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Thursday 20 August

Chemical Physics · Cross-listed from cond-mat.mes-hall

Quantum critical behavior in chains of hindered dipolar planar rotors

Wenxue Zhang, Muhammad Shaeer Moeed, Estevao De Oliveira et al. (+2 more)

We study the ground-state properties of linear chains of dipolar planar rotors hindered by a six-fold on-site potential, a model motivated by water molecules confined in the hexagonal cavities of beryl. Using density matrix renormalization group (DMRG) calculations, we locate the quantum phase transition between the disordered and ferroelectrically ordered phases using the von Neumann entanglement entropy and the Binder ratio of the polarization. A sweep of the six-fold pinning strength shows that increasing hindrance shifts the critical dipolar coupling gc to smaller values. These results suggest that crystal-field hindrance can promote, rather than suppress, dipolar ordering. This work has implications for ferroelectricity and quantum-device tuning in confined molecular rotors
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All authors Wenxue Zhang, Muhammad Shaeer Moeed, Estevao De Oliveira, Hui Li, Pierre-Nicholas Roy

Chemical Physics · Cross-listed from physics.optics

Computational Methods of Wave Propagation for Semiclassical Models of High Harmonic Generation in Bulk Solids

Ava N. Hejazi, Nicholas Karpowicz, Gregory D. Scholes et al. (+1 more)

We present a theoretical framework for self consistent treatment of nonlinear light-matter interactions in the ultra-fast strong-field regime based on numerical solution of Maxwell's equations and semiconductor Bloch equations. This framework is shown to describe high-order harmonic generation and propagation in bulk semiconductors, investigating differences in reflected and transmitted harmonic spectra due to propagation effects. We show that the propagation of the combined field of the driving laser pulse and generated harmonics in a bulk semiconductor significantly modifies the harmonic spectra, affecting interpretation of experimental results relating the transmitted harmonic spectra to the underlying electronic structure of the material. This model allows the self-consistent description of strong-field light-matter interactions in the non-perturbative regime, opening the way to explore the transition between fully classical and quantum regimes of interaction, tunneling and multiphoton regimes of material ionization, and perturbative and non-perturbative regimes of harmonic generation in bulk materials.
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All authors Ava N. Hejazi, Nicholas Karpowicz, Gregory D. Scholes, Julia M. Mikhailova

Chemical Physics

Vibrational Activation Triggers Ultrafast Excited State Intramolecular Proton Transfer in Single-Benzene Fluorophores

Brieuc Le Dé, Simon Huppert, Riccardo Spezia et al. (+1 more)

Single-benzene fluorophores (SBFs) are exceptionally light-weight quantum emitters which have recently been shown to display Excited State Intramolecular Proton Transfer (ESIPT) and highly tunable dual-fluorescence that could be exploited for multiple applications. Here, we employ excited-state molecular dynamics to investigate the ultrafast dynamics of ESIPT in two different SBFs, one of which with a new structure proposed in this work. We find that both single and double ultrafast proton transfers can be triggered by exciting specific molecular vibrations. Strikingly, the kinetic activation of these vibrations - selected by atomistic, symmetry-based analysis - can considerably enhance the yield of proton transfer(s), as well as direct the reaction towards either single or double-transfer products. In-depth analysis elucidates the origins of this vibronic control, providing atomistic guidelines through which both the rate and fate of ESIPT could be steered using ultrafast IR-Vis spectroscopies.
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All authors Brieuc Le Dé, Simon Huppert, Riccardo Spezia, Alex W. Chin

Chemical Physics

Observables and Anti-Hermitian Generators in Time-Dependent Unitary Coupled Cluster Theory

Martin A. Mosquera

This work presents a time-dependent (TD) unitary coupled-cluster (UCC) formulation for electronic quantum dynamics, including the propagation of excited states and their superpositions, in both single- and multi-reference regimes. Standard TD coupled-cluster techniques offer size-extensivity, but they rely on non-Hermitian bivariational action functionals that break time-reversibility, giving transition matrix elements and amplitude estimators that are asymmetric (though accurate and systematically improvable). Here we use the time-evolution operator as an exponential map driven by TD anti-Hermitian cluster operators and first-order generators. Applying the Dirac-Frenkel action principle, we extract equations of motion governed by Heisenberg-picture-like commutators. This approach connects to our previous non-Hermitian formulations, where observables are expressed in terms of regular and extended cluster operators. From that connection we obtain a generator cluster operator whose unperturbed TD limit leads to the UCC eigenvalue problem. Even though this problem can be exact, the time dependence of the generator holds only at short propagation times, so we use the generator to prepare the initial state and then propagate that state with the formal TD UCC equation of motion. The theory is tested on an extended hard-core Bose-Hubbard ring with connections to neutral atom chains, and we discuss the theory's present limitations and possible extensions.
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Chemical Physics

Incorporating multiscale mechanics in lithium-ion battery models

Andrea Giudici, Andres F. Galvis, Smita Sahu et al. (+4 more)

