Atomic Volume Research Articles

HP8-to-cP4 structural transition in Ni3In compounds at high temperature and pressure: Theoretical assessment of compression and phase stability information

According to Webb et al. (1986) by heating the Ni3In (hP8) compound at 800–1200 °C under a pressure (P) of 6.5 GPa, a cP4 phase was formed, which reverted to hP8 when annealed at low pressure. A striking X-ray result is that the atomic volume (V) of cP4 was higher than that of hP8. Webb et al. determined the V versus P relations in samples quenched to room temperature and reported that the compressibility of the cP4 phase was significantly larger than that of the hP8 phase. These various findings have been theoretically analyzed in the current work by using ab initio density-functional-theory (DFT) calculations, including an account of the vibrational and electronic contributions to the thermodynamic properties. Calculations of the V versus P relations are used to reassess the compressibility relation between the cP4 and hP8 phases, and Gibbs energy calculations to characterize the relative stability of these structures. In particular, detailed comparisons are reported with the only information available on the thermal properties of the hP8 phase, viz., the Gibbs energy estimates obtained in CALPHAD-type phenomenological modeling of the Ni–In equilibrium diagram. The key qualitative result of the current work is that cP4 should be considered as a high-temperature phase, which might be stabilized by heating to the temperature chosen to anneal the hP8 material under pressure. On this basis it is suggested that the seemingly anomalous relative stability relations discussed by Webb et al. might be a consequence of considering only the effect of pressure on the cP4/hP8 relative phase stability.

Mechanism of Negative Thermal Expansion in Monoclinic Cu2P2O7 from First Principles.

Negative thermal expansion (NTE) materials generally have high-symmetry space groups, large average atomic volumes, and corner-sharing octahedral and tetrahedral coordination structures. By contrast, monoclinic α-Cu2P2O7, which has a small average atomic volume and edge-sharing structure, has been reported to exhibit NTE, the detailed mechanism of which is unclear. In this study, we investigate the A2B2O7 polymorphs and analyze the NTE behavior of α-Cu2P2O7 using first-principles lattice-dynamics calculations. From the polymorphism investigation in 20 A2B2O7 compounds using 6 representative crystal structures, small A and B cationic radii are found to stabilize the α-Cu2P2O7-type structure. We then analyze the NTE behavior of α-Cu2P2O7 using quasi-harmonic approximation. Our calculated thermal expansion coefficients and anisotropic atomic displacement parameters were in good agreement with those of the experimental reports at low temperatures. From the mode-Grüneisen parameter distribution plotted over the entire first-Brillouin zone, we found that the phonon contributing most significantly to NTE emerges not into the special points but between them. In this phonon mode, the O connecting two PO4 tetrahedra rotates, and the Cu and O vibrate perpendicular to the bottom of the CuO5 pyramidal unit, which folds the ac lattice plane. This vibration behavior can explain the experimentally reported anisotropic NTE behavior of α-Cu2P2O7. Our results demonstrate that the most negative mode-Grüneisen parameter contributing to NTE behavior is not always located on high-symmetry special points, indicating the importance of lattice vibration analyses for the entire first-Brillouin zone.

Переменный электрический ток в угольных шахтах: электромагнитная энергия и превращение её в электрический ток

The article addresses the challenge of improving the competence and basic knowledge of specialists working with alternating electric current. The purpose of this work is to explain the magnetic properties of substance, generation of magnetic field and electric current with due account for the known laws of physics and the Quantum theory. We believe that addressing these tasks needs to begin with the energy produced by the magnet. The method of inducing electric energy using magnetic field of a permanent magnet is chosen as the research subject. The historical mythological bases of interpreting the induction of electric energy are shown. Modern instruments prove that the magnetic field is the electromagnetic emissions of magnets. A hypothesis regarding the origin of magnetic properties of substance is developed based on analysis of the known magnetic properties of alpha-iron. Two features of the magnetic properties of substance have been revealed, which differ from Ampere's ideas. The first is the local volume of atoms combined by short-acting covalent bonds, forming a natural crystalline or artificially elongated structure. The second is that the frequency of electromagnetic emissions by the valence electrons of all the atoms in Hertz is approximately the same. The total radiation of energy by all the atoms in local formations generates a magnetic field. The hypothesis is confirmed by circuits and information on instruments that measure the emission of magnets in Hertz. When the energy absorbed by electrons increases, the bond between atoms is broken and magnetic emissions cease. All substances in liquid and solid aggregate state begin to radiate electromagnetic emissions to other substances under the impact of external electromagnetic emissions. This is confirmed by photographic evidence of the performed experiments. A hypothesis is proposed, which differs from the ideas about the movement of free electrons by the fact that the formation of electric current is the result of absorbing electromagnetic emissions of the magnet by valence electrons of the electrical conductor and their transfer into the electric network. The physical phenomena of energy transfer between the transformer windings in an electric circuit prove that electric current is a concentrated flow of electromagnetic emissions, which are a wave form of energy.

