Browse Articles

The electron affinity and ionization potential of the solvated uranyl from the quantum embedding approach

The quantum embedding approach offers an efficient way for large-scale electronic-structure calculations, enabling reductions in computational cost while retaining high-level accuracy. This aspect is particularly crucial for the modeling of actinide solution systems. Here, we present a subsystem approach for predicting valence electron binding energies, including the electron affinity (EA) and the ionization potential (IP) of the solvated uranyl. This approach combines the equation-of-motion coupled cluster method for electron attachment/detachment and the mean-filed treatment via absolutely localized projection-based embedding scheme, using representative structures extracted from ab initio molecular dynamics simulations, together with our newly developed norm-conserving actinide pseudopotentials. Our results show that the EA of solvated uranyl can be well reproduced by using the quantum embedding approach, whereas the IP requires an expanded active high-level region because of its global character. Including the full first solvation shell yields a marked improvement for the IP. This work demonstrates that the accuracy of the embedding partition is determined not only by the apparent structural locality of the system but also by how spatially localized the electronic-structure property of interest is. We anticipate that the quantum embedding approach will provide an efficient route to reducing the computational cost of high-level quantum chemical calculations for complex actinide solution systems.

Isomer effects in orbital-resolved photoionization cross sections of C2H4O2: Role of continuum dynamics and shape resonances

We present ab initio calculations of total and orbital-resolved photoionization cross sections for the C2H4O2 isomers glycolaldehyde, acetic acid, and methyl formate from threshold up to 40 eV. The calculations were performed using the ePolyScat framework at the static-exchange (SE) and SE-plus-polarization levels. The total photoionization cross sections, obtained as the sum over all twelve valence orbitals, exhibit a similar overall energy dependence for all isomers, with systematic differences near the ionization threshold and in the region of the cross section maximum. In contrast, the orbital-resolved analysis reveals a pronounced isomer dependence. To justify the single-particle picture underlying the scattering calculations, electron propagator theory was employed; the calculated pole strengths for the outer-valence orbitals remain high (∼0.9), validating the use of Hartree–Fock initial states as adequate representations of the Dyson orbitals. The highest occupied molecular orbitals, dominated by nonbonding oxygen lone pairs, give rise to the largest cross sections. Pronounced shape resonances are observed in the HOMO channels in the 15.5–19.3 eV range, with positions and intensities strongly dependent on molecular structure. Partial-wave analysis shows that these features are primarily governed by the l = 4 component, with additional contributions from neighboring channels. These results demonstrate that, despite identical stoichiometry, differences in molecular structure lead to distinct continuum electron dynamics. The computed cross sections provide quantitative input for astrochemical models and provide insights into isomer-dependent behavior in UV-irradiated environments.

Canonically consistent quantum master equation for proton-transfer reactions

The canonically consistent quantum master equation (CCQME) method to treat system–bath dynamics is used to describe intramolecular proton transfer in the thioacetylacetone molecule (TAA, C5H8OS), modeled as an N-level quantum system coupled to a solvent. The solvent is represented as a harmonic bath (a continuum of oscillators) characterized by Ohmic–Drude spectral density. We benchmark the secularized population dynamics and steady-state populations predicted by CCQME against numerically exact hierarchical equations of motion (HEOM) theory and compare it to the corresponding secularized Redfield results. Our results reveal that Redfield dynamics deviates increasingly from the HEOM reference as the system–bath coupling strength grows. In contrast, for not too strong couplings, the secularized CCQME population dynamics remains consistent with HEOM over an extended system–bath coupling range and approaches the second-order mean force Gibbs state. A complementary non-secular calculation shows that retaining population–coherence coupling reveals limitations of the second-order treatment for coherence-sensitive observables.