Lithiation-induced swelling in lithium-ion batteries generates stresses not only within active particles, but also across the surrounding non-active matrix, electrodes, and cell stack. These stresses can modify the chemical potential of lithium and therefore influence transport, reaction kinetics, and terminal voltage. We derive a reduced-order electro-chemo-mechanical model that captures this multiscale coupling while retaining a complexity comparable to standard Doyle–Fuller–Newman models. The electrode is modelled as a periodic array of spherical active particles embedded in a homogenised elastic non-active matrix. Exploiting the small stiffness of the non-active matrix relative to the active material, together with scale separation between particles, electrodes, and the full cell, we obtain an effective mechanical correction to the active-particle chemical potential and overpotential. This correction depends on particle swelling, electrode-scale strain, and macroscopic boundary conditions such as clamping or applied pressure. The resulting formulation can be incorporated directly into DFN, SPMe, and SPM frameworks, providing a computationally efficient route to include battery-scale mechanical effects in electrochemical simulations.
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All authors Andrea Giudici, Andres F. Galvis, Smita Sahu, Robert Timms, Colin Please, Jon Chapman, Jamie M. Foster

Chemical Physics · Cross-listed from quant-ph

SAKE: Spectral Autodiff Kernel Expansion for Geometric Liouvillian Transport. A Differential-Geometric Framework for Response Transport in Quantum Dynamical Systems

Eric R. Bittner, Carlos Silva-Acuna, Hao Li et al. (+1 more)

We introduce the Spectral Autodiff Kernel Expansion (SAKE), a differentiable computational framework for transporting nonlinear spectroscopic response between neighboring quantum dynamical models. Rather than recomputing multidimensional spectra independently for each Hamiltonian or Liouvillian, SAKE constructs local transport expansions about a reference model by combining forward-mode automatic differentiation with Duhamel transport theory. Automatic differentiation generates first-, second-, and third-order derivatives of the parameter-dependent Liouvillian, which are assembled into a pathway transport operator that maps the nonlinear response of a reference model onto neighboring systems. The framework is validated for a four-level excitonic dimer possessing an $su(2)\times su(2)$ symmetry by comparing second- and third-order transported pathway operators with exact projected transport matrices obtained from direct calculations. The third-order expansion accurately reproduces the projected transport operator and its associated pathway mixing. Beyond providing an efficient computational strategy, the transport operator reveals how coherent and dissipative perturbations redistribute amplitude among double-sided Feynman pathways, exposing mechanistic information that is not directly apparent from the nonlinear spectrum. SAKE thereby establishes a differentiable computational framework for nonlinear spectroscopy that supports efficient local parameter exploration, sensitivity analysis, and future inverse-design applications.
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All authors Eric R. Bittner, Carlos Silva-Acuna, Hao Li, Simon Paiva-Ortega

Chemical Physics

Nonzero-temperature vibronic spectra of polyatomic molecules from a zero-temperature classical trajectory

Davide Barbiero and Jiří J. L. Vaníček

By combining coherence thermofield dynamics with the single-Hessian approximation, we enable simulations of low- to medium-resolution vibronic spectra of weakly anharmonic systems at nonzero temperatures, at negligible additional cost relative to zero-temperature calculations. Single-Hessian coherence thermofield Gaussian wavepacket dynamics is exact in any harmonic potential, provided that the reference Hessian is that of the final surface. When applied to Morse systems of increasing anharmonicity and varying temperature, this method successfully captures excited-state anharmonicity and key temperature-dependent spectral features, including hot bands and broadening. By combining the method with on-the-fly ab initio dynamics, we demonstrate its utility by computing the absorption spectra of naphthalene, aminocoumarin C450, and phenyl radical, and the photoelectron spectrum of SeO$_{2}^{-}$ . Within the ab initio single-Hessian approximation, after the zero-temperature spectrum is obtained at the cost of classical molecular dynamics (on the order of hours), all nonzero-temperature spectra are computed in seconds.
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Chemical Physics

Resonance Raman spectroscopy from ab initio Hagedorn wavepacket dynamics

Davide Barbiero, Léa Zupan and Jiří J. L. Vaníček

We present a practical, ab initio time-dependent method using Hagedorn wavepackets to simulate resonance Raman (RR) spectra of polyatomic molecules. Hagedorn functions—Gaussians multiplied by specific polynomials—are used to represent RR initial and final states because these functions are exact solutions to the time-dependent Schrödinger equation for at-most-quadratic potentials and can be propagated at zero cost beyond that of propagating the guiding Gaussian. Using efficient recursive formulae to compute overlaps between Hagedorn wavepackets, we can evaluate RR excitation profiles for arbitrary spectral signals, such as fundamental, overtone, combination, and hot bands. We then construct the Stokes and anti-Stokes RR spectra from these profiles. We first validate the method in a two-dimensional displaced, distorted, and Duschinsky-rotated harmonic model against numerically exact split-operator calculations. Then, we apply the method to compute RR spectra of anthracene by performing dynamics on a 66-dimensional harmonic potential energy surface constructed from density functional theory calculations.
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Chemical Physics · Cross-listed from quant-ph

