a small dataset of 1,000 samples, and five key descriptors-largest cavity diameter, pore limiting diameter, void fraction, gravimetric surface area, and number of hydrogen atoms-were identified through SHAP and feature importance analyses. Symbolic regression was then employed to derive a concise adsorption formula, Q=aA, where a represents an adsorption baseline (mmol/g) and A is a dimensionless adsorption number incorporating four structural descriptors. We interpret A as the ratio between an adsorption binding force and a diffusion driving force, revealing how pore topology and surface chemistry jointly influence adsorption. Validation against a comprehensive dataset of 137,652 hMOFs demonstrates that this formula achieves over 70% prediction accuracy for 62,448 structures, confirming strong applicability within defined structural and operational ranges. Unlike conventional black box ML models, the proposed physics-guided expression enables efficient prediction and provides clearer insight into adsorption mechanisms.
Read the full abstract

All authors Yimin Shao, Shengluo Ma, Shenghong Ju, Yijun Shi, Wei Li

Chemical Physics

Quantum Boltzmann Equation Self-Consistent-Field for the Entropic Regularization of Mean-Field Singularities

Romit Chakraborty

We present a Quantum Boltzmann Equation self-consistent-field (QBE-SCF) formulation for molecular electronic structure in which the one-electron reduced density matrix is propagated in an atomic orbital basis and relaxed by a Bhatnagar-Gross-Krook collision operator toward a Fermi-Dirac equilibrium defined by the instantaneous Fock matrix. At stationarity, the converged density and Fock matrices satisfy $[\mathbf{F},\mathbf{P}]=0$, the Hartree-Fock condition. While the zero-temperature equilibrium target reduces to the integer Aufbau projector, the damped collision operator ensures the steady-state density matrix is not necessarily idempotent. This kinetic relaxation affords a dual pathway to resolve mean-field singularities. For spatial degeneracies, such as H$_3$ symmetric dissociation, zero-temperature kinetic ergodicity fractionalizes the active space to recover the Generalized Valence Bond (GVB) limit. For the conical intersection in BeH$_2$ and the H$_4$ structural distortion ($D_{2h} \rightarrow D_{4h} \rightarrow D_{2h}$), finite-temperature entropic regularization recovers correlated adiabatic surfaces from a real-valued single-reference density. By maintaining stable numerical convergence across basis-set hierarchies and resolving static correlation without multi-reference wavefunctions, these results establish kinetic relaxation as a synthesis of single-reference electronic structure and quantum statistical mechanics.
Read the full abstract

Chemical Physics · Cross-listed from astro-ph.GA

Infrared Spectroscopy of Cyanonaphthalenes under Interstellar Relevant Conditions and Their Potential Connection with Astronomical Aromatic Infrared Bands

Jiaqi Xin, Jianzhi Xu, Piero Ferrari et al. (+1 more)

Context. Aromatic infrared bands (AIBs) are widely observed in diverse astrophysical environments and are generally attributed to vibrational emission from polycyclic aromatic hydrocarbons (PAHs). The recent interstellar detection of 1-cyanonaphthalene (1-CNN) and 2-cyanonaphthalene (2-CNN) has motivated detailed infrared spectroscopic studies of cyano-substituted PAHs. Aims. We aim to characterize the infrared spectra and vibrational modes of neutral 1-CNN and 2-CNN under cold and gas-phase conditions and to assess their possible spectroscopic relevance to the astronomical AIBs. Methods. The gas-phase infrared spectra of neutral 1-CNN and 2-CNN were measured in a cold molecular beam using ion-dip spectroscopy. The observed bands were assigned with the aid of harmonic and anharmonic calculations at the B3LYP/N07D level. Infrared emission spectra were subsequently simulated from the experimental spectra within a single-photon approximation framework. Results. We report the infrared spectra of neutral 1-CNN and 2-CNN measured under cold and gas-phase conditions relevant to the interstellar medium. Their vibrational features were assigned in detail, including fundamental vibrations as well as overtone and combination bands. The simulated emission spectra exhibit features in several wavelength regions associated with prominent AIBs, including the aromatic CH stretching region near 3.3 micron, the CC stretching region near 6.2 micron, the mixed CH in-plane bending and CC stretching region at 8.6-8.9 microns, and the CH out-of-plane bending region between 10 and 15 microns. Conclusions. The present spectra provide laboratory reference data for small cyano-substituted PAHs and offer useful clues for interpreting selected AIB regions. These results suggest that cyanonaphthalene molecules are promising contributors to the aromatic infrared bands.
Read the full abstract

