Browse Articles
Discover research articles across all indexed journals
Diverse carbon units in high-pressure C–K system predicted from first-principles and machine-learning methods
Metal–carbon compounds are significant for their diverse carbon units, which exhibit distinctive electronic and bonding properties, and broad application potential. In this article, we present a detailed C–K phase diagram, constructed using the crystal structure prediction method, MAGUS, based on machine-learning potentials fitted from first-principles calculations, revealing diverse carbon units, from allylenide ions to graphene-like two-dimensional layers. We found that the Pnma C12K16 phase contains allylenide ions, which contribute to its insulating behavior. Meanwhile, the ambient-pressure stable Cmcm C12K4 phase contains potassium-intercalated carbon layers with unique pentagonal–hexagonal–heptagonal (5–6–7) carbon rings, which we term “σ-graphene.” This σ-graphene monolayer can be synthesized either by exfoliating bulk C12K4 using an electrochemical method or by removing potassium atoms via evaporating. Furthermore, Boltzmann transport calculations show that pristine σ-graphene exhibits a high electrical conductivity (∼5.5 × 107 S/m at 300 K), comparable with silver and copper, making it a promising material for electrical transport applications. In addition, σ-graphene demonstrates excellent adsorption capabilities for O2 and NO2, with adsorption energies of −0.503 and −0.528 eV, respectively, suggesting potential applications in catalysis and environmental monitoring. Our work highlights the C–K system as a versatile platform for synthesizing and applying novel carbon-based materials.
Maximum entropy solution to the Stieltjes moment problem in chemical physics
In the inverse Stieltjes moment problem, one seeks to reconstruct a non-negative distribution from its spectral moments defined on an unbounded interval 〈0,∞. In chemical physics, this problem arises when computing continuous quantities such as photoionization cross sections or electronic decay widths using discretized approximations to the electronic continuum. While Stieltjes imaging (SI) is the established method in this context, it provides only sparse, discrete sampling of the distribution. Here, we develop a maximum entropy (ME) approach to the solution of the inverse Stieltjes moment problem in the context of Fano theory of resonances, where the sought-after quantity is the decay width function. We implement two ME variants—with polynomial and exponential asymptotic damping—and introduce an averaging procedure over spectral moment orders that addresses convergence issues and provides reliable error estimates. Benchmarking against ab initio Fano-ADC data for molecular Auger decay and interatomic Coulombic decay, we show that ME achieves comparable accuracy to SI while providing a continuous representation of the function. Our results establish ME as a valuable alternative to SI, particularly when analytical continuation or additional verification is required.
Role of optical phonon in fluoride-ion conductivity of LaF3
Fluoride-ion (F−) conductors have attracted much attention as solid electrolytes for all-solid-state fluoride-ion batteries with high energy densities surpassing those of conventional lithium-ion batteries. Ion conduction is mainly determined by the carrier amount (n) and diffusion coefficient (D), and progress is being made in understanding and controlling n. However, it is necessary to quantitatively evaluate not only D itself but also the factors that govern it. In this study, terahertz time-domain spectroscopy (THz-TDS), Fourier transform infrared spectroscopy, and first-principles calculations are used to address the effective jump attempt frequency that governs D. Phonons contributing to F− ion diffusion span a broad range of frequencies rather than a single vibrational frequency, indicating that more complex multi-phonon processes are at work. Empirical relations indicate that the mode frequency of 3 THz corresponds to an activation barrier of ∼0.5 eV. Phonon absorption around 5 THz for LaF3 involves the F vibration with the long La–F bond length. The THz-TDS conduction increases with the phonon absorption. The loose coupling between F− and counterions to soften the lowest optically active mode increases F− conductivity.