Resource-Efficient Bio-Molecular Docking on a NISQ-era Digital Quantum Computer

Tianqi Chen, Adrian M. Mak, Jianguo Li et al. (+3 more)

Molecular docking is a vital computational task in drug discovery, wherein the objective is to efficiently identify optimal binding poses between a ligand and a target receptor protein. Due to the combinatorial explosion of possible binding configurations, docking of large and flexible molecules remains a computationally intensive problem, especially at scale. Early studies have revealed that the molecular docking can be re-cast as a maximum vertex-weighted clique problem (MVWCP) problem on a compatibility graph to be solved classically. In this work, we proposed a hybrid quantum-classical approach for molecular docking leveraging the MVWCP formalism with a variational full-basis encoding (FBE) strategy, which enables efficient encoding of classical binary variables with Bloch sphere vectors. We further prove that a global minimizer of the FBE objective can always be chosen to be a pure product state, thereby providing a rigorous justification for its optimization using a unitary variational circuit. The molecular docking problem is first mapped to a cost Hamiltonian that is minimized within a variational framework, optimized via a randomized imaginary time evolution (ITE)-inspired warm start, and gradient-based techniques. Finally, we also executed the circuit on an IBM quantum computer, underlying the feasibility and of quantum-assisted optimization for structure-based drug design and point towards the broader utility of advanced encoding techniques in quantum optimization for computational biology.
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All authors Tianqi Chen, Adrian M. Mak, Jianguo Li, Jian Feng Kong, Chandra Verma, Sebastian Maurer-Stroh

Chemical Physics

Nuclear-Electronic Orbital Subsystem Density Functional Theory

Denis G. Artiukhin

We present a new computational approach based on Nuclear-Electronic Orbital and Subsystem Density Functional Theory. The resulting NEO-sDFT methodology enables quantum chemical calculations of large molecular systems composed of thousands of atoms while also describing selected protons quantum mechanically. A key feature of the associated program implementation is its flexibility in assigning quantum protons to subsystems, allowing different embedding schemes to be employed within a unified framework. The accuracy of NEO-sDFT is assessed by computing water dimer interaction energies, which exhibit errors of only a few meV compared to reference Nuclear-Electronic Orbital Density Functional Theory results. The favorable computational scaling of NEO-sDFT is further showcased through calculations on water clusters of increasing size, with up to 303 protons being treated quantum mechanically. Our results demonstrate that NEO-sDFT is an accurate and efficient approach for incorporating nuclear quantum effects into large-scale simulations, providing a foundation for future applications to proton transfer processes in biochemical systems.
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Chemical Physics

Rare Fluctuations from Normally Hyperbolic Invariant Manifolds

Stephen Wiggins

Freidlin–Wentzell theory converts weak-noise large deviations into a Hamiltonian variational problem. We study how a $k$-dimensional normally hyperbolic invariant manifold (NHIM) $N$ of the deterministic dynamics appears in this Hamiltonian system. Its zero-momentum copy $N_0=N\times\{0\}$ is invariant, but the Hamiltonian dynamics has $2k$ center directions near $N_0$: $k$ tangent to $N$ and $k$ conjugate covector directions. We construct the resulting local symplectic geometry and show that fluctuation extremals approaching $N_0$ backward in time at the strong normal rate form an $n$-dimensional exact Lagrangian invariant manifold carrying a single-valued action. A counterexample shows that a corresponding zero-energy section need not be normally hyperbolic within $H_{\mathrm{FW}}^{-1}(0)$. We then consider reaction dynamics. If a parameter moves a deterministic trajectory toward a codimension-one reactivity boundary, the minimum Freidlin–Wentzell action required to reach the boundary is quadratic in the distance from the threshold parameter. Its coefficient is determined by the relative motion of trajectory and boundary and by how effectively the available noise acts transversely. This deterministic boundary is distinct from a noise-dependent stochastic transition state or a committor surface. In a solvent–solute model, varying solvent mass moves the phase-space reactivity boundary while leaving the potential-energy surface fixed, changing the rare-event cost without changing the potential-energy barrier.
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Chemical Physics

A Comparative Study of Coherent and Action-Detected 2D Electronic Spectroscopies of a Multichromophore Photosynthetic System

Edoardo Amarotti, Ajeet Kumar, Luca Bolzonello et al. (+3 more)

