Hasil untuk "Physical and theoretical chemistry"

Robin Janssen, Lorenzo Branca, Tobias Buck

Nonequilibrium chemistry is central to many astrophysical environments but remains a major computational bottleneck in simulations because solving the associated stiff ODE systems is expensive. Neural surrogates promise large speedups, yet existing studies rarely provide systematic comparisons of architectures or rigorous optimization toward both accuracy and efficiency. We introduce CODES, a principled framework for optimizing and benchmarking astrochemical surrogate models. Using CODES, we compare four neural surrogate architectures across four KROME-generated datasets spanning primordial and molecular-cloud chemistry with up to 287 reactions across 37 species. Dual-objective optimization reveals pronounced accuracy-efficiency trade-offs across architectures. Fully connected models achieve the highest accuracy and most reliable uncertainty estimates, while latent-evolution models show improved robustness under iterative prediction. Our results highlight the importance of systematic optimization and architectural comparison. The datasets, metrics, and benchmarking procedure are publicly released within CODES to enable reproducible surrogate benchmarking.

Judith Wurmel, John M. Simmie

Tunnelling reactions of molecules embedded on cryogenic noble-gas matrices are being used in fundamental studies of how reactivity varies with the nature of the supposedly inert matrix as well as pointers to the chemistry occurring in the interstellar medium on ice-grains. To these ends we present chemical kinetic rate constants for the \textit{cis} to \textit{trans} isomerisation of seleno-, thio- and monomeric formic acids and that of their three dimeric species, based on multidimensional calculations in the gas-phase, from 10~K to 300~K as a guide to the matrix reactions.

Nanako ITO, Tomooki HOSAKA, Ryoichi TATARA et al.

Deep eutectic electrolytes (DEEs) are attracting increasing attention as liquid-state electrolytes for secondary batteries because they are potentially low cost, display low flammability, and are environmentally friendly. However, to date limited DEEs have been developed and explored for lithium-ion battery (LIB) applications, with most reports showing unsatisfactory capacity retention, a narrow potential window for battery operation, and an unstable solid electrolyte interphase (SEI) layer leading. Herein, we develop DEEs based on lithium bis(fluorosulfonyl)amide, LiFSA, and a series of urea derivatives as Li ion-conducting DEEs. Despite similar structures for the urea derivatives, i.e. methylated urea, we found that 1,3-dimethylurea (1,3-DMU) could form Li ion-concentrated DEEs across a wide range of LiFSA : 1,3-DMU ratio, while the LiFSA : urea DEE was liquid only in a limited range of molar ratios, i.e. LiFSA : urea close to 1 : 4 (mol/mol). By examining the electrolyte structure via Raman spectroscopy, we observed increased aggregation for DEE with higher LiFSA concentrations. We further confirmed non-flammability and electrochemical stability among the DEEs with potential windows ranging from ∼3.35 V for LiFSA : urea (1 : 4) to an impressive 6.42 V for LiFSA : 1,3-DMU (1 : 2) at a Pt foil electrode. During charge-discharge of Li4Ti5O12 (LTO) electrodes, we observed good capacities and retention for the LiFSA : urea (1 : 4) and LiFSA : 1,3-DMU (1 : 2) DEEs. High Coulombic efficiencies (CEs) were achieved in the LiFSA : 1,3-DMU (1 : 2) DEE with its high LiFSA content that led to more substantial FSA-derived components in the SEI structures after cycling. We further tested positive electrode materials, including LiFePO4 that showed excellent capacity retention and CEs near 100 % across 50 cycles. In all, we find that the dimethylurea-based DEEs show an opportunity for non-flammable and high-voltage Li batteries.

Fathi Elashhab, Lobna Sheha, Nada Elzawi et al.