Velocity measurement in porous media using steady-state free precession—Analytical solution to the Bloch–Torrey equation with flow
In this study, fluid velocity is measured in a porous medium using a magnetic resonance steady state free precession (SSFP) technique. As shown theoretically and experimentally in this study, the SSFP measurement under steady flow conditions produces a periodic steady state magnetization with a strong flow sensitivity. The Bloch–Torrey equations were solved analytically using a Fourier series to predict the distortion of the steady state response due to flow. The analytical solution accurately describes the measured steady state longitudinal magnetization and transverse magnetization phase to permit the determination of the fluid velocity in a Bentheimer sandstone core plug non-invasively.
Conformational change and diffusion dynamics of passive and active filaments in network environments
Structure and dynamics of filamentous molecules in cross-linked network environments are crucial for diverse biological processes. We perform a systematic study for the conformational change and diffusion dynamics of both passive and active chains in the polymer networks based on Langevin dynamics simulations. Our results demonstrate a series of intriguing phenomena, via tuning network bending modulus, volume fraction, and chain activity. For a passive chain, strong confinement of network accounts for a remarkable conformational compaction. A robust subdiffusion scaled with mean square displacement ∼ τα (α < 1) is observed in accordance with a long-time memory effect. Under the concentrated network condition, the stiffness of a network plays a role in stretching the chain and impeding the diffusion dynamics. For an active chain, self-propulsion of the chain can overcome the confinement of network, realizing a swollen conformation and a transformation from subdiffusion to normal diffusion. In a dense network with rigidity, active chain suffers from a non-monotonic conformational change. Moderate activity induces an unconventional collapse effect. Our work highlights the new physics arising from the interplay between activity, conformational degrees of freedom of the probed chain, and the cross-linked network structure, which has no analogy in a nanoparticle probe system.
Notably different interfacial behaviors of two molecules with similar structures revealed by second harmonic generation (SHG) scattering and reflection
To probe the subtle structural evolution of molecules on interfaces is both important and technically challenging. Second-order nonlinear spectroscopic methods with unique interfacial selectivity, including sum frequency generation and second harmonic generation (SHG), have been generally applied to obtain such interfacial information. Recently, we investigated the structural evolution of an amphiphilic dye molecule (D289) on the surfaces of vesicles composed of phospholipids or surfactants with the combination of SHG scattering and two-photon fluorescence (TPF) methods. Here, we investigate the interfacial behavior of another amphiphilic molecule (SD289), which has a similar structure to D289 with minor differences. By combining SHG scattering and SHG reflection, a notably different structural evolution of SD289 on the interface composed of mixed surfactants, including SDS (sodium dodecyl sulfate) and CTAB (hexadecyl trimethyl ammonium bromide), was revealed. It was observed that SHG emission from interfacial SD289 was more than 2 orders of magnitude lower than that from D289, which was induced by the difference in the averaged tilting angles (∼88° vs ∼40°) of the two molecules. The structural evolution of SD289 on the vesicle surface under various temperatures was further investigated by TPF emission from SD289. The enhancement of TPF efficiency of SD289 was also interpreted by its structural evolution on the interface. The results further demonstrate the capability of the combined spectroscopic methods in analyzing the detailed structural evolution of molecules on interfaces, which may shed light on the investigations of molecular structures and kinetics on the membrane surface in general.
Local atomic structural descriptor and crystal field determined Ru1− <i>x</i> Ir <i>x</i> O2 as oxygen evolution catalyst unifying stability and activity
Ru/Ir oxides represent the promising catalysts of oxygen evolution reaction (OER) with better stability than Ru oxides and lower overpotentials than Ir oxides. To elucidate the activity and stability mechanisms of Ru1−xIrxO2 at an acceptable computation cost, the proposed local atomic structural descriptors are used to predicate OER intermediate adsorption ability and solvation effect accurately, and the cluster expansion (CE) method is applied to determine the ground state at given Ir concentration. Further analysis shows that Ru–O–Ir local configuration is the atomic fingerprint of Ru1−xIrxO2 structures, unifying both OER activity and stability. Crystal field analysis reveals that the Ru atom makes the dz2 band center of the Ir site atom upshift to achieve weak *OOH adsorption for high OER activity, while Ir atoms effectively lower the t2g orbital of the Ru atom to stabilize the structures. Our work not only addresses the activity–stability trade-off in Ru/Ir oxides but also advances the fundamental understanding of descriptor-based and CE models.
