Hasil untuk "Physical and theoretical chemistry"

A. Zangwill

P. Meakin

A. Klamt

Jing Zhu, E. Ha, Guoliang Zhao et al.

Jonas Köhler, Leon Klein, F. Noé

Normalizing flows are exact-likelihood generative neural networks which approximately transform samples from a simple prior distribution to samples of the probability distribution of interest. Recent work showed that such generative models can be utilized in statistical mechanics to sample equilibrium states of many-body systems in physics and chemistry. To scale and generalize these results, it is essential that the natural symmetries in the probability density - in physics defined by the invariances of the target potential - are built into the flow. We provide a theoretical sufficient criterion showing that the distribution generated by equivariant normalizing flows is invariant with respect to these symmetries by design. Furthermore, we propose building blocks for flows which preserve symmetries which are usually found in physical/chemical many-body particle systems. Using benchmark systems motivated from molecular physics, we demonstrate that those symmetry preserving flows can provide better generalization capabilities and sampling efficiency.

Aaditya Baranwal, Shruti Vyas

We introduce ChemPro, a progressive benchmark with 4100 natural language question-answer pairs in Chemistry, across 4 coherent sections of difficulty designed to assess the proficiency of Large Language Models (LLMs) in a broad spectrum of general chemistry topics. We include Multiple Choice Questions and Numerical Questions spread across fine-grained information recall, long-horizon reasoning, multi-concept questions, problem-solving with nuanced articulation, and straightforward questions in a balanced ratio, effectively covering Bio-Chemistry, Inorganic-Chemistry, Organic-Chemistry and Physical-Chemistry. ChemPro is carefully designed analogous to a student's academic evaluation for basic to high-school chemistry. A gradual increase in the question difficulty rigorously tests the ability of LLMs to progress from solving basic problems to solving more sophisticated challenges. We evaluate 45+7 state-of-the-art LLMs, spanning both open-source and proprietary variants, and our analysis reveals that while LLMs perform well on basic chemistry questions, their accuracy declines with different types and levels of complexity. These findings highlight the critical limitations of LLMs in general scientific reasoning and understanding and point towards understudied dimensions of difficulty, emphasizing the need for more robust methodologies to improve LLMs.

Kumar Maddina Dinesh, Upadhya Mamatha Sadananda, Yook Se-Jin et al.

Advancements in nanotechnology have revolutionized the field of biomedical applications. Nanoparticles of molybdenum disulphide, copper, silver, aluminium oxide, and carbon nanotubes exhibit significant anticancer and antimicrobial properties. In this study, blood flow through cosine-shaped stenotic arteries was mathematically modelled and examined in an aligned magnetic field, radiation, and nanoparticles. Comparisons were made between the hybrid nanofluid flow in the cosine-shaped stenosis artery and other blood vessels for two cases: Case 1 – Blood+Cu+MOS2+Al2O3\text{Blood}+\text{Cu}+{\text{MOS}}_{\text{2}}+{\text{Al}}_{\text{2}}{\text{O}}_{\text{3}}, and Case 2 – Blood+Ag+SWCNT+MWCNT\text{Blood}+\text{Ag}+\text{SWCNT}+\text{MWCNT}. The flow governing equations are transformed into ODEs and solved numerically using spectral quasi-linearization with MATLAB (SQLM). Expressions for the temperature, velocity profile, and numerical and graphical representations were used to calculate and assess the Nusselt number and skin friction. The investigation was validated by comparing it with the published work. It was found that the Cu+MOS2+Al2O3\text{Cu}+{\text{MOS}}_{\text{2}}+{\text{Al}}_{\text{2}}{\text{O}}_{\text{3}} combination effectively enhanced heat transmission in blood with improved radiation parameters and flow constraints, and the Ag+SWCNT+MWCNT\text{Ag}+\text{SWCNT}+\text{MWCNT} combination effectively enhanced heat transmission in blood with improvement in magnetic parameters. This finding might be helpful in investigations on nano-haemodynamics and the therapy of haemodynamic disorders.

Hardoň Štefan, Kúdelčík Jozef, Janek Marián et al.