Coherent two-dimensional electronic spectroscopy (C-2DES) is a powerful tool for resolving excitonic structure and dynamics in light-harvesting complexes with dense energy-level manifolds. In contrast, action-detected 2DES has seen limited use on such systems, and its capacity to reveal electronic structure and dynamics remains unclear. Here we compare C-2DES and fluorescence-detected 2DES (F-2DES) on the major plant light-harvesting complex (LHCII) at 78 K. C-2DES resolves excitonic features and their spectral evolution, mapping energy-transfer pathways. F-2DES shows strong cross-peaks, but these are largely time-invariant and dominated by incoherent mixing, obscuring the dynamics. C-2DES is therefore preferred for resolving ultrafast energy transfer in light-harvesting complexes and other large interacting networks. Combined, the two measurements directly quantify the suppression of population dynamics by incoherent mixing, confirming that nearly the entire LHCII trimer network contributes. We also identify pulse-shaper nonlinearities in F-2DES as spurious features, highlighting the need for rigorous artifact suppression.
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All authors Edoardo Amarotti, Ajeet Kumar, Luca Bolzonello, David Bina, Tõnu Pullerits, Donatas Zigmantas

Chemical Physics

Iterative Projection-Based Embedding Scheme Combined with Variational Quantum Eigensolver

Hongseok Choi, Kyungmin Kim and Young Min Rhee

Quantum embedding methods offer a promising route to extend quantum chemical calculations to large multiscale systems by treating a chemically important subsystem at a high level of theory while describing its surrounding environment at an affordable level. The methods are also quite relevant for quantum computing approaches based on hardware with limited resources. Here, we present an iterative projection-based embedding framework combined with VQE, in which the environment density is allowed to respond self-consistently to the refined electronic structure of the embedded subsystem described by VQE. Unlike conventional one-shot approaches where the environment remains frozen after the initial orbital optimization, the proposed iterative scheme alternates between the VQE-level treatment of the subsystem and a mean-field-level refinement of the environment until mutual self-consistency is achieved. The convergence behavior of the scheme is first examined using several small test systems. Its practical applicability is then demonstrated with a composite system with a CH2NH molecule sandwiched by two benzene rings, with the C=N dihedral angle rotating from 0 to 90 deg. The iterative procedure consistently converges within ~10 iteration steps across all tested geometries, yielding energies below the conventional one-shot embedding results. The converged results well reproduce the fully correlated reference energy employing the same active space, and the resulting potential energy surface with respect to the dihedral rotation is also in good agreement with the reference one. These results demonstrate that our iterative embedding framework is numerically robust and physically sound, yielding a self-consistent and reliable treatment of inter-subsystem correlation. We expect that its formulation will be particularly compatible with the emerging paradigm of quantum-classical hybrid computing.
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Wednesday 19 August

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

Dynamic Ensembles of Phosphine-Stabilized Gold Nanoclusters

Caitlin A. McCandler, Disha Sanwal and Jutta Rogal

Atomically precise phosphine-stabilized gold nanoclusters are commonly characterized by single-crystal X-ray diffraction, yet the extent to which these static structures represent finite-temperature behavior remains unclear. To explore the free-energy landscapes, equilibrium populations, and isomerization kinetics of these nanoclusters in the gas phase, we establish a general framework that combines molecular dynamics simulations based on a machine-learned interatomic potential with Markov state models (MSMs). Analysis of the MSMs indicates that experimentally reported crystal structures frequently correspond to minor metastable states or transient configurations rather than the dominant finite-temperature structures. Increasing ligand coverage systematically alters both the thermodynamics and kinetics of structural rearrangements, driving the transition from planar to three-dimensional gold cores while accelerating isomerization dynamics. Moreover, catalytically accessible geometries are often only minor members of the equilibrium ensemble, highlighting a trade-off between structural stability and surface accessibility. These results emphasize that ligand-protected nanoclusters need to be viewed as dynamic ensembles and their finite-temperature behavior cannot be fully captured by their corresponding crystallographic structures alone.
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Chemical Physics · Cross-listed from cond-mat.stat-mech

Quantum Rényi-Jarzynski Equality

Benjamin Bobell, Mert Okyay and Rahul Nandkishore

The Jarzynski equality provides a strict link between nonequilibrium work and equilibrium free energy changes. Its typical quantum formulations, however, rely on measurement protocols that destroy coherence. In this Letter, we use the resource-theoretic approach to derive a non-destructive quantum Jarzynski equality conditioned on the outcomes of an arbitrary bath observable. This yields the Rényi-Jarzynski equality, which quantifies a finite bath's drift from equilibrium under a non-adiabatic drive via the Rényi $k$-divergence. We further demonstrate that the Rényi-Jarzynski equality provides a tunable cost function for quantum optimal control problems where minimizing bath drift is desired, such as state preparation and gate design, enabling the minimization of cross-talk in finite quantum systems. Our toy model exhibits a transition between competing minima for some critical value of $k$, illustrating how the Rényi order tunes sensitivity to different regions of a bath distribution. Strikingly, when drive parameters vary across bath energy levels, minimizing bath drift requires generating system-bath entanglement.
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Chemical Physics · Cross-listed from math.AG

Equations of Tree Tensor Network Varieties

Serkan Hoşten, Niharika Chakrabarty Paul, Otto T. P. Schmidt et al. (+1 more)

