Accurate and simple analytic representation of the electron-gas correlation energy

Ni3Fe/NiFe2O4 heterojunction engineering and vanadium promoter synergetically accelerating urea degradation

Urea oxidation reaction (UOR) is significant in reducing hydrogen production energy consumption and treating urea wastewater, necessitating the development of efficient UOR electrocatalysts. Herein, we develop a vanadium (V)-doped Ni3Fe/NiFe2O4 heterojunction (V-Ni3Fe/NiFe2O4), wherein the combined effect of V doping and the heterojunction architecture improve the material's conductivity, facilitate electron transfer, and optimize the electronic structure of active sites. Consequently, the V-Ni3Fe/NiFe2O4 electrocatalyst requires a potential of only 1.48 V to achieve a current density of 100 mA·cm-2 and achieves ∼78 % urea degradation within 3 h. Density functional theory calculations reveal that V doping increases the density of states near the Fermi level of Ni3Fe/NiFe2O4, thereby enhancing the electron transfer capability. Moreover, the formation of the heterojunction structure improves urea adsorption and lowers the energy barrier for the UOR. This study offers valuable insights for the rational design of heterojunction-based UOR electrocatalysts.

Vibrational assignments, normal coordinates analysis, force constants, and DFT/MP2 computations of 5-Chloro-2,4,6-trifluoropyrimidine

The vibrational assignments of 5-Chloro-2,4,6-trifluoropyrimidine have been early investigated, however, the proposed fundamentals were not spanned to their appropriate species owing to neglecting the overall symmetry. Nevertheless, the lack of force constants (FCs) determination encourages us to reinvestigate the molecule. Aided by DFT (B3LYP, B3P86, B3PW91, ωBX97) and MP2 = full quantum chemical computations, we have provided a reliable vibrational analysis of all normal modes based on the C2v point group. Different methods of the currently used normal coordinate analysis were also validated. Our results are compared with available infrared and Raman spectral data, including estimated infrared intensities, Raman scattering activities, genuine FCs in internal coordinates, and potential energy distributions (PEDs). Using NCA in a well-defined internal coordinate that enables us to estimate FCs based on G.F. Wilson led to better fundamental interpretations than those obtained from atomic displacements in Cartesian coordinates, VEDA, and MOLVIB programs. The current investigation potentially offers corrected vibrational mode assignments, filling gaps in prior literature and aiding in accurately characterizing fluorinated pyrimidine derivatives.

Tailoring functionalized 2,3-diaza-1,3-butadienes for high-energy and insensitive applications

The heat of formation (HOF), detonation performance, electronic properties, thermal stability, impact energy and explosive power of a series of highly functionalized 2,3-diaza-1,3-butadienes were studied using density functional theory. HOF values of all the designed compounds were positive. Among the 100 compounds, more than 50 % exhibited a density equal to or greater than 1.9 g cm-3. There was close agreement in the calculated value of density, detonation performance and impact energy of traditional explosive RDX, HMX and CL-20 with the experimental value. The predicted values of detonation velocity and pressure indicated that about 45 compounds possessed values higher than that of 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX), among which 20 compounds had higher impact energy than HMX. Five compounds were identified as potential front-runners with superior detonation performance greater than CL-20, together with impact energy higher than HMX. Thus compounds with improved properties were designed by the adoption of strategies that involved the incorporation of diverse explosophores and nitrogen atoms in the ring and the framework. Our study proves that this work holds immense potential in the development of high-energetic density materials with promising properties.

Excited states of the uniform electron gas

The uniform electron gas (UEG) is a cornerstone of density-functional theory (DFT) and the foundation of the local-density approximation, one of the most successful approximations in DFT. In this work, we extend the concept of UEG by introducing excited-state UEGs, systems characterized by a gap at the Fermi surface created by the excitation of electrons near the Fermi level. We report closed-form expressions of the reduced kinetic and exchange energies of these excited-state UEGs as functions of the density and the gap. In addition, we derive the leading term of the correlation energy in the high-density limit. By incorporating an additional variable representing the degree of excitation into the UEG paradigm, the present work introduces a new framework for constructing local and semi-local state-specific functionals for excited states.