All authors Jiaqi Xin, Jianzhi Xu, Piero Ferrari, Gao-Lei Hou

Friday 14 August

Chemical Physics · Cross-listed from cond-mat.mtrl-sci

Data-Efficient Construction of Material-Specific Machine-Learning Interatomic Potentials from Ab Initio Molecular Dynamics Trajectories

Jonas Hänseroth and Christian Dreßler

Pretrained machine-learning interatomic potentials, so-called universal or foundation models offer an appealing starting point for atomistic simulations, but their accuracy for material-specific observables often remains limited without additional reference data (fine-tuning). Here, we systematically quantify how much first-principles data are required to convert universal models into ab initio-accurate material-specific potentials, and ask whether fine-tuning is necessarily preferable to training from scratch. We compare five universal MLIP frameworks, MACE-MP-0, SevenNet-0, GRACE-1L-OAM, MatterSim-v1-5M and ORB-v2, across seven chemically diverse systems incorporating rare and reactive events. Fine-tuning on only 10 AIMD-derived configurations is insufficient for the investigated systems; 200 configurations succeed in favorable cases, but the outcome remains strongly system-dependent. By contrast, 2000 AIMD configurations constitute a robust default, yielding low force and energy errors and reproducing the target material-specific observables. Moderately dense sub-sampling of the AIMD trajectory reduces the required trajectory length tenfold with little loss in model quality. Training from scratch on the same datasets is competitive with, and often slightly more accurate than, naive fine-tuning for MACE and SevenNet, whereas GRACE requires more data. The energy profile for a sulfur-vacancy jump in MoS$_2$ reveals that low trajectory-level errors do not guarantee a correct reaction profile, highlighting the need for observable-level validation. Finally, we show that averaging independently trained models improves predictions in scarce-data regimes at no additional first-principles cost. Together, these results provide practical guidelines for converting limited AIMD reference data into reliable material-specific MLIPs for nanosecond-timescale simulations at near-DFT accuracy.
Read the full abstract

Chemical Physics · Cross-listed from cond-mat.mtrl-sci

When do machine-learned exchange-correlation improvements inherit into density-functional tight binding?

Can Polat, Mustafa Kurban, Erchin Serpedin et al. (+1 more)

Machine-learned exchange-correlation functionals correct band gaps at near-semilocal cost, while density-functional tight binding reaches the $10^3$-$10^6$-atom regime; combining them assumes that a better parent yields a better parameterization, but we show it does not. Current-generation functionals are orbital-dependent generalized Kohn-Sham operators, whereas the parameterization channel is built on a multiplicative potential, preventing exact representation. Using the transfer ratio, the surviving fraction of a parent-level change, we find anti-transfer: coherently negative ratios across four covalent semiconductors move the gap in the wrong direction, consistent with a molecular proxy and an r$^2$SCAN control. The minimal-basis overgap is dominated by the on-site convention rather than basis incompleteness; correcting the on-site block removes most of it, while one $d$-polarization shell closes a further $16$-$40%$, depending on the placement of the empty $d$ level, which no free-atom eigenvalue uniquely fixes. Occupied-manifold enhancements, ionic and closed-shell repulsive potentials, and rocksalt-oxide gaps inherit, whereas elemental and III-V covalent networks inherit neither gaps nor repulsive potentials and oxide networks inherit only the latter. We screen 23 elements and release the parameter sets, showing that the transfer ratio provides a cheap pre-test before any parameterization campaign.
Read the full abstract