We show that tree tensor network varieties, including tensor train varieties, are general Markov models associated to spaced trees. This allows us to prove that the prime ideals of these varieties are generated by minors of matrix flattenings. In the case of tensor train varieties, we discuss whether these minors form a Gröbner basis and provide a combinatorial method to compute the degree for order $3$ tensor trains.
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All authors Serkan Hoşten, Niharika Chakrabarty Paul, Otto T. P. Schmidt, Dmitry Skurt

Chemical Physics

Universal Machine-learning Molecular Dynamics at the Speed of Empirical Potentials

Tiancheng Li, Jianming Xue, Linfeng Zhang et al. (+2 more)

No interatomic potential has offered universality across chemistry, near-first-principles accuracy and the speed of empirical potentials at once. Here we introduce DPA4C, an equivariant potential whose architecture and compressed CUDA operators are co-designed under deployment constraints to pursue accuracy and efficiency together. Five variants spanning a 49-fold parameter range form the high-throughput end of the measured accuracy–throughput frontier. The largest variant approaches the accuracy of the MACE-Omat models at about two orders of magnitude higher measured throughput. The most compact reduces the energy, force and stress errors of the fastest existing universal MLIP by 61.4%, 48.1% and 34.3% at 1.92 times its saturated throughput. All five variants complete multimillion-atom simulations on a single GPU and run molecular dynamics for 2.048 billion atoms on 1,024 16-GB NVIDIA V100 GPUs at 83.3–91.2% weak-scaling efficiency. Compared with the MEAM empirical potential, DPA4C-Nano reaches 1.8 and 2.5 times the saturated throughput in single-GPU scans on the same V100 hardware for diamond carbon and FCC copper, respectively. DPA4C therefore brings quantum-trained universal accuracy into a regime of speed and system size previously associated with empirical potentials.
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All authors Tiancheng Li, Jianming Xue, Linfeng Zhang, Duo Zhang, Han Wang

Chemical Physics

Molecular Implementation of the Machine-Learned Skala Exchange-Correlation Functional in CP2K through GauXC

Franz Pöschel, Johann Pototschnig, Frederick Stein et al. (+6 more)

Machine-learned exchange–correlation (XC) functionals offer a route to improve Kohn–Sham density-functional theory without incurring the cost of explicitly correlated electronic-structure methods. Their use in production simulation codes, however, requires a well-defined mapping between the learned model and the host-code density representation. We formulate and implement a Skala-1.1 interface in CP2K through the external GauXC library. CP2K supplies the geometry, Gaussian basis, spin-resolved atomic-orbital density matrix, and communicator, while GauXC evaluates the XC energy, atomic-orbital potential matrix, and available nuclear derivatives. The interface accepts both all-electron and valence-only density matrices. The latter may arise from separable dual-space pseudopotentials or molecular effective-core potentials. Implementation errors are isolated from functional differences by comparing the Perdew–Burke–Ernzerhof (PBE) functional evaluated through GauXC with native CP2K PBE. The resulting interface gives consistent energies, forces validated against finite-difference total-energy checks, and force-based molecular-virial diagnostics for representative molecular cases. The dietGMTKN55 benchmark suite is evaluated with an all-electron Gaussian augmented plane-wave treatment for elements up to bromine and def2 effective-core potentials for the heavier elements. The resulting aggregate mean absolute deviation of 1.255 kcal/mol is within 0.012 kcal/mol of the corresponding Skala reference value of 1.243 kcal/mol. This work establishes a validated molecular implementation of Skala in CP2K through GauXC.
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All authors Franz Pöschel, Johann Pototschnig, Frederick Stein, Andreas Knüpfer, Thijs Vogels, Stefano Battaglia, Sebastian Ehlert, Jürg Hutter, Thomas D. Kühne

Chemical Physics · Cross-listed from physics.optics

Influence of metal nanoparticles on whispering gallery modes of a microcavity

Tulika Agrawal, Venkata Dantham, Shubhayan Bhattacharya et al. (+3 more)

Photonic microcavities offer high energy density and low mode volume and attract special attention due to wide range of applications. Subsequent developments in the area of plasmonic nanocavities have also opened up applications despite their high absorptive properties. In the last two decades, photonic-plasmonic hybrid microcavities have been investigated extensively. In this article, we have conducted a review of the literature on photonic and plasmonic systems individually as well as in hybrid systems. Along with the underlying physics, applications such as cavity quantum electrodynamics, lasing, sensing, nonlinear optics and Raman spectroscopy have been reviewed. The outputs of the systems for each applications have been discussed and compared for photonic and hybrid systems. This review will provide a thorough understanding of the effects of optical cavities and plasmonics and their applications.
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All authors Tulika Agrawal, Venkata Dantham, Shubhayan Bhattacharya, Aneesh Veluthandath, Stephen Arnold, Prem Bisht

Chemical Physics

Molecular Insights into Gas Nanofilms Confined Between Bulk Liquid Phases

Yafan Yang, Zufeng Zuo, Xingyu Zhao et al. (+2 more)