Dimensional reduction in Cs2AgBiBr6 enables long-term stable Perovskite-based gas sensing

Halide perovskite gas sensors have a low gas detection limit at room temperature, surpassing the performance of traditional metal oxide chemiresistors. However, they are prone to structural decomposition and performance loss due to the lack of coordination unsaturated surface metal ions and sensitivity to environmental factors such as water, oxygen, heat, and light. To address this issue, we present a general strategy: replacing the cation Cs+ in inorganic perovskite Cs2AgBiBr6 with long-chain alkylamines. This modification synthesizes perovskite sensor materials that effectively block moisture and exhibit excellent stability under real-working conditions. The chemiresistors show high sensitivity and stability to CO gas, with (BA)4AgBiBr8 detecting CO at a limit of 20 ppb, maintaining performance after 270 days of continuous exposure to ambient air. The exceptional performance of (BA)4AgBiBr8 is elucidated through density functional theory calculations combined with sum frequency generation spectroscopy, marking a significant breakthrough in halide perovskite-based gas sensing by surpassing the stability and sensitivity of traditional sensors.

Extending tetrahedral network similarity to carbon: A type-I carbon clathrate stabilized by boron

Clathrates are guest/host framework compounds composed of polyhedral cages, yet despite their prevalence among tetrahedral network formers, clathrates with a carbon host lattice remain unrealized synthetic targets. Here, we report a type-I carbon-based framework-a ubiquitous clathrate structure type found throughout compounds containing tetrahedral building blocks. Following a boron-stabilization scheme based on first-principles predictions in the Ca-B-C system at high pressure, type-I Ca8BxC46-x (x ≈ 9) was synthesized in the archetypal Pm[Formula: see text]n lattice with stability derived from substitutionally disordered boron atoms on hexagonal ring framework positions. The synthesized clathrate, which is recoverable to ambient conditions, expands topological network similarity across tetrahedral systems and opens possibilities for a broad family of diamond-like, carbon-based compounds with tunable properties based on the wide potential for guest/host-atom substitutions and framework versatility.

Rational design of mixed-valence cobalt-based nanowires via simultaneous vanadium and iron modulations for enhanced alkaline electrochemical water splitting

Strategic modulation of the electronic structure and surface chemistry of electrocatalysts is crucial for achieving highly efficient and cost-effective bifunctional catalysts for water splitting. This study demonstrated the strategic incorporation of redox-active elements (vanadium (V) and iron (Fe)) to optimize the catalytic interface of mixed-valence cobalt-based nanowires (Co5.47N and CoP), which enhanced their hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalytic activity. Experimental and theoretical analyses revealed that the dual-cation doping increased the surface area and optimized the electronic structure of the nanowires, which promoted rapid water dissociation, favoured hydrogen adsorption kinetics, and stabilized the oxygen intermediates. Consequently, the V,Fe-Co5.47N and V,Fe-CoP nanowire electrocatalysts achieved low overpotentials of 55/251 and 63/265 mV for HER/OER at 10 mA cm-2 in 1 M KOH electrolyte, respectively, outperforming their pristine and single-cation-doped counterparts. The alkaline overall water-splitting devices assembled based on these bifunctional catalysts required an overall voltage of only 1.64 V and 1.66 V at 100 mA cm-2 and also demonstrated excellent durability. This work provides valuable insights into enhancing transition metal-based catalysts through the incorporation of redox-active elements for efficient water splitting.

Unraveling the mechanisms of ketene generation and transformation in syngas-to-olefin conversion over ZnCrO x |SAPO-34 catalysts

Ketene was identified as an intermediate in syngas-to-olefin (STO) conversion catalyzed by metal oxide-zeolite composites, which sparked a hot debate regarding its formation mechanism and catalytic roles. Here, we employed large-scale atomic simulations using global neural network potentials to explore the STO reaction pathways and microkinetic simulations to couple the reaction kinetics in ZnCrO x |SAPO-34 composite sites. Our results demonstrate that the majority of ketene (86.1%) originates from the methanol carbonylation-to-ketene route via nearby zeolite acidic sites, where methanol is produced through conventional syngas-to-methanol conversion on the Zn3Cr3O8 (0001) surface, while the minority of ketene (13.9%) arises from a direct CHO*-CO* coupling pathway (CHO* + CO* + H* → CHOCO* + H* → CH2CO + O*) on Zn3Cr3O8. The presence of the ketene pathway significantly alters the catalytic performance in the zeolite, as methanol carbonylation to ketene is kinetically more efficient in competing with conventional methanol-to-olefins (MTO) conversion and thus predominantly drives the product to ethene. Based on our microkinetic simulation, it is the methanol carbonylation activity in the zeolite that dictates the performance of STO catalysts.

