Pairs Of Atoms Research Articles

The Aromaticity of Osmapentalenes Derivatives. An Analysis Based on Electron-delocalization Indices.

A systematic investigation of the aromatic features of the electronic structures of a family of recently synthesized osmapentalene derivatives has been carried by means of indices derived from the calculated one-electron density matrix of the corresponding geometry optimized compounds, and complemented by the analysis of the valence molecular orbitals and the delocalized bonding units emerging from the adaptive natural density partitioning method. The calculated delocalization indices between consecutive atom pairs, and normalized multicenter indices are very suggestive of the aromatic character of the equatorial fused carbon rings (except triangular ones) for all the members of the family. Since the electron-delocalization based indices allow precise quantification of the aromaticity, differences of the aromatic character among the various members have also been highlighted, and have been found to be consistent with the magnetic based criteria indices reported earlier. Finally, the valence molecular orbitals along with the delocalized bonding units of the adaptive natural density partitioning indicate that the aromaticity of these compounds is sustained by either 10 or 14 π electrons, which satisfy the Hückel aromatic electron counting rule.

Dynamics of entanglement of qubits in the three-qubit Tavis — Cummings model with dipole-dipole interaction

The article studies the dynamics of pairwise entanglement of three qubits, two of which are trapped in a resonator and interact with a single-mode ideal resonator through single-photon transitions, and the third qubit is outside the resonator. This takes into account the dipole-dipole coupling between the isolated qubit and the qubit in the resonator. We have found a solution to the quantum nonstationary Schrodinger equation for the total wave function of the system for the initial separable and biseparable states of qubits and the thermal initial state of the resonator field. Using these solutions, the criterion of entanglement of qubit pairs - negativity is calculated. The results of numerical simulation of the negativity criterion have shown that the including of a small dipole-dipole coupling between an isolated and one of the trapped qubits can lead to significant entanglement of qubit pairs for all initial states. There is a transition of entanglement from one pair of atoms to other pairs of atoms during the evolution of the system. It is also shown that for some separable and biseparable states, the dipole-dipole interaction can suppress the effect of sudden death of entanglement

Copper Atom Pairs Stabilize *OCCO Dipole Toward Highly Selective CO2 Electroreduction to C2H4

AbstractDeeply electrolytic reduction of carbon dioxide (CO2) to high‐value ethylene (C2H4) is very attractive. However, the sluggish kinetics of C−C coupling seriously results in the low selectivity of CO2 electroreduction to C2H4. Herein, we report a copper‐based polyhedron (Cu2) that features uniformly distributed and atomically precise bi‐Cu units, which can stabilize *OCCO dipole to facilitate the C−C coupling for high selective C2H4 production. The C2H4 faradaic efficiency (FE) reaches 51 % with a current density of 469.4 mA cm−2, much superior to the Cu single site catalyst (Cu SAC) (~0 %). Moreover, the Cu2 catalyst has a higher turnover frequency (TOF, ~520 h−1) compared to Cu nanoparticles (~9.42 h−1) and Cu SAC (~0.87 h−1). In situ characterizations and theoretical calculations revealed that the unique Cu2 structural configuration could optimize the dipole moments and stabilize the *OCCO adsorbate to promote the generation of C2H4.

Comparing SMILES and SELFIES tokenization for enhanced chemical language modeling

Life sciences research and experimentation are resource-intensive, requiring extensive trials and considerable time. Often, experiments do not achieve their intended objectives, but progress is made through trial and error, eventually leading to breakthroughs. Machine learning is transforming this traditional approach, providing methods to expedite processes and accelerate discoveries. Deep Learning is becoming increasingly prominent in chemistry, with Convolutional Graph Networks (CGN) being a key focus, though other approaches also show significant potential. This research explores the application of Natural Language Processing (NLP) to evaluate the effectiveness of chemical language representations, specifically SMILES and SELFIES, using tokenization methods such as Byte Pair Encoding (BPE) and a novel approach developed in this study, Atom Pair Encoding (APE), in BERT-based models. The primary objective is to assess how these tokenization techniques influence the performance of chemical language models in biophysics and physiology classification tasks. The findings reveal that APE, particularly when used with SMILES representations, significantly outperforms BPE by preserving the integrity and contextual relationships among chemical elements, thereby enhancing classification accuracy. Performance was evaluated in downstream classification tasks using three distinct datasets for HIV, toxicology, and blood–brain barrier penetration, with ROC-AUC serving as the evaluation metric. This study highlights the critical role of tokenization in processing chemical language and suggests that refining these techniques could lead to significant advancements in drug discovery and material science.