Gellan gum (Gellan), a versatile polysaccharide applied in gel formation and prebiotic formulations, is often processed to tailor its molecular properties. Previous studies employed gamma irradiation and chemical hydrolysis, though without addressing systematic scaling behavior. This study investigates the structural and conformational modifications of Gellan in dilute aqueous salt solutions using a safer and eco-friendly approach: atmospheric low-dose electron beam (e-beam) degradation coupled with viscosity analysis. Native and E-beam-treated Gellan samples (0.05 g/cm³ in 0.1 M KCl) were examined by relative viscosity at varying temperatures, with intrinsic viscosity and molar mass determined via Solomon–Ciuta and Mark–Houwink relations. Molar mass degradation followed first-order kinetics, yielding rate constants and degradation lifetimes. Structural parameters, including radius of gyration and second virial coefficient, produced scaling coefficients of 0.62 and 0.15, consistent with perturbed coil conformations in a good solvent. The shape factor confirmed preservation of an ideal random coil structure despite irradiation. Conformational flexibility was further analyzed using theoretical models. Transition state theory (TST) revealed that e-beam radiation lowered molar mass and activation energy but raised activation entropy, implying reduced flexibility alongside enhanced solvent interactions. The freely rotating chain (FRC) model estimated end-to-end distance (<i>R</i>_θ) and characteristic ratio (C_∞), while the worm-like chain (WLC) model quantified persistence length (<i>l</i>_p). Results indicated decreased <i>R</i>_θ, increased <i>l</i>_p, and largely unchanged C_∞, suggesting diminished chain flexibility without significant deviation from ideal coil behavior. Overall, this work provides new insights into Gellan’s scaling laws and flexibility under aerobic low-dose E-beam irradiation, with relevance for bioactive polysaccharide applications.

O. Sohier, A. Y. Jaziri, L. Vettier et al.

Characterizing temperate exoplanet atmospheres remains challenging due to their small size and low temperatures. Recent JWST observations provide valuable data, but their interpretation has led to diverging conclusions. Complementary approaches combining laboratory experiments and photochemical modeling are essential for constraining atmospheric chemistry and interpreting observations. We aim to identify chemical pathways governing the formation and evolution of neutral species and to assess their sensitivity to key parameters such as C/O ratio and metallicity. Our approach combines experimental and numerical simulations on H2-rich gas mixtures representative of sub-Neptune atmospheres, spanning a wide range of CH4, CO, and CO2 mixing ratios. A cold plasma reactor simulates out-of-equilibrium upper-atmospheric chemistry. A 0D photochemical model reproduces reactor conditions, guiding interpretation of key pathways and abundance trends. We observe the formation of both reduced and oxidized organic compounds. In CH4-rich mixtures, hydrocarbons form efficiently through methane chemistry, correlating with CH4 concentration and agreeing with models. In more oxidizing environments, particularly CO2-rich mixtures, hydrocarbon formation is inhibited by complex reaction networks and oxidative losses. Oxygen incorporation enhances chemical diversity and promotes formation of oxidized organic compounds of prebiotic interest (H2CO, CH3OH, CH3CHO), especially in atmospheres containing both CH4 and CO2. Atmospheres containing CH4 and CO, which balance carbon and oxygen supply without excessive oxidative destruction, favor efficient production of hydrocarbons and oxidized compounds. Out-of-equilibrium chemistry plays a key role in the diversification and organic complexification of temperate exoplanet atmospheres.

Cesar Mello Fernando Medina da Cunha

Functional Spectral Imaging (FSI) models image formation as the recovery of tissue surrogates such as density and stiffness from spectral perturbations of a self-adjoint elliptic operator. Rather than relying on reflectivity or relaxation kinetics, FSI tracks shifts of a truncated set of eigenmodes under controlled excitation, providing a non-ionizing and operator-theoretic route to contrast. Tissue heterogeneity is modeled as a small perturbation of L = -div(D grad) + gamma, with first-order Hadamard formulas linking local contrasts to eigenvalue shifts. Frechet derivatives and their adjoints yield gradients for variational inversion, stabilized by Tikhonov or total-variation regularization and modal truncation. Finite-element simulations show submillimetric localization (about 0.1-0.3 mm) and milligram-scale detectability (thresholds near 1 mg) under ideal noise. Retaining 10-15 modes preserves about 85 percent of anomaly contrast while suppressing noise. A spectral-entropy index separates compact from diffuse inclusions and acts as a morphology surrogate. FSI thus provides a mathematically controlled, non-ionizing framework for localized functional imaging, motivating validation in physical phantoms and in vivo studies.