Structural Evolution and Chemical Bonding in Rare-Earth Encapsulated Magnesium Clusters: A CALYPSO-Guided DFT Study of La2Mgn and Lu2Mgn (N = 1-20)

The initial geometric configurations of gas-phase doped magnesium clusters incorporating rare-earth elements (La2Mgn and Lu2Mgn, n = 1-20) were systematically explored using the CALYPSO structure prediction software. Subsequent density functional theory (DFT) calculations were performed to conduct a comparative analysis of their structural evolution, stability, electronic properties, vibrational spectra, and chemical bonding characteristics. Key findings reveal that both La2Mgn and Lu2Mgn clusters adopt cage-like architectures for medium sizes (n ≥ 10), with rare-earth atoms encapsulated within the magnesium framework. Stability analyses identified La2Mg10, La2Mg15, Lu2Mg10, and Lu2Mg15 as potential ″magic-number″ clusters exhibiting enhanced relative stability. Electronic structure investigations through natural population analysis (NPA) demonstrate consistent electron transfer from Mg to rare-earth atoms, with lutetium exhibiting greater electron affinity than lanthanum. Notably, valence orbital distributions reveal distinct hybridization patterns between 5d/6s (Lu) and 5d/6s/4f (La) atomic orbitals. Theoretical infrared and Raman spectra predictions provide characteristic vibrational fingerprints to guide future experimental identification. Bonding critical point (BCP) analysis via atoms-in-molecules (AIM) theory further elucidates the nature of interatomic interactions in these heterometallic systems.

Overcoming Challenges in Density Functional Theory-Based Calculations of Hyperfine Coupling Constants for Heavy Heteroatom Radicals

This study assesses density functional theory (DFT) methods for their accuracy in calculating hyperfine coupling constants (HFCCs) of heavy heteroatom radicals with heteroatoms including Sb, Bi, In, Tl, and Sn. Given the essential role of electron paramagnetic resonance spectroscopy in characterization of these species, it is crucial that theoretical models can predict HFCCs accurately for heavy elements. This work presents a computational approach that addresses crucial factors: selection of basis set, hybrid exchange-correlation functional, higher Hartree-Fock (HF) exchange, and the Gaussian description of nuclear charge. The relativistic effects are introduced using one-component linear response theory with the second-order Douglas-Kroll-Hess formalism and the fully relativistic four-component Dirac-Kohn-Sham method. The findings show that, while one-component DFT is accurate for the 4th-row elements, the four-component method is more precise for the 5th-row radicals and the one-component approach fails for the 6th-row congeners. Increasing HF exchange significantly improves HFCC predictions. The developed framework for accurate HFCC calculations will enhance the understanding of electronic and magnetic properties of heavy element radicals and can be used by computational chemists and experimentalists alike.

Sensitivity of Projections of Backbone 13Cα/15N Chemical Shielding Along Covalent Bonds to Protein Secondary Structure-An Ab Initio Study

Statistical analysis of backbone 13Cα and 15N chemical shielding tensors (CST) computed using the DFT-GIAO method is presented for 40 alanine residues located centrally in three-residue segments extracted from α-helical and β-sheet regions of 12 proteins with high-resolution crystal structures. Our results show that the projections of 13Cα shielding along the three covalent bond directions, Cα-Cβ, Cα-Hα, and Cα-N, exhibit significantly higher sensitivity to secondary structure than the principal components. The increased sensitivity is due to the changes in the orientation of 13Cα CST in the molecular frame of the two secondary structures. Similarly, the projections of backbone amide 15N shielding along the covalent bonds N-H, N-Cα and along the normal direction to the peptide plane have a reasonably higher sensitivity to the secondary structure than the principal components. Unlike 13Cα nuclei, the orientation of amide 15N CST in the molecular frame is found to be invariant in the two secondary structures. The calculated amide 15N chemical shielding anisotropies (CSA) are larger in helix than in sheet structure, consistent with the experimental 15N chemical shift studies reported in the literature. Furthermore, two-dimensional correlation plots of backbone 13Cα and 15N CSA parameters show a clear distinction between the two major secondary structure elements.