Electronic Structure Simulations of the Platinum/Support/Ionomer Interface in Proton Exchange Membrane Fuel Cells

ABSTRACTIn this work, we present electronic structure calculations to quantify and rationalize the interactions between catalyst, support, ionomer, and active molecular species in proton exchange membrane fuel cells. Quantifying interaction energies and their scaling with size allows us to rationalize and compare the fundamental driving forces behind structure formation and material properties. Our basic approach involves simplifying the most important interactions between different components using smaller model systems, such as limited‐size platinum nanoparticles, polyaromatic hydrocarbons (graphene flakes), and fragments of various functional units of the Nafion ionomer while applying unbiased first‐principles (density functional theory) simulation methods. To guide this quantification, we propose an analysis based on the linear dependence of interaction energy on the number of interacting atom pairs in the interface. This enables us to compare and categorize interactions between catalyst, ionomer, and support with interactions like catalyst–reactant and catalyst–catalyst poison.

Surface electronic fine-perturbation driven by distal atom coupling at W-Se pair sites for enhanced ammonia synthesis

Engineering single-atom electrocatalysts (SACs) of geometries and electronic structures at atomic level to overcome the critical trade-off in catalytic performance remains a significant challenge. Here, we report a novel metal–nonmetal pair sites with non-bonding interaction to achieve dual enhancements of activity and selectivity for nitrogen reduction reaction (NRR). The stable non-bonding structure of W-Se atom pairs on C3N4 support (W-SeC3N4) was engineered by photo-assisted cryogenic reduction. Distal Se-atom coupling drives a fine-tuning of surface-localized electronic state on center W-atom through genuine chemical interaction and modulates the adsorption energies of intermediates like *NNH, *NH and *NH2. W-SeC3N4 thus demonstrates a NH3 yield rate of 74.6 ug h−1 mgcat−1 and >38.2 % selectivity, surpassing all current non-precious metal SACs. Our work supplies an advanced strategy for the rational design of SACs in complex chemical reactions involving multi-step intermediates.

Structural Features Investigation of a Highly Dispersed NiO–SiO<sub>2</sub> Catalyst by X-Ray Analysis of the Atomic Pair Distribution Function

In the present work NiO and NiO–SiO2 were investigated by X-ray diffraction and radial atomic pair distribution methods. By X-ray diffraction method, it was determined that the NiO particle sizes have coherent scattering region of more than 100 nm, while the NiO–SiO2 sample has a particle size of about 2–3 nm. At the same time, full-profile Rietveld simulation does not describe the effects observed on diffraction: the asymmetry of peaks, the appearance of an additional shoulder of peak 111 in the area of small angles, so the radial atomic pair distribution method was used to analyze the structure. During the simulation of the experimental atomic pair distribution curve, 3 different models were used: pure NiO, a mixture of NiO and Ni2SiO4, and a modified NiO model with Si embedded in the lattice. The latter model was created based on the assumption of silicon incorporation into the NiO structure, which can be evidenced by X-ray diffraction data. According to the results of radial atomic pair distribution modeling it is the latter model that gives the best description of the observed effects: significantly increased unit cell parameter, compared to the sample without SiO2 addition, as well as decreased metal cation–oxygen distances in the structure, while cation–cation distances are increased.