Tracking water vapor homogeneous nucleation and droplet growth with spectroscopy and holography in a free expansion cloud chamber

We use a newly commissioned rapid expansion aerosol chamber facility to study the homogeneous nucleation of water vapor to form liquid droplets. We perform high-speed measurements to track the partitioning of water into vapor and droplets throughout the expansion process, including tunable diode laser absorption spectroscopy (TDLAS) to access the vapor concentration and in-line holography to track the size and concentration of nucleating droplets. We retrieve the peak saturation ratio achieved in each expansion from the TDLAS measurements in combination with adjusted thermocouple temperature readout. We monitor the number of nucleated droplets and their subsequent growth as a function of saturation ratio and observe the onset of homogeneous nucleation of water vapor occurring at a threshold saturation ratio near S = 5, in agreement with prior literature and classical nucleation theory. The trends we observe in average diameter and droplet concentration suggest that warm air pockets near the chamber walls inhomogeneously mix with cold air at the center of the chamber following expansion. Active forced mixing with fans yields more spatially uniform temperature readings across the chamber but also significantly broadens the droplet size distribution. Our results demonstrate the capability of TDLAS and holography techniques to track both water vapor and liquid water in the high saturation ratio environments necessary for the homogeneous nucleation of droplets. Our findings also reveal that droplet nucleation and growth dynamics are highly sensitive to turbulence.

Publisher’s Note: “Efficient spectra from atomistic simulation: A generalized master equation study of the air–water interface” [J. Chem. Phys. 163, 244709 (2026)]

Toward more accurate natural orbital functional approximations: Including 4-index cumulant contributions

Accurate modeling of bond breaking remains a central challenge for reduced density matrix functional theory (RDMFT). Although some modern functionals can yield reasonably accurate dissociation energies, they often fail to reproduce key properties of the dissociated fragments, such as a vanishing fragment population covariance (also known as the delocalization index) and the correct total spin angular momentum of each fragment (local spin). In this study, we revisit the construction of natural orbital functionals by correcting the cumulant contribution produced by the PNOF5 functional. Our method enforces known contributions of the cumulant to local spin fragments and the delocalization index at the dissociation limit. We obtain the closest cumulant consistent with these physically motivated constraints and subsequently purify the corresponding one- and two-electron reduced density matrices by imposing the standard P, Q, and GN-representability conditions. The resulting functional yields improved behavior in strongly correlated regimes. Benchmarking on the dissociation of the singlet states of N2, NO+, O2, S2, and CO shows that, in the dissociation regime, the energies computed from the updated cumulant exactly reproduce the complete active space self-consistent field energies. We further analyze the limitations of the approach and identify scenarios in which the current approach performs poorly. This study provides a pathway for systematically improving natural orbital functionals to achieve reliable bond-breaking calculations within RDMFT.

Theoretical analysis of high-order harmonic generation from the modeled molecular nanoring by an intense mid-infrared laser

High-harmonic generation (HHG) from an idealized theoretical model of the molecular nanoring is numerically investigated by using an intense mid-infrared laser pulse. The resultant nonperturbative HHG exhibits some distinctly different radiation characteristics compared to the traditional gas HHG. Specifically, the harmonic cutoff for a molecular nanoring extends slightly beyond the cutoff law of the gas HHG due to its large spatial scale. The observed extension of the harmonic cutoff in the molecular nanoring can be well explained by a generalized semiclassical three-step model. In the simulation, we also find that the ellipticity dependence of the harmonic intensity for the molecular nanoring is distinguishably weaker than that for the atomic target. The harmonic ellipticities from the molecular nanoring can be continuously controlled by the elliptically polarized laser field within a certain ellipticity range, which offers a promising route to produce ellipticity-tunable harmonic emissions. Our results obtained from the numerical idealized model of the molecular nanoring suggest a potential pathway for achieving atomic-like HHG by a laser pulse only with the intensity on the order of 1012 W/cm2, just like the case of the solid HHG. Compared with the gas HHG triggered generally by the laser pulse with the intensity order of 1014 W/cm2, the novel scheme has the advantages of better accessibility and practicability.