Synergistic niobium and manganese co-doping into RuO2 nanocrystal enables PEM water splitting under high current

Low-cost ruthenium-based catalysts with high activity have emerged as promising alternatives to iridium-based counterparts for acidic oxygen evolution reaction (OER) in proton exchange membrane water electrolyzers (PEMWE), but the poor stability under high current density remains as a key challenge. Here, we utilize the synergistic complementary strategy of introducing earth-abundant Mn and Nb dopants in ruthenium dioxide (RuO2) for Nb0.1Mn0.1Ru0.8O2 nanoparticle electrocatalyst that exhibits a low overpotential of 209 mV at 10 mA cm-2 and good stability of > 400 h at 0.2 A cm-2 in 0.5 M H2SO4. Significantly, a PEMWE device fabricated with Nb0.1Mn0.1Ru0.8O2 anode can operate continuously at least for 1000 h at 0.5 A cm-2 with 59 μV h-1 decay rate. Operando Raman spectroscopy analysis, differential electrochemical mass spectroscopy measurements, X-ray absorption spectroscopy analysis and theoretical calculations indicate that OER reaction on Nb0.1Mn0.1Ru0.8O2 primarily follows the adsorbate evolution mechanism with much favorable energy barrier accompanied by a locally passivated lattice oxygen mechanism (AEM-LPLOM) and the co-existed Nb and Mn in RuO2 crystal lattice could not only stabilize the lattice oxygen, but also relieve the valence state fluctuation of Ru site to stabilize the catalyst during the reaction.

The Role of Cu3+ in the Oxygen Evolution Activity of Copper Oxides

Cu-based oxides and hydroxides represent an important class of materials from a catalytic and corrosion perspective. In this study, we investigate the formation of bulk and surface Cu3+ species that are stable under water oxidation catalysis in alkaline media. So far, no direct evidence existed for the presence of hydroxides (CuOOH) or oxides, which were primarily proposed by theory. This work directly places CuOOH in the oxygen evolution reaction (OER) Pourbaix stability region with a calculated free energy of -208.68 kJ/mol, necessitating a revision of known Cu-H2O phase diagrams. We also predict that the active sites of CuOOH for the OER are consistent with a bridge O* site between the two Cu3+ atoms with onset at ≥1.6 V vs the reversible hydrogen electrode (RHE), aligning with experimentally observed Cu2+/3+ oxidation waves in cyclic voltammetry of Fe-free and Fe-spiked copper in alkaline media. Trace amounts of Fe (2 μg/mL (ppm) to 5 μg/mL) in the solution measurably enhance the catalytic activity of the OER, likely due to the adsorption of Fe species that serve as the active sites . Importantly, modulation excitation X-ray absorption spectroscopy (ME-XAS) of a Cu thin-film electrode shows a distinct Cu3+ fingerprint under OER conditions at 1.8 V vs RHE. Additionally, in situ Raman spectroscopy of polycrystalline Cu in 0.1 mol/L (M) KOH revealed features consistent with those calculated for CuOOH in addition to CuO. Overall, this work provides direct evidence of bulk electrochemical Cu3+ species under OER conditions and expands our longstanding understanding of the oxidation mechanism and catalytic activity of copper.

Coupling Amorphization and Compositional Optimization of Ternary Metal Phosphides toward High-Performance Electrocatalytic Hydrogen Production

Amorphous materials, with abundant active sites and unique electronic configurations, have the potential to outperform their crystalline counterparts in high-performance catalysis for clean energy. However, their synthesis and compositional optimization remain underexplored due to the strict conditions required for their formation. Here, we report the synthesis of ternary platinum-nickel-phosphorus (PtNiP) amorphous nanoparticles (ANPs) within milliseconds by flash Joule heating, which features ultrafast cooling that enables the vitrification of metal precursors. Through compositional optimization, the Gibbs free energy of hydrogen adsorption for Pt4Ni4P1 ANPs is optimized at 0.02 eV, an almost ideal value, even surpassing that of the benchmark metallic platinum catalyst. As a result, the PtNiP ANPs exhibited superior activity in electrocatalytic hydrogen evolution in acid electrolyte (η10 ∼ 14 mV, Tafel slope ∼ 18 mV dec-1, and mass activity 5× higher than state-of-the-art Pt/C). Life-cycle assessment and technoeconomic analysis suggest that, compared to existing processes, our approach enables notable reductions in greenhouse gas emission, energy consumption, and production cost for practical electrolyzer catalyst manufacturing.