All authors Can Polat, Mustafa Kurban, Erchin Serpedin, Hasan Kurban

Chemical Physics

Separation of Flexible Enantiomers Using Shear Flow

Minh Nhat Pham, Levi Cherek and J. Daniel Gezelter

Mechanical separation of enantiomers is an attractive alternative to synthetic methods for producing enantiopure samples. Shear flow that produces solution vorticity has been shown to be a viable means for separating chiral objects on the micro- to nano-scale due to the tensorial nature of the interactions between chiral objects and the surrounding fluid. A recently-developed theory of molecular pitch characterizes these interactions using the resistance tensor and predicts the shear-induced separation of drug-like molecules from their optimized molecular geometries. We present a molecular dynamics study on the effects of incorporating molecular flexibility into the molecular pitch framework. We also evaluate the potential for enantiomeric separation of two drug molecules: bicalutamide (Casodex) and montelukast sodium (Singulair). Simulations reveal the emergence of flexibility-induced pitch distributions that result from conformational changes occurring in a realistic solvent environment. However, these distributions are weakly influenced by the solvent identity and the shearing process, producing mean scalar pitch values that are close to those from optimized gas phase structures. Despite the opposing effect of translational diffusion at the molecular scale, racemic mixtures of flexible enantiomers show linear rates of separation at the 10 ns timescale, and we predict that cm-scale separation can be achieved within hours. Additionally, we provide estimates for parameters of a Taylor-Couette device for generating laminar shear flow, as well as considerations for future experiments.
Read the full abstract

Chemical Physics

Elucidating Trace Gas Interactions with Ice Surfaces using Molecular Dynamics

Benjamin M. Harless and J. Daniel Gezelter

Recent experimental work carried out by Yettapu, Manning, and Cyran on ice / vapor interfaces revealed changes in sum frequency generation (SFG) signals at ~ 3170 cm$^{-1}$ depending on whether acetone or methanol was adsorbed onto the ice at 223 K. They linked the transformation of that signal to the induced melting of the ice crystal. We present molecular dynamics modeling of their experiments using methanol and acetone layers adsorbed on the basal facet of a proton-ordered Ice-Ih crystal at temperatures of 223 K and 265 K. The width of the quasi-liquid layer (QLL), O-H bond frequencies, calculated SFG signals, and hydrogen bonding statistics all indicate changes due to the presence of the adsorbates. While we see no significant adsorbate-based differences in QLL formation, we find at 223 K that acetone preserves under-coordinated waters that are associated with a secondary water with a low frequency O-H bond, while methanol integrates more fully into the hydrogen bonding network, resulting in a narrower distribution of O-H bond frequencies. This change in hydrogen bonding produces a local modification of the electric field, which may contribute to the difference in the experimental SFG signals at low frequencies.
Read the full abstract

Chemical Physics

GPU implementation of mixed quantum-classical Liouville molecular dynamics without momentum jump

Koji Ando

We implemented on GPU a mixed quantum-classical Liouville molecular dynamics simulation based on a momentum-jump-free theory. The trajectory spawning that was previously implemented on CPU for sampling enhancement was eliminated to avoid the overhead of thread divergence and dynamic memory allocation on the GPU. This achieved a speedup of an order of magnitude compared to the CPU computation with spawning, as well as a linear scaling with respect to the number of sampling trajectories.
Read the full abstract

Chemical Physics · Cross-listed from cond-mat.mtrl-sci

Universal Thermodynamic Interatomic Potentials for Crystalline Materials

Juno Nam, Bowen Deng, Xiaochen Du et al. (+3 more)

Free energies govern solid-state phase stability, yet computational materials discovery still relies largely on ground-state energies because free energy calculations require ensemble averages. We introduce the thermodynamic interatomic potential (TIP), which extends an interatomic potential from its static energy to a thermodynamically consistent Gibbs free energy model, with thermodynamic responses following from temperature and pressure by automatic differentiation. We implement TIP[UMA] using the universal potential UMA, train it on free energies from quasi-harmonic to molecular dynamics fidelity, and calibrate it to higher-resolution calculations or experiment. From a single evaluation, it returns the equation of state of a crystal and locates phase transitions among competing branches, including dynamically stabilized phases. Fine-tuning extends the model to alloy solubility limits and miscibility gaps. TIP makes the free energy as accessible as the potential energy, opening finite-temperature phase stability to high-throughput discovery.
Read the full abstract