Optical red shift spectra in CuxGe32S68-x films for infrared and solar cell window applications

The physical characteristics of Cu-doped ternary glasses have been analyzed. The CuxGe32S68 − x (x = 0.0, 4.0, 7.0, 10.0 and 13.0 at.%) chalcogenide alloys have been manufactured by the conventional melt quenching method. The glass densities (ρ) increase with the Cu amounts, whereas the main atomic volume (Vm) decreases. Transmission and reflectance were measured in the wavelength range of 0.35–2.5 μm. The generated envelops (RM and Rm) of reflectance spectra were used to calculate the film thickness (t), the refractive index (n), and the extinction coefficient (k). With the increase in Cu contents from 0.0 to 13.0 at.%., the n values increased from 2.07 to 2.43, whereas the optical gap (Eg) decreased from 2.81 eV to 2.42 eV. The obtained results were explained in terms of electronic polarizability, plasma frequency, metallization parameter, and refraction losses, which have been calculated to understand the need for amorphous chalcogenide compositions that can be applied for optical device purposes. The effect of Cu content on the non-linear index of refraction (n2) and third-order susceptibility (χ (3)) has been studied. The value of n2 increased from 13.88 × 10−12 to 60.2 × 10−12 esu, whereas the value of χ (3) rose from 7.6 × 10−11 to 38.83 × 10−13 esu with the addition of denser and higher atomic radius elements Cu in the CGS system. Overall, the composition of Cu13Ge32S55 is suitable, as all-optical parameters show the maximum values that can be used for optical device purposes.

Attenuated Total Reflection Infrared and Far-Infrared, and Raman Spectroscopy Studies of Minerals, Rocks, and Biogenic Minerals.

Attenuated total reflection infrared (ATR-IR, 4000-400 cm-1), ATR-far-IR (ATR-FIR, 400-50 cm-1), and Raman spectra (4000-10 cm-1) were measured for calcium carbonate, three kinds of minerals (calcite, aragonite, and quartz), two kinds of rocks (obsidian and pumice), and four kinds of biogenic minerals, i.e., coral (aragonite), Ruditapes philippinarum (aragonite), Meretrix lusoria (aragonite), and Corbicula japonica (aragonite), to investigate the polymorphism of minerals and biogenic minerals, differences in the crystal structure among aragonite and aragonite biogenic minerals, water in the minerals and biogenic minerals, Boson peaks of obsidian and pumice, very small amounts of carotenoids in the three kinds of shells, and so on. In this study, we put some emphasis on the low-frequency region of IR (FIR) and Raman spectra. ATR-FIR spectra were measured down to 50 cm-1 and Raman spectra were obtained down to 10 cm-1. Second derivative spectra were calculated for the FIR spectra. It has been found from the present study that the FIR spectra are the most powerful for exploring polymorphism and differences in the crystal structure among aragonite and aragonite biogenic minerals. A Boson peak, which is a characteristic low-frequency Raman band for amorphous materials, was observed at around 40 cm-1 in the Raman spectra of obsidian and pumice. The Boson peak of pumice is located at a lower frequency by 12 cm-1 than that of obsidian, indicating that the mean atomic volume of pumice is larger than that of obsidian. The present study has revealed that IR spectra are useful to investigate the amounts and structure of fluid and bound water. Moreover, it has also been found that Raman spectra can detect a very tiny amount of carotenoids in the shells due to the resonance Raman effect.