Achieving selective photochemistry on a metal surface by tuning the aromatic core

On-surface photochemistry provides a non-thermal strategy that can circumvent the side reactions and structural defects associated with thermal activation, enabling enhanced control over surface reactions. Among these, Ullmann coupling serves as a representative on-surface reaction for fundamental studies of reaction mechanisms and controllability. However, how the aromatic core of molecular precursors governs photoinduced C–Br activation on metal surfaces remains insufficiently understood. In this work, we investigated photoinduced Ullmann coupling on Au(111) using three dibromo molecular precursors with distinct aromatic cores. The three precursors show markedly different photoreactivities under 405 and 532 nm irradiation. Time-dependent density functional theory calculations reveal a photoinduced surface-to-molecule charge-transfer process. Combined with calculations of potential energy surfaces for C–Br bond dissociations, these results provide a qualitative rationale for comparing the relative tendency of photo-triggered C–Br cleavage at the surface. The results establish a direct correlation between photo-selectivity and the molecular aromatic core, providing mechanistic insight into light-controlled on-surface synthesis and offering design principles for tailoring light-responsive precursors toward desired carbon nanostructures.

Study on the structural stability and electrochemical behavior of high voltage LiNi0.5Mn1.5O4 spinel cathode materials based on aluminum site regulation

At high operating voltages, high-voltage spinel LiNi0.5Mn1.5O4 (LNMO) undergoes serious lattice distortion and Jahn–Teller effect, accompanied by slow Li+ diffusion kinetics, which greatly hinders its practical deployment. Herein, Al-substituted LNMO (LiNi0.5Mn1.5−xAlxO4) was prepared by ion infiltration, and the influences of Al doping on structural and electrochemical performances were comprehensively explored. Combined physicochemical characterizations verify that Al3+ preferentially occupies the 16d crystallographic sites of the spinel lattice. This modification reduces cation mixing and induces a mild lattice contraction, with no secondary phases detected. Electrochemical measurements demonstrate that the optimized LNMO-A0.05 possesses superior rate performance and cyclability. After 100 cycles at 0.2C, it maintains capacity retentions of 95.1% (25 °C) and 89.9% (55 °C). In situ XRD analyses confirm that Al doping effectively suppresses lattice distortion and irreversible phase evolution, switching the electrochemical reaction from a two-phase mechanism to a solid-solution reaction. Electrochemical impedance spectroscopy (EIS) characterizations reveal that Al doping reduces charge transfer resistance and, accordingly, elevates the Li+ diffusion coefficient to 7.91 × 10−16 cm2/s. Further density functional theory calculations demonstrate that the robust Al–O covalent bonds function as structural anchors to reinforce the lattice. Meanwhile, electronic delocalization accelerates ion migration and improves reaction kinetics. The assembled LNMO-A0.05/LTO full cell delivers remarkable performance, demonstrating great potential for practical use.

Potential structure induced effects of the hairpin motif in RNA to form the phase separated droplet like associate in different solution condition

Reversible associations of RNAs among themselves, or with RNA binding proteins through the process of phase separation, are found to be important in many different cellular contexts, including cellular responses to stress, gene regulation, development, and disease. Short RNA repeat sequences, which are mostly linked with many repeat expansion neurodegenerative diseases, are found to undergo phase separation and yield protein-free biomolecular condensates in vitro and in cells. However, the physicochemical principles governing phase separation of RNAs considering both sequence and structural aspects, especially for short RNAs, remain elusive. It is intriguing, as well as challenging, to characterize the RNA phase behavior at a submolecular resolution. Based on atomistic enhanced sampling simulations, here we report potential dynamic structural effects in the mutual association properties of a tetra loop containing 14-mer hairpin RNA. We show that the folded and unfolded conformations of the hairpin fragment lead to different energetic barriers for the formation of an associated pair. Unfolded conformation leads to the formation of gel like energetically stable associated phases spontaneously; the folded hairpin motif is found to yield droplet like associated phases accompanying by cations in solution. Overall, our findings illustrate that dynamic association/dissociation is energetically more favorable for folded RNA hairpins, and the presence of additional salt in solution assists the formation of dense droplet like associated phases, while ionic concentration plays a critical role in the formation and stability of the droplet like associated phase. These observations open avenues for exploring structure-based phase separation mechanisms of RNAs in the context of RNA mediated functional biomolecular condensate formation within cells and designing RNA based novel biomaterials.