Nanometer-thick fluid films play a critical role in confined multiphase processes, yet the thermodynamics and stability of free gas nanofilms remain poorly understood compared with their liquid counterparts. Here, molecular dynamics (MD) simulations are employed to systematically investigate gas nanofilms confined between bulk liquid phases using Lennard-Jones argon as a model system. The results show that the surface tension decreases exponentially with decreasing film thickness, accompanied by an increasing magnitude of the negative disjoining pressure. Upon thinning, the planar gas film undergoes a distinct morphological transition from a stable planar state to a transient or persistent spherical bubble through the formation and growth of a liquid bridge. The film surface area strongly affects its thermodynamic properties, with larger areas producing stronger thickness dependence and larger deviations from classical density functional theory (cDFT) predictions. The closer agreement between MD and cDFT at smaller surface areas suggests that the discrepancy primarily arises from thermal capillary-wave fluctuations, which are included in MD but omitted in mean-field cDFT. Moreover, at small film thicknesses, the magnitude of the disjoining pressure increases with decreasing temperature, consistent with the enhanced sensitivity of the confined gas phase to thickness variations and contrasting with the trend generally reported for liquid nanofilms. These findings provide molecular insights into the thermodynamics and stability of gas nanofilms, with implications for confined multiphase transport and droplet coalescence.
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All authors Yafan Yang, Zufeng Zuo, Xingyu Zhao, Shuyu Sun, Denvid Lau

Chemical Physics

UBio-MolFM: Enabling Biomolecular Dynamics at DFT Accuracy and $10^5$ Atoms with One Untuned Potential

Lin Huang, Frank Peng, JiaJun Cheng et al. (+8 more)

Ion conduction, membrane permeation and metal recognition hinge on electronic structure, yet first-principles simulation reaches only hundreds of atoms. UBio-MolFM lifts that ceiling: a foundation model trained on 160 million quantum-chemical labels, its receptive field spanning non-covalent distances at near-linear cost. The barrier is cost, not principle. One untuned potential keeps force error near 20 meV/Å past a thousand atoms, reproduces water's X-ray structure and ion hydration, and holds an RNA Mg$^{2+}$ site without ion-specific parameters. Cyclosporine A pays 3.5 kcal/mol in water for its permeable conformer, gated by one kinetically asymmetric hydrogen bond that a fixed-charge model flattens. In a 108,964-atom KcsA channel on one GPU, the relaxed four-ion column is anhydrous in all five replicas, in direct contact in four—the knock-on geometry ten fixed-charge simulations never form. It remains orders of magnitude costlier. Where electronic structure decides the answer, first-principles simulation is in reach.
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All authors Lin Huang, Frank Peng, JiaJun Cheng, Zion Wang, Hao Yin, Hao Li, Ji Zhang, Jack Jia, Junping Zhao, Arthur Jiang, Jia Zhang

Chemical Physics

Science Done on a Machine by a Machine: AI Agents in Computational Chemistry

Pavlo O. Dral, Hassan Nawaz and Arif Ullah

We are witnessing an explosion of agentic systems for computational chemistry: from four in 2024 to seventeen in 2025 and over sixty now, surveyed here. What is delegated to these systems is shifting from single calculations to whole in silico experiments and even manuscript writing. The ultimate destination is a fully autonomous AI scientist, where the entirety of computational chemistry is performed on a machine by a machine, without human supervision. Our survey shows that these systems are turning into vetted chemistry skills on general-purpose coding agents, and that they must be evaluated not only on their final answers but also on whether their calculations actually support these answers. The role of the human computational chemist is shifting from performing calculations to directing and supervising them, and the field should invest in the judgement that makes the supervision reliable: we propose a reporting standard, an evaluation reproducing published studies, a controlled comparison with general-purpose coding agents, and how to teach.
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Tuesday 18 August

Chemical Physics

Polyaniline as a conductive polymer and its role in improving the efficiency and conductivity of perovskite solar cells

Mehran Hosseinzadeh Dizaj

This article investigates the role of polyaniline as a conductive polymer in the active layer of perovskite solar cells. Samples were created by incorporating polyaniline into the transport layers to assess its impact on enhancing efficiency and conductivity. The application of this polymer across various layers of the cell structure led to improved stability and performance. Given its high doping capability, polyaniline was examined in detail, particularly focusing on two types of oxidation doping and its integration into the hole transport layer. Graphene oxide and reduced graphene oxide were chosen as comparative models, and their performance was evaluated against the standard polyaniline configuration. Laboratory results revealed that power conversion efficiency increased by 17.5% with graphene oxide and by 36.8% with reduced graphene oxide. Furthermore, short-circuit current density improved by 9.8% and 23.1%, respectively. These findings are consistent with existing studies in the field and support the validity of the approach.
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Chemical Physics

Multi-Species Multi-Reaction Model Parametrization of a Commercial NCA Positive Electrode from Half-Cell Open-Circuit Potential Data