Solubility prediction of drugs in methanol + water mixtures using minimum number of data points: Comparison of various models

ABSTRACT This work reports the ability of cosolvency and activity coefficient models in the prediction of drugs solubility in methanol + water mixtures by choosing a minimum number of experimental data point. For this purpose, the available solubility datasets of drugs were gathered from papers published from 2012 to 2022 and selected seven number of each dataset as the training data whereas the rest of datapoints were the predictive data. Moreover, the effect number of model’s parameters on their accuracies was investigated by training the models with selecting of 12 data points. The results indicated that the accuracy of cosolvency models was better than the activity coefficient models; so that, the simple cosolvency model of Jouyban-Acree which does not require the physicochemical properties of drugs including melting point, fusion enthalpy and also molecular parameters of van der Waals area and volume predicted the drugs solubility with more accuracy (MRDs% of 4.1).

Analyze molecular interaction for mixture of argon and particles with different sizes

This article elaborates on molecular dynamics simulation, which is a technology that supports us in analyzing the structure and dynamics of materials and their properties at a microscopic level. In this article, the molecular dynamics simulation develops on Lennard-Jones potential. The simulation is based on the fundamental understanding between Argon-Argon molecules. The application for running molecular dynamics simulation is Moldy. The Argon particles size is changed by altering van der Waals radius from Lennard-Jones potential parameters, and the mixture of Argon and different sizes particles will be simulated by Moldy. The average potential energy is collected and compared. It discusses how the size of particles affect the average potential energy. Moreover, the trend of potential energy respects to timesteps for each molecule is depicted and compared graphicly by Gnuplot. It discusses how the potential energy changes according to timesteps for different sizes particles. In the end, the result is collected and summarized. It discovers that potential energy increases slowly when particles sizes increase, and the potential energy decreases significantly when particles sizes decrease. In addition, it founds out that molecules with different sizes have a noticeable change initially. Oddly, there is no observation of significant changes in the potential energy of the original molecule. Moreover, the initial decrease for molecules that increase in size is not as significant as that for molecules that decrease in size.

Fine-tuning gas separation performance of intrinsic microporous polyimide by the regulation of atomic-level halogen substitution

The molecular structure of polymers is essential to membrane separation performance. However, the inherent relationship between molecular structure and gas separation performance of polymeric membranes is unclear. Herein, the halogen atoms (F, Cl, and Br) were introduced into intrinsic micropore polyimide (PIM-PI) to precisely regulate its interchain cavity and elucidate the structure-property relationship. Based on the pristine BAPI, the halogen atoms were precisely designed at the ortho position of the amino group and synthesized three PIM-PIs, namely BFPI, BCPI, and BBPI, respectively. Then, it can be found that the packing structure of polymer chains and fine-tuning of fractional free volume (FFV) exhibits a regular trend in halogen-containing PIM-PIs. In addition, as the van der Waals volume of halogen atoms increases, the gas permeability of halogen-containing PIM-PIs exhibits an increasing trend. Specifically, compared with BFPI, the CO2 permeability of BCPI and BBPI is increased by 48 % and 100 %, respectively. Our findings may elucidate the structure-property relationship of microporous polymer membranes and provide a brand-new insight to design an advanced high-performance membrane.

Novel ibuprofen prodrug: A possible promising agent for the management of complications of Alzheimer’s disease

BackgroundAlzheimer’s disease (AD) is a severe, varied, and complex brain condition that gradually impairs memory and cognitive function. Epidemiological studies have shown that patients who have a history of long-term NSAID use have a decreased risk of developing AD. The objective of this study is to conduct the structural analysis of a novel ibuprofen prodrug and test its anti-Alzheimer’s properties. MethodsComputational and docking studies were conducted using AMBER 18 package. The in-vivo studies were performed using aluminum chloride-induced experimental AD in rats. Adult Wistar rats of either sex were used and treated with aluminum chloride (32.5 mg/kg, p.o) and ibuprofen prodrug (50 mg/kg, p.o) daily for 30 days. The hole-board test and elevated plus maze were conducted on 10th, 20th and 30th day. Further, on 31st day, animals were euthanized and the brain tissue was used for histopathology. The results obtained were subjected to statistical analysis by one-way ANOVA and Dunnet’s test, p < 0.05 was considered to indicate the significance. ResultsThe structural configuration of the novel compound indicated the presence of several structures such as aliphatic, aromatic, and asymmetry in the compound. The geometrical analysis indicated that the ibuprofen conjugate has dreiding energy of 51.22 kcal/mol with a van der waals radius of 62.56 A. The Huckel analysis confirmed the presence of aromatic rings in the compound. The molecular docking studies suggested affinity towards beta-secretase and acetylcholinesterase, besides indicating that the compound has ideal characteristics for the oral route (Log P = 2.33), cellular absorption (TPSA = 95.50), and oral bioavailability (number of rotatable bonds = 10). The toxicity profile indicated devoid of major systemic toxicity with mild possibility of cytotoxicity. The in-vivo analysis showed that the Ibu-prodrug significantly (P < 0.001) reversed the changes induced by aluminum chloride and restored histomorphological features in brain tissue. ConclusionThe findings suggested that the ibuprofen conjugate might possess the potential to manage the complications of AD. The action appears to be mediated through inhibition of beta-secretase and acetylcholinesterase activities. More studies might aid in identifying a specific therapeutic intervention that is still lacking in the treatment of AD.