Nayrim B. Guerra, Jordana Bortoluz, Andressa R. Bystronski et al.

Diseases caused by infections are becoming harder to treat as the antibiotics used become less effective. A combination of strategies to develop active biomaterials that enhance antibacterial effects are desirable, especially ones that cause fewer side effects and promote healing properties. The combination of nanotechnology with substances that have intrinsic antibacterial activity can result in the advance of innovative biomedical materials. In this sense, the goal of this work is to provide a summary of natural rubber latex materials obtained from the <i>Hevea brasiliensis</i> tree loaded with metallic and metal oxide nanoparticles. These nanoparticles have unique size-dependent chemical and physical characteristic that make them appropriate for use in pharmaceutical and medical devices, while natural rubber latex is a natural and biocompatible polymer with an intrinsic antibacterial effect. Moreover, we outline here the origin, extraction methods, and composition of natural rubber latex and different techniques for the synthesis of nanoparticles, including physical, chemical, and biological approaches. Finally, we summarize, for the first time, the state of the art in obtaining natural rubber-based materials with metallic and metallic oxide nanoparticles for biomedical applications.

Elspeth K. H. Lee, Xianyu Tan, Shang-Min Tsai

With JWST slated to gain high fidelity time dependent data on brown dwarf atmospheres, it is highly anticipated to do the same for directly imaged, sub-Jupiter exoplanets. With this new capability, the need for a full 3D understanding to explain spectral features and their time dependence is becoming a vital aspect for consideration. To examine the atmospheric properties of directly imaged sub-Jupiter exoplanets, we use the three dimensional Exo-FMS general circulation model (GCM) to simulate a metal enhanced generic young sub-Jupiter object. We couple Exo-FMS to a kinetic chemistry scheme, a tracer based cloud formation scheme and a spectral radiative-transfer model to take into account the chemical and cloud feedback on the atmospheric thermochemical and dynamical properties. Our results show a highly complex feedback between clouds and chemistry onto the 3D temperature structure of the atmosphere, bringing about latitudinal differences and inducing time-dependent stormy features at photospheric pressures. This suggests a strong connection and feedback between the spatial cloud coverage and chemical composition of the atmosphere, with the temperature changes and dynamical motions induced by cloud opacity and triggered convection feedback driving chemical species behaviour. In addition, we also produce synthetic latitude dependent and time dependent spectra of our model to investigate atmospheric variability and periodicity in commonly used photometric bands. Overall, our efforts put the included physics in 3D simulations of exoplanets on par with contemporary 1D radiative-convective equilibrium modelling.

Huaisheng Hu

Many researchers are interested in using TiO2 semiconductor photocatalysts to combat pollution and solve energy shortages. This study proposes a composite of TiO2 and biochar because TiO2 can only use 43 percent of the visible light from sunlight. Meanwhile, nitrogen doping has been used to improve the N-doped TiO2/biochar composite. The N-doped TiO2/biochar can improve the photocatalyst's spectral responsiveness and narrow the forbidden band width. This increases the photocatalyst's ability to absorb visible light. This study compared three different modalities of cephalosporin antibiotic removal with N-doped TiO2/biochar: electrocatalysis, photocatalysis, and photo-electro-chemical catalysis. Photo-electro-chemical catalysis was found to be far superior to single electrocatalysis and photocatalysis.

Fumihiro SAGANE, Akiya MURAMATSU

Mg plating/stripping reaction in Mg[N(CF3SO2)2]2/glyme based solution is studied by electrochemical quartz crystal microbalance method. During the cyclic voltammetry, the apparent mass decrease is observed in spite of the negative scan. The irregular response also appears in the Mg plating reaction with low constant current density apply. In the cases, Mg plating takes place locally and the size of each plating is relatively large of about 50 µm. The cross-sectional image of the plated Mg is tree-like structure, i.e., the large Mg crystal connects to the substrate with small contact area. From the results, we conclude that the specific Mg morphology causes the restoring force to the quartz substrate, resulting in the apparent mass decrease.