Halloysite nanotubes (HNT), as naturally occurring anisotropic nanofillers, were incorporated into a commercial two-component (2C) polyurethane (PU) system to develop multifunctional nanocomposites for electroinsulating applications. The nanocomposites were prepared via the method of direct dispersion. Dielectric, thermal, and mechanical properties were systematically analyzed at weight concentrations of 2 wt%, 5 wt%, and 10 wt% of HNT in the PU matrix. At 5 wt% HNT, an optimal balance was observed: volume resistivity increased nearly 17-fold, dielectric permittivity was enhanced through Maxwell–Wagner–Sillars interfacial polarization, and thermal conductivity rose modestly while maintaining high mechanical integrity. Broadband dielectric spectroscopy, modeled using the Havriliak–Negami function, showed broadened relaxation dynamics associated with filler–matrix interfaces. Incorporation of 10 wt% HNT caused agglomeration, reducing property uniformity. The results demonstrate that controlled integration of HNT into cold-curing 2C PU systems yields cost-effective, sustainable, and high-performance nanodielectrics, advancing their potential use in high-voltage insulation, aerospace encapsulation, and battery module safety.

Xinglong Zhang, Huiwen Tan, Jingyi Liu et al.

CHEMSMART (Chemistry Simulation and Modeling Automation Toolkit) is an open-source, Python-based framework designed to streamline quantum chemistry workflows for homogeneous catalysis and molecular modeling. By integrating job preparation, submission, execution, results analysis, and visualization, CHEMSMART addresses the inefficiencies of manual workflow management in computational chemistry by ensuring seamless interoperability with quantum chemistry packages and cheminformatics platforms. Its modular architecture supports automated job submission and execution tasks for geometry optimization, transition state searches, thermochemical analysis, and non-covalent interaction plotting, while auxiliary scripts facilitate file conversion, data organization, and electronic structure analysis. Future developments aim to expand compatibility with additional software, incorporate QM/MM and classical MD, and align with FAIR data principles for enhanced reproducibility and data reuse. Available on GitHub, CHEMSMART empowers researchers with a robust, user-friendly platform for efficient and reproducible computational chemistry.

Silvia SATO-SOTO, Shota SATO, Seiya TSUJIMURA

Microbial fuel cells (MFC) are technologies that use microorganisms that transfer electrons to the anode, which flows to the cathode to find a final electron acceptor. Oxygen (O2) is the most widely used electron acceptor as it can diffuse through air-cathodes in single-chamber MFCs. However, microorganisms need neutral to slightly acid pH to survive, which is detrimental to the oxygen reduction reaction (ORR). Therefore, catalysts are needed at the air-cathodes to sustain a stable operation of single-chamber MFCs. Here, we report that the use of small amount (0.15 mg cm−2) of a Fe-N-C catalyst with carbon black in air-cathodes promote the ORR in neutral media and can sustain a stable MFC operation, keeping cell voltages of 0.3 V for 8 days.

Paul J. Robinson, Adam Rettig, Hieu Q. Dinh et al.

Molecular quantum chemistry has seen enormous progress in the last few decades thanks to the more advanced and sophisticated numerical techniques and computing power. Following the recent interest in extending these capabilities to condensed-phase problems, we summarize basic knowledge of condensed-phase quantum chemistry for ones with experience in molecular quantum chemistry. We highlight recent efforts in this direction, including solving the electron repulsion integrals bottleneck and implementing hybrid density functional theory and wavefunction methods, and lattice dynamics for periodic systems within atom-centered basis sets. Many computational techniques presented here are inspired by the extensive method developments rooted in quantum chemistry. In this Focus Article, we selectively focus on the computational techniques rooted in molecular quantum chemistry, emphasize some challenges, and point out open questions. We hope our perspectives will encourage researchers to pursue this exciting and promising research avenue.

D.D. Tumarkina, O.Ya. Butkovskii, A.V. Bolachkov et al.