Atomic scale volume and grain boundary diffusion elucidated by in situ STEM

Diffusion is one of the most important phenomena studied in science ranging from physics to biology and, in abstract form, even in social sciences. In the field of materials science, diffusion in crystalline solids is of particular interest as it plays a pivotal role in materials synthesis, processing and applications. While this subject has been studied extensively for a long time there are still some fundamental knowledge gaps to be filled. In particular, atomic scale observations of thermally stimulated volume diffusion and its mechanisms are still lacking. In addition, the mechanisms and kinetics of diffusion along defects such as grain boundaries are not yet fully understood. In this work we show volume diffusion processes of tungsten atoms in a metal matrix on the atomic scale. Using in situ high resolution scanning transmission electron microscopy we are able to follow the random movement of single atoms within a lattice at elevated temperatures. The direct observation allows us to confirm random walk processes, quantify diffusion kinetics and distinctly separate diffusion in the volume from diffusion along defects. This work solidifies and refines our knowledge of the broadly essential mechanism of volume diffusion.

IR, Raman spectroscopic, DFT, AIM and NCI characterization of O-H‧‧‧O/π‧‧‧π bonds in dimer and trimer species as computed from MD simulations in water for Protocatechuic acid

In the present work we report a study of the O-H‧‧‧O dimer, bifurcated dimer and O-H‧‧‧O/π‧‧‧π bonded trimer species as determined by Molecular Dynamics simulations for Protocatechuic acid. Multiple O-H‧‧‧O bond interactions are correlated to the unsymmetrical broad band structure observed in the experimental IR absorption spectrum near 3400 cm−1. To gain an understanding of the O-H‧‧‧O/π‧‧‧π bond interactions and its resultant structures referred above, we carried out MD simulations using ten monomer species in water solvent of 1000 molecules for 1 ns. We have identified different O-H‧‧‧O bonds between hydroxyl-hydroxyl, carboxyl-hydroxyl and carboxyl-carboxyl groups in the dimer and bifurcated dimer species, whereas in the trimer, there are O-H‧‧‧O bonds and π‧‧‧π bonds in ring-to-ring interactions. Computed radial distribution functions confirm that (i) the O-H‧‧‧O/π‧‧‧π bonds exist in all the dimer/trimer species; (ii) the donor-acceptor bond lengths in O-H‧‧‧O bonds are less than the sum of van der Waals radii of the H and O atoms. Lifetimes of the O-H‧‧‧O bonds at 5.0 to 13.5 ps correspond to the association/dissociation of those bonds. Stabilization energies for both intra- and inter-molecular O-H‧‧‧O bonds in the dimer and trimer lie in the range 0.93 – 11.20 kcal/mol. Stabilization energies of the six π‧‧‧π bonded trimer species lie in the range 0.13 – 0.44 kcal/mol. Geometry, vibrational modes and other electronic properties for the most stable dimer computed at B3LYP/6-311++G (d, p) level has been shown to be a satisfactory model.