A. Tuck

Theoretical chemists have been actively engaged for some time in processes such as ozone photodissociation, overtone photodissociation in nitric acid, pernitric acid, sulphuric acid, clusters and in small organic acids. The last of these have shown very different behaviours in the gas phase, liquid phase and importantly at the air–water interface in aqueous aerosols. The founder of molecular dynamics, B J Alder, pointed out long ago that hydrodynamic behaviour emerged when the symmetry of a random, thermalised population of hard spheres—billiard balls—was broken by a flux of energetic molecules. Despite this, efforts over two centuries to solve turbulence by finding top-down solutions to the Navier–Stokes equation have failed. It is time for theoretical chemistry to try a bottom-up solution. Gibbs free energy that drives the circulation arises from the entropy difference between the incoming low-entropy beam of visible and ultraviolet photons and the outgoing higher-entropy flux of infrared photons over the whole 4π solid angle. The role of the most energetic molecules with the highest velocities will affect the rovibrational line shapes of water, carbon dioxide and ozone in the far wings, where there is the largest effect on radiative transfer and hence on calculations of atmospheric temperature. The atmospheric state is determined by the interaction of radiation, chemistry and fluid dynamics on the microscopic scale, with propagation through the mesoscale to the macroscale. It will take theoretical chemistry to simulate that accurately. A challenging programme of research for theoretical chemistry is proposed, involving ab initio simulation by molecular dynamics of an air volume, starting in the upper stratosphere. The aim is to obtain scaling exponents for turbulence, providing a physical method for upscaling in numerical models. Turbulence affects chemistry, radiation and fluid dynamics at a fundamental, molecular level and is thus of basic concern to theoretical chemistry as it applies to the atmosphere, which consists of molecules in motion.

Kai Leng, Qingkai Tang, Ying Wei et al.

Recently, double perovskite (DP) oxides denoted A2B′B″O6 (A being divalent or trivalent metals, B′ and B″ being heterovalent transition metals) have been attracting much attention owing to their wide range of electrical and magnetic properties. Among them, rhenium (Re)-based DP oxides such as A2FeReO6 (A = Ba, Sr, Ca) are a particularly intriguing class due to their high magnetic Curie temperatures, metallic-like, half-metallic, or insulating behaviors, and large carrier spin polarizations. In addition, the Re-based DP compounds with heterovalent transition metals B′ and B″ occupying B sites have a potential to exhibit rich electronic structures and complex magnetic structures owing to the strong interplays between strongly localized 3d electrons and more delocalized 5d electrons with strong spin–orbit coupling. Thus, the involved physics in the Re-based DP compounds is much richer than expected. Therefore, there are many issues related to the couplings among the charge, spin, and orbitals, which need to be addressed in the Re-based DP compounds. In the past decade, much effort has been made to synthesize Re-based DP compounds and to investigate their crystal structures, structural chemistry, and metal–insulator transitions via orbital ordering, cationic ordering, and electrical, magnetic, and magneto-transport properties, leading to rich literature in the experimental and theoretical investigations. This Review focuses on recent advances in Re-based DP oxides, which include their synthesis methods, physical and structural characterizations, and advanced applications of Re-based DP oxides. Theoretical investigations of the electronic and structural aspects of Re-based DP oxides are also summarized. Finally, future perspectives of Re-based DP oxides are also addressed.

Changwon Sung, Byung-Hyun Shin, Wonsub Chung

The pitting corrosion resistance of super duplex stainless steel (SDSS) varies depending on heat-treatment conditions. Therefore, in this study, the volume fraction and morphology of austenite on SDSS were controlled in 6 samples, and the effect on the pitting corrosion after solution annealing was analyzed to of the critical pitting temperature (CPT). The pitting-resistance equivalent (PRE = wt % Cr + 3.3 wt % Mo + 16 wt % N) was became equal by solution annealing, but the CPT exhibited varying values. Despite heat treatment of the solution annealing, the CPT increased by 15.9 °C from 67.5 °C to 83.4 °C. The solution annealing removed the segregation of the chemical composition and assisted in improving the PRE; however, it not removed in a non-uniform morphology of austenite. Therefore, the corrosion resistance of SDSS can be optimized by appropriately controlling the morphology of austenite during the manufacturing process.