The paper presents experiments on crystallization from a melt with an analysis of the morphology of the emerging crystal structures, showing examples of the formation of dendritic crystals. Using energy dispersive X-ray analysis, studies of the microelement analysis of the areas of effect of two pulsed laser beams on the surface of stainless steel have been carried out for irradiation parameters corresponding to the appearance of dendritic structures in the area of effect. It is shown that in the dendritic regions concentrations of all the components of AISI 304 stainless steel are equalized. Estimation of the entropy of mixing from experimental data showed that in the area of surface dendrites or their accumulations, the surface entropy of mixing corresponded to its value for a high-entropy alloy. Based on the maximum entropy production principle, the phase transition temperature was calculated. Although dendritic crystallization should reduce the entropy of the system, experiments show that the entropy of the alloy increases. Preliminarily it can be concluded that this process is associated with a high oxygen content in the region of dendritic crystal formation after laser irradiation. The results presented in this work allow us to conclude that the formation of structures with complex morphology occurs after thermal oxidative ablation.

Tudor Vasiliu, Francesca Mocci, Aatto Laaksonen et al.

Polyamines have important roles in the modulation of the cellular function and are ubiquitous in cells. The polyamines putrescine2+, spermidine3+, and spermine4+ represent the most abundant organic counterions of the negatively charged DNA in the cellular nucleus. These polyamines are known to stabilize the DNA structure and, depending on their concentration and additional salt composition, to induce DNA aggregation, which is often referred to as condensation. However, the modes of interactions of these elongated polycations with DNA and how they promote condensation are still not clear. In the present work, atomistic molecular dynamics (MD) computer simulations of two DNA fragments surrounded by spermidine3+ (Spd3+) cations were performed to study the structuring of Spd3+ “caged” between DNA molecules. Microsecond time scale simulations, in which the parallel DNA fragments were constrained at three different separations, but allowed to rotate axially and move naturally, provided information on the conformations and relative orientations of surrounding Spm3+ cations as a function of DNA-DNA separation. Novel geometric criteria allowed for the classification of DNA-Spd3+ interaction modes, with special attention given to Spd3+ conformational changes in the space between the two DNA molecules (caged Spd3+). This work shows how changes in the accessible space, or confinement, around DNA affect DNA-Spd3+ interactions, information fundamental to understanding the interactions between DNA and its counterions in environments where DNA is compacted, e.g. in the cellular nucleus.

Liming Zhang, Jingwen Yu, Mingmei Yang et al.

Janus materials have distinct surfaces on their opposite faces. Graphene, a two-dimensional giant molecule, provides an excellent candidate to fabricate the thinnest Janus discs and study the asymmetric chemistry of atomic-thick nanomembranes using covalent chemical functionalisation. Here we present the first experimental realisation of nonsymmetrically modified single-layer graphene—Janus graphene—which is fabricated by a two-step surface covalent functionalisation assisted by a poly(methyl methacrylate)-mediated transfer approach. Four types of Janus graphene are produced by co-grafting of halogen and aryl/oxygen-functional groups on each side. Chemical decorations on one side are found to be capable of affecting both chemical reactivity and physical wettability of the opposite side, indicative of communication between the two grafted groups. This novel asymmetric structure provides a platform for theoretical and experimental studies of two-dimensional chemistry and graphene devices with multiple functions. Janus materials have distinct chemical functionalities on opposite faces. Zhang et al.report that a two-step covalent functionalisation and poly(methyl methacrylate)-mediated transfer process facilitates the synthesis of nonsymmetrically modified single-layer graphene.

Breno Nascimento Ciribelli, F. Colmati, E. C. Souza

Walther Hermann Nernst received the Nobel Prize in Chemistry in 1920 for the formulation of the third law of thermodynamics, thus celebrating a century in this 2020 year. His work helped the establishment of modern physical chemistry, since he researched into fields, such as thermodynamics and electrochemistry, in which the Nernst equation is included. This paper reports on several experiments that used a Daniell galvanic cell working in different electrolyte concentrations for comparing results with the theoretical values calculated by the Nernst equation. The concentration and activity coefficients values employed for zinc sulfate and copper electrolytes showed activity can replaces concentrations in thermodynamic functions, and the results are entirely consistent with experimental data. The experimental electromotive force from standard Daniell cell, for ZnSO4 and CuSO4, with unitary activity and in different concentrations at room temperature is in agreement with those from theoretical calculations. Cu2+ ion concentrations and temperature were simultaneously varied; however, the cell potential cannot be included in calculations of Nernst equation for different temperatures than 25 °C because the standard potential value was set at 25 °C. The cell potential decreases drastically when the Cu2+ concentration was reduced and the temperature was above 80 oC.