Cobalt-59 NMR relaxation times of symmetric tris(γ-substituted-acetylacetonato)cobalt(III) complexes in benzene

Cobalt-59 NMR relaxation times, T1(59Co), and chemical shifts, δ(59Co), of symmetric tris(γ-substituted-acetylacetonato)cobalt(III) complexes, [Co(acac-X)3], which have chloride, bromide, nitro, and phenyl groups at the methine carbon atoms in the chelate ligands, have been measured in benzene at four temperatures between 284 and 319 K. In view of the viscosity dependence of 1/T1(59Co), the 59Co relaxation is caused by the reorientation of the static electric field gradient at the nucleus in every complex. Assuming that the rotational volume is replaced by the van der Waals volume, the nuclear quadrupolar coupling products, {(1 + ηq2/3)(eQq/h)2}1/2, were obtained for the series of [Co(acac-X)3] complexes in benzene. The negative correlation between {(1 + ηq2/3)(eQq/h)2}1/2 and δ(59Co) was observed for the four complexes [Co(acac)3], [Co(acac-Cl)3], [Co(acac-Br)3], and [Co(acac-NO2)3] except for [Co(acac-Ph)3]. This discrepancy strongly suggests that the rotational volume of the propeller-like [Co(acac-Ph)3] complex with the protruding phenyl groups cannot be simply treated as the van der Waals volume, different from the other almost spherical complexes. Actually, the estimation of the rotational volumes from the distances between the central cobalt and g-substituents gave much better correlation between {(1 + ηq2/3)(eQq/h)2}1/2 and δ(59Co) for all the complexes including [Co(acac-Ph)3].

Computational Insight into the Nature and Strength of the π-Hole Type Chalcogen∙∙∙Chalcogen Interactions in the XO2∙∙∙CH3YCH3 Complexes (X = S, Se, Te; Y = O, S, Se, Te).

In recent years, the non-covalent interactions between chalcogen centers have aroused substantial research interest because of their potential applications in organocatalysis, materials science, drug design, biological systems, crystal engineering, and molecular recognition. However, studies on π-hole-type chalcogen∙∙∙chalcogen interactions are scarcely reported in the literature. Herein, the π-hole-type intermolecular chalcogen∙∙∙chalcogen interactions in the model complexes formed between XO2 (X = S, Se, Te) and CH3YCH3 (Y = O, S, Se, Te) were systematically studied by using quantum chemical computations. The model complexes are stabilized via one primary X∙∙∙Y chalcogen bond (ChB) and the secondary C-H∙∙∙O hydrogen bonds. The binding energies of the studied complexes are in the range of -21.6~-60.4 kJ/mol. The X∙∙∙Y distances are significantly smaller than the sum of the van der Waals radii of the corresponding two atoms. The X∙∙∙Y ChBs in all the studied complexes except for the SO2∙∙∙CH3OCH3 complex are strong in strength and display a partial covalent character revealed by conducting the quantum theory of atoms in molecules (QTAIM), a non-covalent interaction plot (NCIplot), and natural bond orbital (NBO) analyses. The symmetry-adapted perturbation theory (SAPT) analysis discloses that the X∙∙∙Y ChBs are primarily dominated by the electrostatic component.

Computational approach to identify structural and elastic relationship in metastable crystalline and amorphous alloy thin films: Mo1-xNix and Mo1-xSix case studies

Previously well-established experimental trends of ground-state properties of crystalline and amorphous Mo1-xSix and Mo1-xNix alloys with 0 ≤ x ≤ 1 are predicted by first-principles calculations and inter-relationship with sound velocities and elastic properties are identified. The free energy of mixing, calculated at 300 K provides accurate values of the critical Si and Ni concentrations leading to the crystalline-to-amorphous transition. Specifically, a transition from BCC to amorphous state is predicted for xSi ~ 0.14 and xNi ~ 0.32, while FCC to amorphous transition is observed for xNi ~ 0.77. These structural transitions are accompanied by modifications of the out-of-plane longitudinal and shear elastic constants. In the crystalline region, a pronounced softening of elastic moduli is predicted for both solid solution alloys. While for amorphous Mo-Ni, the elastic constants do not undergo significant changes, for amorphous Mo-Si, they exhibit two distinct behaviors depending on the electronic properties and bonding character. For 0.2 ≤ xSi ≤ 0.7, the metallic character of the amorphous alloys is maintained and the elastic properties are remarkably stable. For xSi > 0.7, a progressive increase in the atomic volume is observed and the amorphous alloys acquire a covalent character and a reduced coordination number. Surprisingly, during this transition, both the longitudinal and shear acoustic velocities continuously increase, despite a progressive softening of the elastic stiffness constants. These calculations provide deep insight at the atomic-scale and reproduce satisfactorily the earlier experimental works of magnetron co-sputtered Mo-Si films, while some disagreement on elastic properties remain for more energetic ion beam sputtered Mo-Ni films, likely partially attributed to point-defects.