Novel Amorphous Nitride‐Halide Solid Electrolytes with Enhanced Performance for All‐Solid‐State Batteries

Solid electrolytes (SEs) in all‐solid‐state batteries (ASSBs) are garnering considerable attention for their potential applications in next‐generation energy storage systems. Amorphous SEs with dual‐anion hold great promise for achieving favorable performance, such as high ionic conductivity and good compatibility with electrodes within ASSBs. Here, we discover a family of amorphous nitride‐halide SEs, Li3xMClyNx (M = Ta or La, 1 ≤ 3x ≤ 1.4, y = 5 or 3), which can achieve ionic conductivities up to 7.34 mS cm‒1 at 30 °C. The amorphous properties and local structures are investigated using powder X‐ray diffraction, cryogenic transmission electron microscopy, and atomic pair distribution function analysis. Impressively, ASSBs employing amorphous Li3xTaCl5Nx have demonstrated good performance at high rates and charging voltages, as well as at low temperature.

Novel Amorphous Nitride-Halide Solid Electrolytes with Enhanced Performance for All-Solid-State Batteries.

Solid electrolytes (SEs) in all-solid-state batteries (ASSBs) are garnering considerable attention for their potential applications in next-generation energy storage systems. Amorphous SEs with dual-anion hold great promise for achieving favorable performance, such as high ionic conductivity and good compatibility with electrodes within ASSBs. Here, we discover a family of amorphous nitride-halide SEs, Li3xMClyNx (M = Ta or La, 1 ≤ 3x ≤ 1.4, y = 5 or 3), which can achieve ionic conductivities up to 7.34 mS cm‒1 at 30 °C. The amorphous properties and local structures are investigated using powder X-ray diffraction, cryogenic transmission electron microscopy, and atomic pair distribution function analysis. Impressively, ASSBs employing amorphous Li3xTaCl5Nx have demonstrated good performance at high rates and charging voltages, as well as at low temperature.

Unleashed Remarkable Energy Storage Performance in Bi0.5K0.5TiO3-based Relaxor Ferroelectrics by Local Structural Fluctuation.

Dielectric capacitors harvest energy through an electrostaticprocess, which enables an ultrafast charging-discharging rate and ultrahigh power density. However, achieving high energy density (Wrec) and efficiency (η) simultaneously, especially when preserving them across a wide frequency/temperature range or cycling numbers, remains challenging. In this work, by especially introducing NaTaO3 into the representative ferroelectric relaxor of Bi0.5K0.5TiO3-Bi0.5Na0.5TiO3 and leveraging the mismatch between B-site atoms, we proposed a method of enhancing local structural fluctuation to refine the polar configuration and to effectively improve its overall energy-storage performances. As a consequence, the ceramic exhibits an ultrahigh Wrec of 15.0 J/cm3 and high η up to 80%, along with a very wide frequency stability of 10 - 200 Hz and extensive cycling number up to 108. In-depth local structure and chemical environment investigations, consisting of atom-scale electron microscopy, neutron total scattering, and solid-state nuclear magnetic resonance, reveal that the randomly distributed A/B-site atom pairs emerge in the system, leading to the evident local structural fluctuations and concomitant polymorphic polar nanodomains. These key ingredients contribute to the large polarization, minimal hysteresis, and high breakdown strength, thereby promoting energy-storage performances. This work opens a new path for designing high-performance dielectric capacitors via manipulating local structural fluctuations.

Shannon entropy variation as a global indicator of electron density contraction at interatomic regions in chemical reactions.

The negative of the Shannon entropy derivative is proposed to account for electron density contraction as the chemical bonds are breaking and forming during a chemical reaction. We called this property the electron density contraction index, EDC, which allows identifying stages in a reaction that are dominated by electron contraction or expansion. Four different reactions were analyzed to show how the EDC index changes along the reaction coordinate. The results indicate that the rate of change of Shannon entropy is directly related to the rate of change of the electron density at the bond critical points between all the atomic pairs in the molecular systems. It is expected that EDC will complement the detailed analysis of reaction mechanisms that can be performed with the theoretical tools available to date. Density functional theory calculations at the B3LYP/6-31G(d,p) level of theory were carried out using Gaussian 16 to analyze the reaction mechanisms of the four reactions studied. The reaction paths were obtained via the intrinsic reaction coordinate method, which served as the reaction coordinate to obtain the reaction force and the EDC profiles in each case. Shannon entropy and electron density at the bond critical points were calculated using the Multiwfn 3.7 package.