Inelastic scattering of H2CCO ketene induced by He atoms and non-LTE analysis

This work deals with the rotational inelastic scattering of ketene (H2CCO) by helium atoms. A new three-dimensional potential energy surface is computed by adopting the explicitly correlated coupled cluster approach with single, double, and perturbative triple excitation [CCSD(T)-F12a] connected to the augmented-correlation consistent-polarized valence triple zeta (aug-cc-pVTZ) Gaussian basis set. A global minimum with a well depth of V = −57.48 cm−1 for (R = 5.93 bohr, θ = 89°, ϕ = 90°) is identified. Quantum scattering calculations involving the 16 lowest states up to JKaKc=817 for ortho form of ketene (o-H2CCO) and the 10 lowest ones up to JKaKc=909 for para form (p-H2CCO) are performed via the close coupling (CC) method up to total energy E = 500 cm−1. Then, rate coefficients are derived for both forms over the temperature range of 5–90 K using the Maxwell–Boltzmann distribution. A predominance of the transitions with ΔJ = ΔKc = 1 for both o-H2CCO and p-H2CCO is obtained. Radiative transfer investigation of excitation and brightness temperatures, as well as optical depth, under non-local thermodynamic equilibrium (non-LTE) conditions for several observed lines is also performed by exploring the determined rate coefficients.

Mesoscale dynamics and the microscopic origin of the <i>Q</i> 0-mode in molecular liquids: A molecular dynamics study of tetrahydrofuran

We investigate the microscopic origin of collective dynamics in molecular liquids at intermediate (mesoscale) length scales using large-scale molecular dynamics simulations of tetrahydrofuran (THF). In agreement with previous neutron scattering results, in this regime, the dynamic structure factor S(Q, t) of THF exhibits—apart from collective excitations—a non-diffusive relaxation process (the Q0-mode) characterized by a relaxation time that is nearly independent of wavevector transfer Q. Our results confirm that this behavior arises from a cancellation of diffusive contributions between the self and distinct components of S(Q, t), extending previous findings for water to a non-hydrogen bonded system with moderate dipolar interaction. By systematically comparing coherent and incoherent scattering functions, we demonstrate that the Q0-mode originates from localized center-of-mass motions occurring within transient cages formed by neighboring molecules. These motions are directly linked to the caged regime of the mean squared displacement and define a characteristic time and length scale for the onset of Fickian diffusion. In contrast, the corresponding relaxation observed in the incoherent scattering function of hydrogen atoms FsH(Q,t) includes additional contributions from molecular rotations, leading to longer relaxation times for the fast localized process. A detailed analysis of rotational dynamics shows that translational and rotational motions are weakly coupled and can be approximately factorized, allowing a quantitative interpretation of the differences between coherent and incoherent responses. The resulting picture provides a unified microscopic framework for mesoscale dynamics in molecular liquids and rationalizes recent neutron scattering experiments.