Michele Galasso, Petr Čech, Ivo Horstkötter et al. (+3 more)

Physics-based models of lithium-ion batteries require the open-circuit potential (OCP) of each electrode as a function of its lithiation. The multi-species multi-reaction (MSMR) model provides a compact, thermodynamically grounded description of this relationship, representing each insertion reaction by a standard potential, a site fraction and a disorder parameter. Here, we parametrize the MSMR model for nickel-cobalt-aluminum oxide (NCA), a cathode chemistry widespread in automotive cells, using the positive electrode of a commercial silicon-graphite/NCA cell. Cathode material was harvested from a pristine cell and from cells cycle-aged to the end of life under two state-of-charge windows, and its half-cell OCP was measured by slow galvanostatic cycling. Smooth differential-capacity curves were obtained by histogram counting, and the charge and discharge branches were fitted with a constrained, scale-invariant optimization that keeps every reaction anchored to a visible peak. We report the first MSMR parameter set for an NCA cathode and show, through a differential-capacity peak analysis across aging states, that its thermodynamic signature is essentially unchanged by aging. This finding supports the common modeling practice of holding the electrode's intrinsic parameters fixed and ascribing aging to electrode-level capacity and alignment changes.
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All authors Michele Galasso, Petr Čech, Ivo Horstkötter, Simon Schwunk, Zuzana Vlčková Živcová, Václav Knap

Chemical Physics · Cross-listed from physics.atom-ph

Directional Hydrogen Migration in Acetonitrile Dication in Asymmetric Ultrashort Intense Laser Fields

Sato Miyasaka, Yuki Ono, Hiroka Hasegawa et al. (+3 more)

We investigate intramolecular hydrogen migration in acetonitrile dication in phase-controlled $\omega$-$2\omega$ intense laser fields (800 and 400 nm, 3.3$\times$10$^{14}$ W/cm$^2$) using three-dimensional coincidence ion momentum imaging. The two-body Coulomb explosion pathway, CH$_3$CN$^{2+}$ $\rightarrow$ CH$_3^+$ + CN$^+$, exhibits a clear phase-dependent fragment asymmetry along the laser polarization direction, showing that the tunnel ionization preferentially prepares the acetonitrile dication with the methyl group pointing toward the smaller amplitude side of the laser electric fields. The Coulomb explosion pathway occurring after the migration of a single hydrogen atom, CH$_3$CN$^{2+}$ $\rightarrow$ CH$_2^+$ + HCN$^+$, shows a pronounced reduction in the fragment asymmetry. A clear deuteration effect observed for the asymmetry of the hydrogen-migration pathway suggests that the two-color asymmetric laser field has a significant impact on directionality of intramolecular hydrogen migration in acetonitrile dication.
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All authors Sato Miyasaka, Yuki Ono, Hiroka Hasegawa, Runa Kuroda, Akitaka Matsuda, Akiyoshi Hishikawa

Chemical Physics

Coupled-cluster molecular properties across the main group that extrapolate beyond training size

Wenhao He, Xu Chen, Noah Song et al. (+10 more)

Coupled-cluster theory defines the accuracy standard for molecular electronic-structure properties but scales too steeply for routine application, whereas density-functional theory is affordable yet systematically biased. We resolve this trade-off with a single equivariant network, HARP (Hamiltonian Read-out for Properties), that predicts an effective one-electron Hamiltonian from one inexpensive B3LYP/def2-SVP calculation and derives a broad suite of properties from it (energy, optical gap, dipole, quadrupole, polarizability, Mulliken atomic charges, and Mayer bond orders) at coupled-cluster accuracy across nine main-group elements, including the under-served phosphorus, sulfur, and chlorine chemistries. The model is trained on a new in-house dataset of multi-property labels computed at the CCSD(T) level for all nine elements. On a held-out test set, it reduces the error of every property by a factor of 3.8 to 270 relative to semi-local, hybrid, and double-hybrid DFT (referenced to composite CCSD(T)/cc-pVTZ), while adding only ~0.1 s wall time per molecule, delivering coupled-cluster-quality predictions at the cost of a single DFT calculation. Critically, deriving every property from a predicted Hamiltonian rather than pooling per-atom features builds the correct size-scaling into the model architecture: on pi-conjugated oligothiophenes it matches finite-field CCSD polarizability to ~1% and the EOM-CCSD optical gap to ~3% at the largest sizes where those references remain affordable (44 and 37 atoms, where a single CCSD field point already costs ~500x the model's entire inference) and extrapolates the corrected trends to 58-atom chains, a regime where pooling-based architectures fail by construction. Accurate extrapolation is therefore set by the model's inductive bias rather than by the training data.
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All authors Wenhao He, Xu Chen, Noah Song, Haowei Xu, Tim S. Hindges, Bohan Li, Zihan Lin, Yu Yao, Avetik R. Harutyunyan, Fang Liu, Yao Wang, Hao Tang, Ju Li