2-Amino Thiazole Derivatives as Prospective Aurora Kinase Inhibitors against Breast Cancer: QSAR, ADMET Prediction, Molecular Docking, and Molecular Dynamic Simulation Studies.

The aurora kinase is a key enzyme that is implicated in tumor growth. Research revealed that small molecules that target aurora kinase have beneficial effects as anticancer agents. In the present study, in order to identify potential antibreast cancer agents with aurora kinase inhibitory activity, we employed QSARINS software to perform the quantitative structure-activity relationship (QSAR). The statistical values resulted from the study include R2 = 0.8902, CCCtr = 0.7580, Q2 LOO = 0.7875, Q2LMO = 0.7624, CCCcv = 0.7535, R2ext = 0.8735, and CCCext = 0.8783. Among the four generated models, the two best models encompass five important variables, including PSA, EstateVSA5, MoRSEP3, MATSp5, and RDFC24. The parameters including the atomic volume, atomic charges, and Sanderson's electronegativity played an important role in designing newer lead compounds. Based on the above data, we have designed six series of compounds including 1a-e, 2a-e, 3a-e, 4a-e, 5a-e, and 6a-e. All these compounds were subjected to molecular docking studies by using AutoDock v4.2.6 against the aurora kinase protein (1MQ4). Among the above 30 compounds, the 2-amino thiazole derivatives 1a, 2a, 3e, 4d, 5d, and 6d have excellent binding interactions with the active site of 1MQ4. Compound 1a had the highest docking score (-9.67) and hence was additionally subjected to molecular dynamic simulation investigations for 100 ns. The stable binding of compound 1a with 1MQ4 was verified by RMSD, RMSF, RoG, H-bond, molecular mechanics-generalized Born surface area (MM-GBSA), free binding energy calculations, and solvent-accessible surface area (SASA) analyses. Furthermore, newly designed compound 1a exhibited excellent ADMET properties. Based on the above findings, we propose that the designed compound 1a may be utilized as the best theoretical lead for future experimental research of selective inhibition of aurora kinase, therefore assisting in the creation of new antibreast cancer drugs.

Solute-strengthening in metal alloys with short-range order

Recent surging interest in strengthening of High Entropy Alloys (HEAs) with possible chemical ordering motivates the development of new theory. Here, an existing theory for random alloys that accounts for solute-dislocation and solute–solute interactions is extended to include strengthening due to short-range order (SRO). Closed form expressions are presented for the yield strength and energy barrier of dislocation motion in alloys with SRO based on inputs of atomic misfit volumes, average lattice and elastic constants, the SRO parameters, and effective pair interactions between solutes. The theory shows both the long-established athermal strengthening effect of SRO as well as a notable effect of SRO on the misfit volume strengthening, which can increase or decrease strength. The generalized solute-strengthening theory is the most comprehensive to date that is applicable to macroscopically homogeneous single-phase alloys using inputs that can be measured, computed, or estimated.

Fitting high-resolution electron density maps from atomic models to solution scattering data

Solution scattering techniques, such as small- and wide-angle X-ray scattering (SWAXS), provide valuable insights into the structure and dynamics of biological macromolecules in solution. In this study, we present an approach to accurately predict solution X-ray scattering profiles at wide angles from atomic models by generating high-resolution electron density maps. Our method accounts for the excluded volume of bulk solvent by calculating unique adjusted atomic volumes directly from the atomic coordinates. This approach eliminates the need for one of the free fitting parameters commonly used in existing algorithms, resulting in improved accuracy of the calculated SWAXS profile. An implicit model of the hydration shell is generated that uses the form factor of water. Two parameters, namely the bulk solvent density and the mean hydration shell contrast, are adjusted to best fit the data. Results using eight publicly available SWAXS profiles show high-quality fits to the data. In each case, the optimized parameter values show small adjustments demonstrating that the default values are close to the true solution. Disabling parameter optimization produces significantly more accurate predicted scattering profiles compared to the leading software. The algorithm is computationally efficient, comparable to the leading software and up to 10 times faster for large molecules. The algorithm is encoded in a command line script called denss.pdb2mrc.py and is available open source as part of the DENSS v1.7.0 software package. In addition to improving the ability to compare atomic models to experimental SWAXS data, these developments pave the way for increasing the accuracy of modeling algorithms using SWAXS data and decreasing the risk of overfitting.