Single-molecule surface-enhanced Raman scattering: From exceptional sensitivity to reliable interpretation

Single-molecule surface-enhanced Raman scattering (SM-SERS) should no longer be judged mainly by whether it can detect Raman signals from individual molecules but by what conclusions those signals can support under heterogeneous local conditions. In the single-molecule regime, the recorded spectrum is the product of a coupled molecule–interface–nanocavity–excitation–detection system, shaped by local geometry, molecule–metal coupling, cavity evolution, and readout conditions. The central challenge, therefore, shifts from achieving extreme enhancement to defining measurement conditions well enough for reliable interpretation. Here, we propose different evidential standards for four classes of SM-SERS claims—occupancy, assignment, local state, and mechanism—and argue that multimodal and correlative validation should increase with the strength of the claim. We assess how major platform classes reduce different sources of uncertainty and identify the field’s most tractable priorities: transparent reporting of observables, assumptions, and data-processing pipelines; quantitative statistics and reproducibility metrics for the events on which conclusions rest; and hypothesis-driven controls matched to the claim being made. SM-SERS will become a trustworthy nanospectroscopic tool only when each claim is supported by evidence strong enough to address the uncertainties of the coupled local system that produced the spectrum.

Analysis of a non-LTE hypersonic spectrum of ethylene between 5880 and 6200 cm−1

Hydrocarbons are partly responsible for the opacity of warm Jupiters’ atmospheres in the infrared. Laboratory high-resolution spectroscopic data, including hot band rovibrational transitions, are crucial to model and interpret telescope observations. In this work, a set of six hot bands and 11 cold bands of ethylene (12C2H4) is observed using cavity ringdown spectroscopy between 5880 and 6200 cm−1. The ethylene sample is preheated to 650 and 850 K before being expanded through a Laval nozzle to produce a high Mach number expansion. The rotational temperature drops to ∼12–13 K in the jet, while the vibrational population accumulates in the first excited vibrational state ν10, from which all the observed hot bands originate. The observed transitions are assigned using the lower state combination difference approach; a set of A, B, and C rotational constants, along with the energy of the upper state, is determined using PGOPHER software for the 17 observed vibrational bands. The TheoReTS (Theoretical Reims-Tomsk Spectral data) model, employed to identify the upper vibrational states, will benefit from these newly identified transitions.

The effect of van der Waals interaction on the microstructure of EPD deposits: A simulation study

Electrophoretic deposition is a method of choice for generating coatings thanks to its ease of implementation and its ability to produce coatings of relatively large thicknesses in a single-step process. While this process also benefits from a large number of tunable parameters to adapt the coating to each application (such as applied electric field, particle concentration, and viscosity of the suspension), such freedom can make selecting parameters an overwhelming task. A better fundamental understanding of the microscopic phenomena and mechanisms at play during deposition can provide clues for a more efficient design of optimized coatings. Particle-based models, which allow for the systematic simulation of deposit microstructures across various process parameters, are particularly interesting for gaining insights into such systems. Nevertheless, such studies are rare and usually do not include the possibility of self-cohesion between particles, which is crucial for the final structure of the deposit. Here, we use particle-based simulations to study how barrier-limited aggregation influences the deposits formed under different applied electric fields. We show that self-cohesion indeed leads to different microstructures, both in the close vicinity of the substrate and in the bulk of the deposit, and we relate this to the mechanical signature of the deposits. Our results reveal that at high electric fields, the influence of self-cohesion on the resulting microstructures essentially vanishes beyond a critical field strength. This marks the transition from a deposition regime affected by aggregation to a regime largely dominated by volume-exclusion effects.

Temperature-dependent growth and orientation selection of ice on Au(111)

Although the structures of solid water on surfaces have been extensively studied, the role of deposition temperature in determining growth morphology and in-plane orientation remains unclear. In this study, we examine ice growth on Au(111) as a function of deposition temperature using low-energy electron diffraction (LEED) and atomic force microscopy. The characteristic 3×3R30° periodicity of bilayer hexagonal ice (BHI) observed near 136 K disappears above ∼144 K. This indicates that BHI is a kinetically stabilized phase that is only accessible under low-temperature deposition conditions. At elevated deposition temperatures, as exemplified by deposition at 148 K, multilayer ice Ih forms three rotational domains, resulting in an eighteen-spot LEED pattern. In contrast, in our amorphous solid water annealing experiments, crystallization produced a six-spot pattern rather than the eighteen-spot pattern. This indicates that the resulting structure is determined by the deposition temperature rather than simply by post-growth thermal equilibration. However, a simple lattice-overlap model based solely on geometric commensurability under the assumption of an ice basal plane fails to reproduce the experimentally observed rotational domains. These findings suggest that local interfacial environments on Au(111), including step-edge regions, may influence the macroscopic in-plane orientation of ice.