Waheeda Saib, Petros Wallden, Ismail Akhalwaya

Variational quantum algorithms are suitable for use on noisy quantum systems. One of the most important use-cases is the quantum simulation of materials, using the variational quantum eigensolver (VQE). To optimize VQE performance, a suitable parameterized quantum circuit (ansatz) must be selected. We investigate a class of ansatze that incorporates knowledge of the quantum hardware, namely the hardware efficient ansatze. The performance of hardware efficient ansatze is affected differently by noise, and our goal is to study the effect of noise on evaluating which ansatz gives more accurate results in practice. First, we study the effect of noise on the different hardware efficient ansatze by benchmarking and ranking the performance of each ansatz family (i) on a chemistry application using VQE and (ii) by the recently established metric of "expressibility". The results demonstrate the ranking of optimal circuits does not remain constant in the presence of noise. Second, we evaluate the suitability of the expressibility measure in this context by performing a correlation study between expressibility and the performance of the same circuits on a chemistry application using VQE. Our simulations reveal a weak correlation and therefore demonstrate that expressibility is not an adequate measure to quantify the effectiveness of parameterized quantum circuits for quantum chemistry. Third, we evaluate the effect of different quantum device noise models on the ordering of which ansatz family is best. Interestingly, we see that to decide which ansatz is optimal for use, one needs to consider the specific hardware used even within the same family of quantum hardware.

Yinhui Li, Longfei Peng, Weixin Li

Biochar adsorbents used to treat different heavy metals in water are efficient and low-cost. Appropriate raw materials, excellent selectivity and detailed adsorption mechanism are of important for research on biochar adsorbents. In this work, konjac starch was dispersed in polyvinylpyrrolidone (PVP) solution to prepare different sizes hydrophilic carbon spheres (HCSs) by hydrothermal synthesis method. Adsorption kinetics of the HCSs towards Pb 2+ is described perfectly by the pseudo-second-order equation. With the temperature increasing, adsorption thermodynamics are more consistent with the Freundlich model. The calculated ΔG, ΔH and ΔS shows the adsorption of the HCSs towards Pb 2+ is a spontaneous, endothermic and entropy increase process. In addition, HCSs have excellent selectivity for the adsorption of Pb 2+ and Cu 2+ . HCSs prepared from konjac starch make full use of natural biomass resources, they can be used as a potential adsorbent material in treatment on heavy metal ion from water field.

Guangwei Wang, Hongzhen Chen

A YSZ oxygen sensor responded correctly to changes in oxygen concentration in an autoclave chamber, although at elevated pressures, the electron transfer numbers agreed well with the theoretical value of 4. The electrochemical impedance spectra (EIS) of the sensor at an oxygen concentration of 500000 ppm, a temperature of 873 K and pressures of 1-80 atm were determined, and those results demonstrated that the overall electrode resistances were strongly dependent on the pressure of the system, which was probably due to the change of physical and chemical characteristics of the working medium. This result is consistent with the strong impact of pressure on the response rate of the oxygen sensor working in a water content atmosphere at elevated pressures.

Hui Fan, Yangpei Zhao, Jie Jiang et al.

A new type of layered manufacturing technology that combines the jet electrodeposition method and a rapid prototyping concept is presented. The manufacturing method adopts multilayer scanning electrodeposition using an electrolyte jet to fabricate a micro-metallic part with a nanocrystalline microstructure, which simplifies three-dimensional processing. The research results showed that key parameters, including the current density, applied voltage, nozzle diameter and jet speed, impacted the forming process and deposition quality. The effective current density was observed to reach 350 A/dm2, at which point nanocrystalline grains with sizes from 30-50 nm were obtained. It was found that the application of an optimized applied voltage, nozzle diameter, current density and jet velocity increased the forming speed and improved the mechanical performance of the finished parts. A group of nanocrystalline copper parts with a good shape and mechanical properties was produced using optimized parameters with the jet electrodeposition method.