Chemical Physics

Benchmarking Least-Squares Tensor Hypercontraction Techniques for Molecular Systems

Niklas Paulicks and Johannes Tölle

Finding a low-rank approximation for the two-electron integral (ERI) tensor is a crucial step towards reducing the computational cost of many-body electronic structure methods. In recent years, a range of new tensor factorization techniques, like the so-called tensor-hypercontraction (THC) approach, have been developed to achieve this goal. Unfortunately, a systematic comparison of accuracy and efficiency of different THC construction algorithms is missing. In this work, we address this gap by benchmarking these techniques across a wide range of molecular systems. In addition to offering useful insights into the advantages and disadvantages of the different techniques, we provide reference implementations in the newly developed open-source library, PyTHC.
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Chemical Physics

Operando multidimensional spectroscopy reveals A-site-dependent carrier cooling in perovskite solar cells

Edoardo Amarotti, Luca Bolzonello, Qi Shi et al. (+6 more)

Understanding how photogenerated carriers dissipate excess energy in operating perovskite solar cells is essential for connecting ultrafast photophysics with photovoltaic function and provides design principles for engineering next-generation cell architectures. Here we use photocurrent-detected two-dimensional electronic spectroscopy (PC-2DES) to resolve energy-dependent carrier relaxation in fully encapsulated, functioning metal halide perovskite solar cells. By comparing devices with identical architecture but different absorber compositions - MAPbI3, mixed FAMA, and FAPbI3 - we directly follow the redistribution of photoexcited carriers from initially populated high-energy states toward lower-energy band-edge states. The multidimensional photocurrent response reveals a cascade-like intraband cooling process whose rate depends strongly on absorber composition, with the slowest relaxation in MA-based devices, intermediate behaviour in mixed-cation devices, and fastest relaxation in FA-based devices. A reduced kinetic model incorporating phonon-mediated intraband scattering, supplemented by a phenomenological many-body contribution, captures the main energy-dependent trends. These results establish action-detected multidimensional spectroscopy as a device-level probe of ultrafast energy dissipation and show that subtle changes in perovskite composition can substantially reshape the carrier relaxation pathways that precede charge extraction.
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All authors Edoardo Amarotti, Luca Bolzonello, Qi Shi, Sun-Ho Lee, Torbjörn Pascher, Donatas Zigmantas, Niek van Hulst, Nam-Gyu Park, Tönu Pullerits

Chemical Physics

Chiral rotational dynamics in the molecular frame: Breaking symmetry with angular momentum

Alexander Blech, Monika Leibscher and Christiane P. Koch

Achiral molecules can be prepared in superposition states that are chiral. Here, we propose angular momentum orientation in the molecular frame to achieve the required symmetry breaking, exerting rotational control without the need for laboratory frame orientation. We derive the conditions for chiral rotational dynamics from the requirement to simultaneously break the continuous spatial rotational symmetry and the molecular point group symmetry. This can be achieved by three microwave pulses as well as two non-resonant optical pulses in combination with a THz pulse or three THz pulses, all with mutually orthogonal polarization directions, and the ensuing dynamics can be probed by photoelectron circular dichroism. Our results open the way for distinguishing structural from dynamical enantioselectivity and investigating time-odd chiroptical phenomena in randomly oriented molecules.
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Chemical Physics

Temporally Distinguishing Photocatalytic Dynamics

Catherine J. Fabiano, Shan Deneen, Yigao Yuan et al. (+4 more)

Light can induce both photothermal and nonthermal catalytic activity in plasmonic nanoparticles, but the extent, timescale, and efficacy of these two mechanisms remain unresolved. Here we introduce pump-pump photocatalysis, an adaptation of ultrafast excitation correlation spectroscopy in which incident laser pulses are split into two spatially and energetically equivalent pulses separated by a variable time delay. For a given reaction and catalyst, time-sensitive nonlinear enhancements in photocatalytic activity may be distinguished from time-insensitive responses as a function of time delay, pulse power, excitation wavelength, applied temperature, reactant pressure, and pulse asymmetry. In this way, the timescales of photothermal and nonthermal activity of any photocatalyst may be monitored on sub picosecond to nanosecond timescales, and the conditions for optimal chemical reactivity may be discovered. Here we report ultrafast measurements of the ammonia decomposition reaction using a Cu-Ru antenna-reactor photocatalyst. Photothermal contributions exhibit little sensitivity to pulse delay, while nonthermal contributions are most apparent at low excitation intensity, moderate temperatures, and sub-nanosecond timescales. Here, nonlinear, nonthermal mechanisms enhance H$_2$ production by a factor up to eleven compared to when pulses overlap. This technique may be used to provide unprecedented in operando diagnostics and control of any photocatalyst for any chemical reaction. Most importantly, these measurements allow us to ascertain the optimal distribution of light to maximize photocatalytic activity.
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All authors Catherine J. Fabiano, Shan Deneen, Yigao Yuan, Luke Kay, Peter Nordlander, Naomi J. Halas, Henry O. Everitt