All authors Juno Nam, Bowen Deng, Xiaochen Du, Luis Barroso-Luque, Benjamin Kurt Miller, Rafael Gómez-Bombarelli

Chemical Physics

Multidimensional Design of Metal-Nitrogen-Carbon Electrocatalysts for Direct Propylene Epoxidation

Songbo Ye, Qingyuan Han, Jingwen Chi et al. (+6 more)

Propylene oxide is a major industrial chemical whose production currently relies on hazardous chlorine- or peroxide-based oxidants. Direct electrochemical epoxidation using water as the oxygen source offers a sustainable alternative, but controlling oxygen-atom transfer against the competing oxygen evolution reaction remains a fundamental challenge. Here, we show that propylene epoxidation selectivity cannot be described by oxygen binding energy alone, but is jointly governed by oxygen adsorption, the potential of zero charge, and applied potential. By combining theoretical calculations with pH-field-coupled microkinetic modeling across 41 metal-nitrogen-carbon single-atom catalysts, we first identified an optimal oxygen-binding window and Co as the most favorable metal center. We then found that peripheral substituents can tune the PZC while largely preserving the optimal oxygen adsorption energetics, thereby providing an independent design dimension to further optimize the already favorable Co active site. This sequential, multidimensional design strategy identified CoPc-NH2-CNT as the optimal catalyst, delivering a record PO Faradaic efficiency of 70-80 percent for direct propylene epoxidation in aqueous electrolyte under ambient conditions. These results establish interfacial electrostatics as an independently tunable design dimension for controlling selective oxygen-atom transfer in electrocatalysis.
Read the full abstract

All authors Songbo Ye, Qingyuan Han, Jingwen Chi, Yuan Huang, Heng Liu, Di Zhang, Hitoshi Shiku, Li Wei, Hao Li

Chemical Physics

Is the TDDFRT representation of a molecular electronic transition unique?

Jérémy Morere and Thibaud Etienne

In this article a piece of the reference time-dependent density-functional response theory (TDDFRT) representation of molecular electronic transitions is studied through the one-body reduced difference density matrix. A first derivation route for that object has been reported in the literature based on the substitution of TDDFRT-related objects into an exact functional expression. We show in the text that the functional providing the exact object is not unique, and we question whether substituting the same TDDFRT-related objects into the alternative functional expressions leads to acceptable candidates for the approximate TDDFRT one-body reduced difference density matrix, which would question the unequivocality of the TDDFRT representation of molecular electronic transitions. We first directly address the problem using a novel diagrammatic language, inspired by Dyck languages, and specifically designed for dealing with this kind of issue. In the last part of the article we question whether it is possible or not to recast the problem in a more general framework - the equations-of-motion framework. Through all the text, the case of time-dependent Hartree-Fock is compared with that of TDDFRT to highlight what makes them so different when those questions are at stake.
Read the full abstract

Chemical Physics

Poly(1,4-anthraquinone) as an Organic Cathode Material: Simulation of Observable Bonding Properties to Li, Na, Mg, and Ca

Laura Femmer, Lukas Köbbing, Juliane Heitkämper et al. (+9 more)

Poly(1,4-anthraquinone) (P14AQ) has emerged as a promising cathode material, offering high capacity and good cycling stability, yet the atomic-scale mechanisms governing metal-ion binding and electrochemical behavior remain poorly understood. To address this, we investigate the binding mechanisms of Li, Na, Mg, and Ca to P14AQ using quantum mechanical methods, particularly DFT and DFTB. A key challenge lies in the material's structural complexity: multiple conformers of P14AQ are energetically similar but kinetically isolated due to significant energy barriers. To account for this, we develop an automated method to generate all unique P14AQ conformers for a periodic polymer chain without rotational duplicates through an orientation labeling scheme. For each conformer, we systematically place a metal atom adjacent to every oxygen site, enabling a complete exploration of binding configurations. We observe two structural motifs: a single metal-oxygen bond and coordination to two opposite oxygen atoms. While Li and Na exhibit continuous energy distributions, Mg and Ca show an energy gap between the two motifs, with a strong preference for the two-oxygen binding configuration. Galvanostatic measurements support these findings by showing lower gravimetric capacities for Ca and Mg than for Li and Na. For Na, the different numbers of metal-oxygen bonds are reflected in the two voltage plateaus observed experimentally. Overall, the combined computational and experimental results explain the higher capacity of monovalent ions in P14AQ: divalent ions cannot bind efficiently to a single oxygen site due to unfavorable energetics, and the conformational distribution of the polymer chain prevents optimal coordination.
Read the full abstract