Dominik Sidler, Christian Schäfer, Michael Ruggenthaler et al.

Polaritonic chemistry has become a rapidly developing field within the last few years. A multitude of experimental observations suggest that chemical properties can be fundamentally altered and novel physical states appear when matter is strongly coupled to resonant cavity modes, i.e. when hybrid light-matter states emerge. Up until now, theoretical approaches to explain and predict these observations were either limited to phenomenological quantum optical models, suited to describe collective polaritonic effects, or alternatively to ab initio approaches for small system sizes. The later methods were particularly controversial since collective effects could not be explicitly included due to the intrinsically low particle numbers, which are computationally accessible. Here, we demonstrate for a nitrogen dimer chain of variable size that any impurity present in a collectively coupled chemical ensemble (e.g. temperature fluctuations or reaction process) induces local modifications in the polaritonic system. From this we deduce that a novel dark state is formed, whose local chemical properties are modified considerably at the impurity due to the collectively coupled environment. Our simulations unify theoretical predictions from quantum optical models (e.g. formation of collective dark states and different polaritonic branches) with the single molecule quantum chemical perspective, which relies on the (quantized) redistribution of local charges. Moreover, our findings suggest that the recently developed QEDFT method is suitable to access these locally scaling polaritonic effects and it is a useful tool to better understand recent experimental results and to even design novel experimental approaches. All of which paves the way for many novel discoveries and applications in polaritonic chemistry.

A. Taninah, S. E. Agbemava, A. V. Afanasjev

The systematic investigation of the ground state and fission properties of even-even actinides and superheavy nuclei with $Z=90-120$ from the two-proton up to two-neutron drip lines with proper assessment of systematic theoretical uncertainties has been performed for the first time in the framework of covariant density functional theory (CDFT). These results provide a necessary theoretical input for the r-process modeling in heavy nuclei and, in particular, for the study of fission recycling. Four state-of-the-art globally tested covariant energy density functionals (CEDFs), namely, DD-PC1, DD-ME2, NL3* and PC-PK1, representing the major classes of the CDFT models are employed in the present study. Ground state deformations, binding energies, two neutron separation energies, $α$-decay $Q_α$ values and half-lives and the heights of fission barriers have been calculated for all these nuclei. Theoretical uncertainties in these physical observables and their evolution as a function of proton and neutron numbers have been quantified and their major sources have been identified. Spherical shell closures at $Z=120$, $N=184$ and $N=258$ and the structure of the single-particle (especially, high-$j$) states in their vicinities as well as nuclear matter properties of employed CEDFs are two major factors contributing into theoretical uncertainties. However, different physical observables are affected in a different way by these two factors. For example, theoretical uncertainties in calculated ground state deformations are affected mostly by former factor, while theoretical uncertainties in fission barriers depend on both of these factors.

Pablo de Vera, Alexey Verkhovtsev, Gennady Sushko et al.

Irradiation- and collision-induced fragmentation studies provide information about geometry, electronic properties and interactions between structural units of various molecular systems. Such knowledge brings insights into irradiation-driven chemistry of molecular systems which is exploited in different technological applications. An accurate atomistic-level simulation of irradiation-driven chemistry requires reliable models of molecular fragmentation which can be verified against mass spectrometry experiments. In this work fragmentation of a tungsten hexacarbonyl, W(CO)$_6$, molecule is studied by means of reactive molecular dynamics simulations. The quantitatively correct fragmentation picture including different fragmentation channels is reproduced. We show that distribution of the deposited energy over all degrees of freedom of the parent molecule leads to thermal evaporation of CO groups and the formation of W(CO)$_n^+$ ($n = 0-5$) fragments. Another type of fragments, WC(CO)$_n^+$ ($n = 0-4$), is produced due to cleavage of a C--O bond as a result of the localized energy deposition. Calculated fragment appearance energies are in good agreement with experimental data. These fragmentation mechanisms have a general physical nature and should take place in radiation-induced fragmentation of different molecular and biomolecular systems.