Activity enhances transport while competing interactions preserve structure in colloidal microphase formers

Colloidal models with short-range attraction and long range repulsion (SALR) have been extensively studied using theoretical and simulations methods due to their rich and universal equilibrium phase behavior. Using Brownian dynamics simulations, we study the dynamical phase behavior of active suspensions in which colloidal particles interact with each other via a SALR potential. Upon increasing the self-propulsion force of the particles, we observed that the structural transitions the active suspension undergoes resemble those observed in its passive counterpart by increasing the temperature of the thermal bath. However, when looking at the transport properties of active and passive suspensions with similar structure, we observed a clear mismatch. We demonstrated that increasing the activity enhances the particles mobility within the SALR fluid while simultaneously preserving the structure. This leads to a structure–dynamics decoupling induced by the activity while highlighting the structural memory of SALR potentials under non-equilibrium conditions.

Active space selection with self-healing diffusion Monte Carlo algorithms for periodic solids

Multideterminant Diffusion Monte Carlo (DMC) displays improved accuracy over single determinant DMC. Self-Healing Diffusion Monte Carlo (SHDMC) is a DMC based method that iteratively improves a multideterminant trial wavefunction. Although configuration interaction or complete active space (CAS) methods are very accurate and computationally feasible for many systems, they are not optimal for application to solids. SHDMC is accurate and designed for application to solids, so developing SHDMC based active space selection algorithms is a worthy endeavor. Here, we present and compare active space selection algorithms that are designed for use in conjunction with SHDMC, without relying on external approaches. For benchmarking, we calculated the ground state energy of a small unit cell of graphene and compared the results with a complete basis set extrapolated selected CI and a reference SHDMC trajectory. We found that systematically expanding the active space using an “auto-branching” algorithm optimally balances accuracy with computational practicality. To the best of our knowledge, this is the first work that demonstrates completely self-contained DMC-based active space selection algorithms that do not depend on external methods for determinant selection.

Liquid crystal theory of biomembranes

Biomembranes, which are primarily composed of lipid bilayers, are not merely passive barriers, but dynamic, complex materials whose shapes are governed by the principles of soft-matter physics. This review examines the shape problem in biomembranes from the perspectives of materials science and liquid-crystal theory. We apply the Helfrich elastic model to the biomembrane shape in an electromagnetic field, and we extend the Helfrich free energy to multilayer systems, drawing parallels between the focal-conic structures of smectic liquid crystals and the geometries of fullerenes, carbon nanotubes, and the icosahedral virus. The review concludes by highlighting the unifying power of continuum elastic theories in describing a wide range of membrane morphologies across biological and synthetic systems.

Dynamical arrest in colloidal monolayers induced by energy landscape

Using video microscopy, we experimentally investigate how a periodic potential landscape influences the dynamics of colloidal monolayers. The potential is generated by a layer of densely packed particles immobilized on the substrate, creating a spatially periodic gravitational field. In the absence of this external landscape, the monolayer behaves as a supercooled liquid: particles are temporarily confined by cages formed by neighboring particles but can escape over long time scales, allowing diffusive motion and structural rearrangement. As the strength of the imposed potential increases, the system undergoes a dynamical arrest. Particles become increasingly trapped in local minima of the external potential, leading to a dramatic slowdown of particle dynamics and a suppression of structural rearrangements. This strong spatial localization also hinders the cooperative motion of particles. As a result, dynamical heterogeneity is significantly reduced during the dynamical arrest. Our results show the critical role of the energy landscape in tuning colloidal dynamics and offer insight into dynamical arrest processes in complex environments.