Heterogeneous N-heterocyclic carbenes supported single-atom catalysts for nitrogen fixation: A combined density functional theory and machine learning study

Electrocatalytic nitrogen reduction reaction (NRR) has emerged as a sustainable and eco-friendly alternative for ammonia production at ambient conditions. Exploring highly efficient and selective electrocatalysts for NRR continues to gain significant attention, but remains a challenge. In this work, we conducted a series of single-atom catalysts (SACs) by embedding 29 kinds of transition metal (TM) atoms on the two-dimensional heterogeneous N-heterocyclic carbene, and systematically investigated their catalytic performance for NRR using density functional theory, high-throughput screening, and machine learning. Two promising candidates (TM = Mn and Ta) with high catalytic activity and selectivity were identified, with limiting potentials of - 0.51 and - 0.53 V, respectively. Moreover, considering solvation effects, the limiting potential for Mn was further reduced to -0.43 V. Machinelearning(ML)analysis revealedthat the adsorption energy of N2 emerged as an efficient descriptor for NRR activity, and transition metal atomic Mendeleev number (Nm), the molar volume of TM atoms (Vm) and the 1st ionization energy of TM atoms (Im) were intrinsic to the difference in NRR performance of these SACs. Our findings demonstrate a novel class of efficient SACs based on heterogeneous N-heterocyclic carbene, offering valuable insights for further design of NRR electrocatalysts with exceptional catalytic performance.

Design of High-Performance Organic Nonlinear Optical and Terahertz Crystals by Controlling the van der Waals Volume.

In the development of new organic crystals for nonlinear optical and terahertz (THz) applications, it is very challenging to achieve the essentially required non-centrosymmetric molecular arrangement. Moreover, the resulting crystal structure is mostly unpredictable due to highly dipolar molecular components with complex functional substituents. In this work, new organic salt crystals with top-level macroscopic optical nonlinearity by controlling the van der Waals volume (VvdW ), rather than by trial and error, are logically designed. When the VvdW of molecular ionic components varies, the corresponding crystal symmetry shows an observable trend: change from centrosymmetric to non-centrosymmetric and back to centrosymmetric. All non-centrosymmetric crystals exhibit an isomorphic P1 crystal structure with an excellent macroscopic second-order nonlinear optical response. Apart from the top-level macroscopic optical nonlinearity, new organic crystals introducing highly electronegative fluorinated substituents with strong secondary bonding ability show excellent performance in efficient and broadband THz wave generation, high crystal density, high thermal stability, and good bulk crystal growth ability.

Computational workflow for steric assessment using the electric field-derived size

Molecular structure plays an important role in the selectivity and performance of catalysts. Understanding the impact of structural differences on catalyst performance via quantitative structure-selectivity relationships is key to developing high-performing catalytic systems. There are several methods that have been introduced to quantify steric contributions, including Tolman cone angles, Charton parameters, and A-values. While these have shown promise in predicting selectivity, they access similar, general steric contributions and are largely empirically derived. Alternatively, Sterimol parameters offer a specific multi-directional measure of steric bulk in the form of three vectors in units of distance. Recently, these parameters revealed strong correlations between structure and selectivity in asymmetric catalysis. Yet, despite their demonstrated performance, Sterimol parameters are commonly derived using van der Waals radii, which approximate molecular size using hard-spheres. This method may not accurately describe highly polarized systems. Recently, a new chemical system size metric based on the electric-field of a molecule was developed, which accesses the occupied space of a molecule. Here, we demonstrate that the electric field-derived Sterimol parameters reveal similar structure-selectivity relationships in asymmetric catalysis as conventional Sterimol parameters. Specifically, we present a computational workflow for calculating Sterimol parameters based on the size of a molecule’s electric field, and validate our method using several asymmetric catalysis reactions.