Recent Achievements in Heterogeneous Bimetallic Atomically Dispersed Catalysts for Zn-Air Batteries: A Minireview.

Rechargeable Zn-air batteries (ZABs) hold promise as the next-generation energy-storage devices owing to their affordability, environmental friendliness, and safety. However, cathodic catalysts are easily inactivated in prolonged redox potential environments, resulting in inadequate energy efficiency and poor cycle stability. To address these challenges, anodic active sites require multiple-atom combinations, that is, ensembles of metals. Heterogeneous bimetallic atomically dispersed catalysts (HBADCs), consisting of heterogeneous isolated single atoms and atomic pairs, are expected to synergistically boost the cyclic oxygen reduction and evolution reactions of ZABs owing to their tuneable microenvironments. This minireview revisits recent achievements in HBADCs for ZABs. Coordination environment engineering and catalytic substrate structure optimization strategies are summarized to predict the innovation direction for HBADCs in ZAB performance enhancement. These HBADCs are divided into ferrous and nonferrous dual sites with unique microenvironments, including synergistic effects, ion modulation, electronic coupling, and catalytic activity. Finally, conclusions and perspectives relating to future challenges and potential opportunities are provided to optimise the performance of ZABs.

Data quality in laboratory convergent-beam X-ray total scattering

Measurement of laboratory atomic pair distribution function data has improved with contemporary X-ray sources, optics and detectors, with acquisition times of the order of minutes for ideal samples. This paper examines resolution effects in pair distribution function data obtained using a convergent-beam configuration and an Ag X-ray tube from standard silicon powder and from 10 nm BaTiO3 nanocubes. The elliptical multilayer X-ray mirror reflects a non-trivial X-ray spectrum and introduces resolution effects not commonly treated in ordinary parafocusing divergent-beam laboratory diffraction. These resolution effects are modeled using the fundamental parameters approach, and the influence this has on interpretation and modeling of the resulting reduced atomic pair distribution function data is demonstrated.

Precise Synthesis of Dual-single-atom Electrocatalysts through Pre-coordination-directed in situ Confinement for CO2Reduction.

Dual-single-atom catalysts (DSACs) are the next paradigm shift in single-atom catalysts because of the enhanced performance brought about by the synergistic effects between adjacent bimetallic pairs. However, there are few methods for synthesizing DSACs with precise bimetallic structures. Herein, a pre-coordination strategy is proposed to precisely synthesize a library of DSACs. This strategy ensures the selective and effective coordination of two metals via phthalocyanines with specific coordination sites, such as -F- and -OH-. Subsequently, in-situ confinement inhibits the migration of metal pairs during high-temperature pyrolysis, and obtains the DSACs with precisely constructed metal pairs. Despite changing synthetic parameters, including transition metal centers, metal pairs, and spatial geometry, the products exhibit similar atomic metal pairs dispersion properties, demonstrating the universality of the strategy. The pre-coordination strategy synthesized DSACs shows significant CO2 reduction reaction performance in both flow-cell and practical rechargeable Zn-CO2 batteries. This work not only provides new insights into the precise synthesis of DSACs, but also offers guidelines for the accelerated discovery of efficient catalysts.

Precise Synthesis of Dual‐single‐atom Electrocatalysts through Pre‐coordination‐directed in situ Confinement for CO2 Reduction

Dual‐single‐atom catalysts (DSACs) are the next paradigm shift in single‐atom catalysts because of the enhanced performance brought about by the synergistic effects between adjacent bimetallic pairs. However, there are few methods for synthesizing DSACs with precise bimetallic structures. Herein, a pre‐coordination strategy is proposed to precisely synthesize a library of DSACs. This strategy ensures the selective and effective coordination of two metals via phthalocyanines with specific coordination sites, such as –F– and –OH–. Subsequently, in‐situ confinement inhibits the migration of metal pairs during high‐temperature pyrolysis, and obtains the DSACs with precisely constructed metal pairs. Despite changing synthetic parameters, including transition metal centers, metal pairs, and spatial geometry, the products exhibit similar atomic metal pairs dispersion properties, demonstrating the universality of the strategy. The pre‐coordination strategy synthesized DSACs shows significant CO2 reduction reaction performance in both flow‐cell and practical rechargeable Zn‐CO2 batteries. This work not only provides new insights into the precise synthesis of DSACs, but also offers guidelines for the accelerated discovery of efficient catalysts.