Carboxylic acid induced restructuring of the Fe3O4(001) surface
The redox properties of Fe3O4 surfaces are central to many catalytic processes and enable dynamic, reduction-induced morphological restructuring during reactions. Here, we investigate the structural changes of the Fe3O4(001) surface during the decomposition of formic and acetic acids using scanning tunneling microscopy, X-ray photoelectron spectroscopy, and density functional theory (DFT) calculations. Both acids readily deprotonate, forming ordered carboxylate overlayers on the surface. Product formation pathways involve the removal of lattice oxygen, resulting in extensive surface restructuring. For formic acid, only a modest level of surface oxygen removal (∼3%) is observed, resulting in elongated pits along the octahedral Fe rows and exhibiting an aspect ratio of ∼3. In contrast, acetic acid induces more extensive reduction, with the removal of ∼20% of surface oxygen, yielding significantly larger pits while maintaining a similar aspect ratio. Repeated exposure to acetic acid further enlarges the pits, indicating preferential etching at step edges. DFT calculations reveal a mechanistic sequence in which lattice oxygen removal destabilizes adjacent Fe atoms, promoting their migration into the bulk and subsequent pit propagation and step edge formation. Together, these findings provide atomistic insights into the coupling between carboxylic acid conversion and oxide surface restructuring, underscoring the strong interplay between redox chemistry and morphological changes on catalytically active Fe3O4 surfaces.
Internal protein motion in a rough model potential
Proteins are understood to exhibit complex internal motions on multiple time scales in their rugged free energy landscapes and often show subdiffusive behavior that significantly influences their biochemical functions. In this study, we employ the fractional Fokker–Planck equation and continuous-time random walk models to investigate the anomalous diffusion of particles within rough confining potentials, drawing inspiration from protein internal dynamics. Our analysis reveals that the dynamics exhibit three distinct regimes: initial free subdiffusion, an intermediate regime where roughness markedly impacts motion, and a long-term thermal plateau due to confinement effects. We derive approximate expressions for the mean displacement and the ensemble-averaged mean squared displacement in the low-roughness limit, revealing good agreement with simulation results. Furthermore, our examination of the ergodic properties of the dynamics indicates that systems with high roughness exhibit enhanced weak ergodicity breaking. As a consequence, the time-averaged mean squared displacement does not reach a plateau but shows a power-law increase in time and individual trajectories intrinsically exhibit an amplitude scatter. In addition, we demonstrate that the mean maximal excursion effectively quantifies the extent of confinement, offering a robust measure for characterizing subdiffusive dynamics in complex systems.
Titanium phosphate glasses: Beyond tetrahedral network structures
The structure of titanium phosphate glasses (TiO2)x(P2O5)1−x with 0.70 ≤ x ≤ 0.75 was investigated by combining neutron and high-energy x-ray diffraction with solid-state 31P nuclear magnetic resonance (NMR) and Raman spectroscopy. The results were interpreted with the aid of an analytical model that delivers the composition dependence of the structural motifs. The structure of these materials was also simulated using ab initio molecular dynamics. A detailed 31P magic-angle spinning (MAS) NMR lineshape analysis, aided by the results obtained from double-quantum coherence spectroscopy, indicates the presence of P–O–P-connected network forming units at a level decreasing from 23% to 11% with increasing x. The diffraction results show a Ti–O coordination number of 5.32(7) at x = 0.715 that increases to 5.49(7) at x = 0.750. The findings demonstrate the prevalence of five- and six-coordinated titanium atoms and the coexistence of both two-coordinated oxygen atoms, O(II), and three-coordinated oxygen atoms, O(III). The Ti-centered polyhedra contribute to a network in which the phosphate groups form P–O(II)–Ti and P–O(III)–2Ti connections, with signatures that are evident in the 31P MAS NMR spectra. The results suggest that structural variability is a key factor in promoting vitrification in this atypical glass-forming system. The findings provide a benchmark for investigating the structure of other glass-forming materials based on networks of higher-coordinated polyhedral units.