Yusuke MORIKAWA, Yuki YAMADA, Kyosuke DOI et al.

Hard carbon is widely studied as a promising negative electrode in sodium-ion batteries. To achieve its stable charge-discharge reaction, a fluorine-rich passivation film arising from a fluorinated salt or solvent in an electrolyte was demonstrated to be effective, but its essential role remained unclear. Here, we report a sodium tetraphenylborate (NaBPh4)/1,2-dimethoxyethane (DME) electrolyte that is free from fluorine but enables the highly stable and high-rate charge-discharge cycling of hard carbon electrodes as compared to other combinations of Na salts and solvents. Surface analysis of the cycled electrode shows that the NaBPh4 is not decomposed during the cycle and that solid electrolyte interphase (SEI) is derived from DME. Hence, fluorine-based components are not indispensable to stabilize the hard carbon/electrolyte interface. The DME-derived SEI, though containing no F component, can highly stabilize the interface to enable the reversible and high-rate cycling of hard carbon.

Xiong Zhang, Jiewen Li, Xingwen Zheng et al.

The anticorrosion properties of 1-butyl-3-methyl-1H-benzimidazolium iodide (BMBM) for 2205 duplex stainless steel in 1.0 M HCl solution has been evaluated by electrochemical techniques (potentiodynamic polarization and electrochemical impedance spectroscopy) and scanning electron microscopy. The effect of temperature and concentration on the inhibition efficiency have also been studied. The results reveal that BMBM is a mixed-type inhibitor whose adsorption obeys the Langmuir adsorption isotherm. The inhibition efficiency increased with increase in concentration, but decreased when the temperature was raised. The results obtained from kinetic analysis were compared with those of electrochemical techniques and they confirmed that BMBM is an effective green corrosion inhibitor for 2205 duplex stainless steel in 1.0 M HCl.

Kun Wang, Yubiao Wang, Qi Shen

The turbulated cooling channel in turbine blades is a typical special-shaped inner wall structure that can significantly enhance the cooling effect of gas turbine blades. The use of electrochemical machining to manufacture cooling channels has the advantages of high efficiency and no residual stress. However, the stray current removal cannot be completely avoided using liquid electrolyte. Consequently, an ideal inner wall structure, consisting of a turbulated cooling channel, cannot be obtained. In this paper, an electrochemical machining method is proposed in which a gelatinous electrolyte is used to meet the machining requirements. Through the cross-linking of polymers, a liquid electrolyte is filled into the gaps of the gelatinous network structure to form a gelatinous electrolyte. The stray current removal due to the flow of the liquid electrolyte is avoided. A gelatinous electrode of diameter 5 mm was prepared. A turbulated cooling channel with a rectangular cross section and rib height of 0.8 mm on nickel is obtained. The profile view of the experimentally prepared turbulated cooling channel structure has a rectangular cross section and maintains good straightness. The proposed machining method is expected to be widely applicable to electrochemical machining of the inner wall structures in narrow spaces.

Jesús Pérez-Ríos

Impurity physics is a traditional topic in condensed matter physics that nowadays is being explored in the field of ultracold gases. Among the different classes of impurities, we focus on charged impurities in an ultracold bath. When a single ion is brought in contact with an ultracold gas it is subjected to different reactive processes that can be understood from a cold chemistry approach. In this work, we present an outlook of approaches for the dynamics of a single ion in a bath of ultracold atoms or molecules, complementing the usual many-body approaches characteristic of impurity physics within condensed matter physics. In particular, we focus on the evolution of a charged impurity in different baths, including external time-dependent trapping potentials and we explore the effect of the external laser sources present in ion-neutral hybrid traps into the lifetime of an impurity.

Liang Huang, Yan Cao, Feng Jia et al.

With the widespread application of non-conducting tough materials, such as glass in MEMS recent years, many difficulties have arisen in the processing of these kind of material with eigen-structure characteristics. In this paper, based on the technical advantages of electrochemical discharge machining, the mechanism of tool electrode structure and process parameters for the stability of gas film, processing efficiency and forming quality is analysed, and the machining of a glass micro-array hole is accomplished by obtaining the optimal process parameters.