Cobalt(II) Complex Constructed from Pyrazinecarboxamide and Aromatic Carboxylic Acid: Synthesis, Single Crystal XRD Along with Computational Study

A cobalt (II) mononuclear complex was synthesized by two-nitrobenzoic acid and pyrazine-two- carboxamide ligands in the presence of sodium bicarbonate and aqueous solution of cobalt acetate tetrahydrate. The synthesized cobalt(II) complex was characterized by single crystal X-rays diffraction. The coordination geometry of the cobalt complex was octahedral with water molecules occupying the axial sites. A lot of intermolecular interactions were in response to stabilize the supramolecular assembly which were inspected by Hirshfeld surface analysis. Enrichment ratios were calculated to find the pair of atoms having the highest propensity to form crystal packing interactions. Void analysis was conducted to forecast how the crystal would respond to applied stress. Interaction energy calculations were carried out using the B3LYP/6-31G(d,p) electron density model to identify which energy types most significantly contributed to the supramolecular assembly. Moreover, the energy data obtained from DFT calculations showed an average level of stability of the molecule. The moderate HOMO-LUMO energy gap suggested reactivity, while a high electrophilicity index indicates a strong tendency for electron-accepting reactions.

Improvement of strength in low-carbon Nb–Ti weathering steel through Ce microalloying

In this study, a high-strength low carbon Nb–Ti containing weathering steel was developed. The steel achieved a yield strength of 824.4 MPa and an elongation of 24.4% with the addition of 0.030% Ce as a microalloying element. Precipitation strengthening and dislocation strengthening contributed nearly 60% to the yield strength of the steel. The effects of Ce on the dissolution and precipitation behavior of microalloying elements were analyzed through experimental research and first-principles calculations. Additionally, the associated strengthening mechanisms were elucidated. The findings revealed that the Ce–Nb pairs within the 2 to 7 nearest-neighbor configuration in face-centered cubic Fe exhibited a mutual attraction. This attraction promoted the dissolution of microalloyed carbonitrides, leading to a reduction in the volume fraction of precipitates with diameters above 150 nm from 1.3% to 0.62%. Conversely, in the body-centered cubic Fe structure, Ce–Nb atom pairs were mutually repulsive across all configurations. During the coiling process, the addition of Ce increased the formation of nanoprecipitates in the 0.030% Ce–Nb–Ti weathering steel. Particularly, the volume fraction of precipitates with diameters ranging from 20 to 150 nm in the steel increased from 1.6% to 2.7%, while the fraction of nanoprecipitates also increased from 0.051% to 0.31%. The nanoprecipitates formed within the dislocation substructure of the ferrite significantly enhanced steel strength but reduced its plasticity. Additionally, the addition of Ce led to the formation of numerous fine cementite particles in the localized areas of the steel matrix, which contributed up to 49.2 MPa to the overall strength of the steel.

Tuning the Inter‐Metal Interaction between Ni and Fe Atoms in Dual‐Atom Catalysts to Boost CO2 Electroreduction