All authors Laura Femmer, Lukas Köbbing, Juliane Heitkämper, Sibylle Riedel, Devran Cay, Florin Adler, Birgit Esser, Alexander J. C. Kuehne, Zhirong Zhao-Karger, Piotr de Silva, Juan Maria García-Lastra, Birger Horstmann

Chemical Physics · Cross-listed from cond-mat.mtrl-sci

Electrostatic Phenomenology Benchmarks for Machine-Learned Interatomic Potentials in Electrochemistry: Beyond the Energy-Force Metric

Barbara Sumić, Ria Vasdev, Sudheesh Kumar Ethirajan et al. (+8 more)

Accurate treatment of long-range interactions in machine learning interatomic potentials (MLIPs) is essential for electrochemical simulations. However, aggregate energy and force errors alone are insufficient to establish an MLIP's physical accuracy since they do not detect qualitative inconsistencies in the model such as the prediction of image-charge attraction, dielectric screening, or charge transfer. We introduce a benchmark suite EPhEct (Electrostatic Phenomena for Electrochemistry) of focused test cases designed to evaluate MLIPs on electrochemically relevant physical phenomena. The tests probe for image-charge attraction at a metal electrode, the splitting between longitudinal and transverse optical phonons as a probe of ionic and electronic screening, the dipole moment of interfacial water, and Fermi-level pinning during ion discharge. These tests establish a qualitative diagnostic routine complementary to aggregate energy-force metrics.
Read the full abstract

All authors Barbara Sumić, Ria Vasdev, Sudheesh Kumar Ethirajan, Jing Yang, Clotilde S. Cucinotta, Richard G. Hennig, Karsten Reuter, Stefan Ringe, Mira Todorova, Christoph Freysoldt, Jörg Neugebauer

Chemical Physics

Reaction-Transformation-Aware Flow Matching for Generalizable Transition State Generation

Kaipeng Zeng, Wenxi Zhai, Shengrui Xu et al. (+5 more)

Transition-state (TS) structures define the energetic barriers and mechanistic pathways of elementary chemical reactions, yet their identification remains computationally demanding because conventional saddle-point searches require expensive quantum-mechanical calculations. Recent machine-learning approaches have accelerated TS generation by predicting structures from reaction endpoint information, but they primarily learn geometric correspondence between endpoints and TSs, leaving the structural transformations underlying elementary reactions implicitly represented. To address this limitation, we introduce TransTS, a reaction-transformation-aware framework for generalizable TS generation from atom-mapped reactant-product pairs. TransTS explicitly learns atom-level structural transformations between reaction endpoints and integrates them with a unified atom-aligned geometric representation of reactants, TSs and products, enabling reaction-aware equivariant generation of TS geometries. TransTS is designed to provide reliable TS initial guesses for subsequent quantum-chemical refinement, where generated structures are evaluated not only by geometric similarity but also by their ability to converge to validated saddle points and recover the intended reaction pathways. Across IID and zero-shot OOD benchmarks, TransTS demonstrates improved TS initialization quality, with particularly strong generalization to unseen reaction distributions. On the challenging GDB-10-rxn and GDB-17-rxn OOD benchmarks, TransTS generates TS candidates that more frequently converge to validated saddle points and recover the intended elementary reactions after refinement than existing approaches under the same training regime. Scaling reaction coverage and model capacity further improves both geometric fidelity and refinement outcomes.
Read the full abstract

All authors Kaipeng Zeng, Wenxi Zhai, Shengrui Xu, Jie Zhao, Bowen Li, Shiyue Wang, Junchi Yan, Tong Zhu

Chemical Physics

Linear-response time-dependent density-functional theory with local range separation: Core and valence resonances of the neon atom