Jahn–Teller-driven electric field response in excited octupolar molecules
We present a comprehensive theoretical model to describe the response of an excited octupolar molecule to a static external electric field, explicitly accounting for the critical role of vibronic interactions (Jahn–Teller effect). The key finding is that, regardless of the strength of vibronic interaction, excited octupolar molecules function like qubits with an electric dipole moment. The model unifies the treatment of electronic states and nuclear dynamics and reveals that the field-induced dipole moment and its anisotropy are not intrinsic electronic properties but are profoundly modulated by the coupling to vibrational modes. The temperature dependence of ensemble-averaged dipole moments, bridging the gap between single-molecule properties and bulk experimental observables, is calculated and analyzed. These results provide fundamental insights into the interplay between symmetry, vibronic coupling, and external perturbations in complex molecular systems.
Unveiling the CO2 hydrate phase diagram from computer simulation: Locating the hydrate–liquid–vapor coexistence and its upper quadruple point
Carbon dioxide (CO2) hydrates hold promising applications in capturing and separating CO2 for climate change mitigation. Understanding their behavior at the molecular level is, therefore, essential, and computer simulations have become powerful tools for exploring their formation and stability, providing valuable insights into their underlying mechanisms. In this work, we perform molecular dynamics simulations to compute the three-phase coexistence line involving the stability region where CO2 is in the vapor phase: CO2 hydrate–liquid water–vapor. This computation was previously inaccessible using the traditional three-phase direct coexistence technique. To achieve this, we employ a novel solubility-based method, which allows us to accurately evaluate the coexistence line. Our results exhibit excellent agreement with experimental data and, for the first time, accurately reproduce the hydrate–liquid–vapor equilibrium line of the CO2–water phase diagram. Finally, we have determined the upper quadruple point (Q2), where the four phases, namely hydrate, liquid water, liquid CO2, and vapor, coexist. Our pioneering result for the Q2 value shows remarkable agreement with experimental observations, validating the accuracy of our findings and representing a significant milestone in the field of gas hydrate research.
Development and implementation of explainable AI-based machine learning models for predicting hospital stay and treatment costs in cardiovascular patients
Hip adduction and abduction isometric force production in young football players: reliability of different testing protocols
Maple-seed-inspired asymmetric microdisk resonators
Enhanced UV resistance of polypropylene via copper nanoparticle incorporation for outdoor applications
Enhancing strawberry salt stress tolerance: morphophysiological responses to different silicon rates and sources
Abstract Salinity stress is a critical environmental factor that significantly reduces strawberry productivity. The aims of the present study were to evaluate the efficacy of four foliar-applied silicon (Si) sources such as nano-silica, organic silica, potassium silicate, and stabilized silicic acid and rates including zero, 10, and 30 mg Si L − 1 on morphological properties of strawberries in two salinity levels (0 and 50 mM NaCl). A factorial experiment in a randomized complete block design with three replications was conducted. Key physiological parameters such as chlorophyll contents, free proline, and fruit yield were measured. Results showed that stabilized silicic acid and potassium silicate at 30 mg L − 1 significantly enhanced photosynthetic pigment concentrations, reduced oxidative stress, and improved yield under salt stress. Additionally, Vis-NIR data coupled with partial least squares regression (PLSR) moderately predicted leaf Si content under saline conditions (R 2 = 0.453 and MSE = 1.94). These findings highlight the potential of Si fertilization to mitigate salinity impacts in strawberry, while precision spectral tools such as Vis–NIR spectroscopy can support non-destructive monitoring of Si-induced physiological responses.