AbstractDual‐atom catalysts (DACs) are promising for applications in electrochemical CO2 reduction due to the enhanced flexibility of the catalytic sites and the synergistic effect between dual atoms. However, precisely controlling the atomic distance and identifying the dual‐atom configuration of DACs to optimize the catalytic performance remains a challenge. Here, the Ni and Fe atomic pairs were constructed on nitrogen‐doped carbon support in three different configurations: NiFe‐isolate, NiFe‐N bridge, and NiFe‐bonding. It was found that the NiFe‐N bridge catalyst with NiN4 and FeN4 sharing two N atoms exhibited superior CO2 reduction activity and promising stability when compared to the NiFe‐isolate and NiFe‐bonding catalysts. A series of characterizations and density functional theory calculations suggested that the N‐bridged NiFe sites with an appropriate distance between Ni and Fe atoms can exert a more pronounced synergy. It not only regulated the suitable adsorption strength for the *COOH intermediate but also promoted the desorption of *CO, thus accelerating the CO2 electroreduction to CO. This work provides an important implication for the enhancement of catalysis by the tailoring of the coordination structure of DACs, with the identification of distance effect between neighboring dual atoms.

Effect of fly ash and nano Silica on the formation and evolution of Calcium Silicate Hydrate in Portland Cement during hydration process

Recently, the trend of replacing cement with mineral admixtures in concrete has witnessed increasing interest in the construction industry due to the reduction in embodied energy and CO2 emissions. However, the addition of these admixtures in Portland Cement (PC) affected the formation as well as the structure of the hydration product Calcium-Silicate-Hydrate (C-S-H), which is reflected in the mechanical and durability properties of cement concrete. In the present study, nano-silica (NS) and a mixture of fly ash (FA) and NS were replaced into PC (PC + 0.5 % NS, PC + 1 % NS, PC + 0.5 % NS + 20 % FA and PC + 1 % NS + 40 % FA) to systematically study the formation and structural evolution of hydration products, namely C-S-H, at atomic and micro-scales at the early stage of hydration (3 days) and a later stage of hydration (90 days). The formation and structure of C-S-H were analyzed to correlate the microstructure development by using XRD, Rietveld technique, FESEM, TEM, FTIR and nano-scale mechanical properties by employing the nanoindentation techniques. Atomic Pair Distribution Function (PDF) is used to understand the effect of admixtures on the C-S-H structure from atomic point of view. PDF shows the structural modification of C-S-H such as different polyhedral, separation of intralayer/interlayer, pair/bond length, coordination number of atoms corresponding to the addition of additives with hydration age. Also, porosity measurements show increasing or decreasing porosity during hydration with additives. It is observed that the contribution of low-density C-S-H (LD C-S-H) is greater than that of high-density C-S-H (HD C-S-H) in the beginning days, whereas HD C-S-H more than LD C-S-H in the latter days of hydration. The elastic modulus increased from 15.44 GPa to 19.82 GPa and the hardness decreased from 0.41 GPa to 0.35 GPa of LD C-S-H in early days, whereas elastic modulus decreased from 34.84 GPa to 29.33 GPa and the hardness increased from 0.75 GPa to 0.83 GPa of HD C-S-H in the latter stage due to addition of additives. However, both increased for LD C-S-H and HD C-S-H for each corresponding mixture during hydration. The present study reported the formation and microstructural modifications of C-S-H and the correlation with nano-mechanical properties due to addition of nano or micro-sized admixtures (nano silica and fly ash) in the cement system. This correlation helps to develop low-energy cement composites by tailoring cement systems with desired properties.

Study of molecular interaction between benzaldehyde and methanol using microwave dielectric relaxation spectroscopy and radial distribution function

A microwave dielectric relaxation study was conducted for mixtures of benzaldehyde (BZ) and methanol (MeOH) over a frequency range of 200 MHz to 20 GHz at seven different temperatures, ranging from 293.15 K to 323.15 K. The dielectric relaxation parameters, obtained through a fitting process, were used to examine their dependence on concentration and temperature. Thermodynamic parameters, such as Gibbs free energy (ΔG), molar enthalpy of activation (ΔH), and molar entropy of activation (ΔS), were evaluated using the temperature dependence of the dipolar relaxation time. The study provided valuable insights into the molecular interactions and dynamic behavior of the components in the binary mixture system. Additionally, a molecular dynamics (MD) simulation study was conducted on the binary mixture of BZ and MeOH to determine the Radial Distribution Function (RDF) and coordination number for different pairs of molecules and atoms, which revealed information about the binding and arrangement of the local structure.