Jari van Gog, Felipe Zapata and Julien Toulouse

We investigate range-separated hybrids (RSHs) and locally range-separated hybrids (LRSHs) for linear-response time-dependent density-functional theory (TDDFT) Sternheimer calculations of the photoionization spectrum of the Ne atom. This system constitutes a stringent test for approximate exchange-correlation treatments because it exhibits both valence and core resonances with very different energy scales. Building on previous work employing a simple one-parameter local range-separation function, we assess here a more flexible two-parameter range-separation function designed to improve the high-density limit. We compare photoionization spectra and resonance parameters obtained with RSHs and LRSHs. We find that the LRSH approach with the two-parameter range-separation function provides an overall satisfactory description of the photoionization spectrum, including energies for both valence and core resonances. The lifetimes of the 2s $\rightarrow$ np valence resonances are also reasonably reproduced since their decay does not involve double excitations. In contrast, the lifetimes of the 1s $\rightarrow$ np core resonances are overestimated by orders of magnitude because their Auger decay channels involve double excitations that are absent in adiabatic, single-determinant TDDFT. Obtaining more accurate resonance widths within linear-response range-separated TDDFT would require using multideterminant schemes and/or adding a frequency-dependent response kernel.
Read the full abstract

Chemical Physics

Different Environments in Quantum Statistical Mechanics: To $\beta$ or not to $(k_{\mathrm{B}} T)^{-1}$

Ellen T. Ekstrøm, Jacob Pedersen and Ida-Marie Høyvik

We piece together textbook material to re-derive the parameter $\beta$ entering reduced density operators from quantum statistical mechanics. By re-deriving $\beta$, we show that the content of $\beta$ depends on the particular application of statistical mechanics. We focus on two different applications, namely, electronic-structure theory (new) and thermodynamics (standard). Specifically, we show that $\beta$ becomes proportional to the inverse Fermi energy, when the electronic states of a system interact with the infinitely many valence electrons in a metal. On the other hand, when the environment is a heat bath, $\beta$ takes the well-known form of inverse temperature. To highlight the importance of using the correct form of $\beta$, we explore statistical descriptions of a potassium atom adsorbed on a gold surface, where the valence electrons of gold represent the environment of potassium. By treating $\beta$ as the inverse Fermi energy, we are able to qualitatively reproduce the fractional charging of potassium. In contrast, if we interpret $\beta$ as the inverse temperature, extremely high and unphysical temperatures are required to reproduce the same qualitative picture. Thereby, we illustrate the fallacy of not separating the mathematical framework of quantum statistical mechanics from its pervasive thermodynamic application.
Read the full abstract

Thursday 13 August

Chemical Physics

Comparative measurements of DC electrical breakdown distributions in liquid nitrogen, liquid helium, and liquid argon

N. S. Phan, S. M. Clayton, R. Gautam et al. (+4 more)

We present a comparative study of DC electrical breakdown in liquid nitrogen, liquid helium, and liquid argon using a common cryostat, electrode assembly, voltage-ramp protocol, and analysis procedure. This common experimental configuration minimizes systematic differences that often complicate comparisons among cryogenic liquids, including variations in electrode geometry, stressed area, surface finish, and gap spacing. For each liquid, breakdown was characterized as a statistical distribution rather than by a single characteristic voltage, allowing the stochastic nature of the process to be examined. Measurements were performed both near saturated vapor pressure and under modest pressurization to assess the influence of bubble formation and related thermodynamic effects. Liquid argon exhibited a non-stationary "turn-on" behavior, with breakdown voltage increasing over repeated discharges, consistent with evolution of the local impurity environment or electrode surface state. Near saturated vapor pressure, liquid helium showed a bimodal breakdown distribution, with a lower-field component consistent with bubble-mediated processes. Liquid nitrogen exhibited higher breakdown fields than liquid argon and fields comparable to those measured in pressurized liquid helium, within the observed run-to-run variation associated with surface state. Taken together, these results support a comparative framework in which breakdown strength reflects both thermodynamic stability against bubble formation and the transport properties of the dominant negative charge carrier.
Read the full abstract

All authors N. S. Phan, S. M. Clayton, R. Gautam, T. M. Ito, L. Kadlec, C. M. O'Shaughnessy, T. J. Schaub