Effect of microhydration on the aromatic charge resonance interaction: the case of the pyrrole dimer cation

Charge resonance (CR) interactions between aromatic molecules are amongst the strongest intermolecular forces and responsible for many phenomena in chemistry and biology. Microhydration of an aromatic radical dimer cation allows investigation of the strong effects of stepwise solvation on the charge distribution and strength of the CR. We characterise herein the microhydration process of the pyrrole dimer cation (Py2+), a prototypical aromatic homodimer with a strong CR. The NH and OH stretch vibrations (νNH/OH) of mass-selected bare and colder Ar-tagged hydrated clusters of Py2+, Py2+(H2O)nArm (n ≤ 3, m ≤ 1), recorded by infrared photodissociation (IRPD) spectroscopy provide detailed insight into the preferred cluster growth and strengths of the various intermolecular interactions by comparison to dispersion-corrected density functional theory calculations. The analysis of systematic frequency shifts, structural parameters, binding energies, and charge distributions allows for a quantitative evaluation of the drastic effects of stepwise hydration on the strength and symmetry of the aromatic CR, the strengths of the various hydrogen bonds (H-bonds), and the competition between slightly noncooperative interior ion hydration and strongly cooperative formation of a H-bonded solvent network. The most stable Py2+H2O structure exhibits a strong NH⋯O ionic H-bond of H2O to the antiparallel stacked Py2+(a) core, thereby breaking the symmetry of the CR. Py2+(H2O)2 prefers a highly symmetric C2h structure with two equivalent NH⋯O H-bonds of Py2+(a) and an optimised CR. Starting from n = 3, clusters with a parallel configuration, Py2+(p), are more stable than those with Py2+(a), further highlighting the strong impact of (micro-)solvation on the structural motif of the aromatic CR. The spectral and computational data demonstrate a linear correlation of νNH of the free Py unit with its partial charge, illustrating that IR spectroscopy is a powerful tool for probing the charge distribution in aromatic CR cluster cations. Comparison of Py2+(H2O)n with neutral Py2(H2O)n and Py+(H2O)n reveals the impact of the magnitude of positive charge and the number of acidic proton donors on the structure of the microhydration shell and strength of the various competing intermolecular bonds.

Facile synthesis of cubic Ni1-xCrxnanoalloys and their composition-dependent electrocatalytic activity for the hydrogen evolution reaction

The viability of the electrolysis of water currently relies on expensive catalysts such as Pt that are far too impractical for industrial scale use. Thus, there is considerable interest in developing low-cost, earth-abundant nanomaterials and their alloys as a potential alternative to existing standard catalysts. To address this issue, a synergistic approach involving theory and experiment was carried out. The former, based on density functional theory, was conducted to guide the experiment in selecting the ideal dopant and optimal concentration by focusing on 3d, 4d, and 5d elements as dopants on Ni (001) surface. Subsequently, a series of Ni1-xCrx(x= 0.01-0.09) alloy nanocrystals (NCs) with size ranging from 8.3 ± 1.6-18.2 ± 3.2 nm were colloidally synthesized to experimentally investigate the hydrogen evolution reaction (HER) activity. A compositional dependent trend for electrocatalytic activity was observed from both approaches with Ni0.92Cr0.08NCs showed the lowest ΔGHvalue and the lowest overpotential (η-10) at -10 mA cm-2current density (j), suggesting the highest HER activity among all compositions studied. Among alloy NCs, the highest performing Ni0.92Cr0.08composition displayed a mixed Volmer-Heyrovsky HER mechanism, the lowest Tafel slope, and improved stability in alkaline solutions. This study provides critical insights into enhancing the performance of earth-abundant metals through doping-induced electronic structure variation, paving the way for the design of high-efficiency catalysts for water electrolysis.

Computational design of dopant-free hole transporting materials: achieving an optimal balance between water stability and charge transport

Hole transporting materials (HTMs) play a crucial role in the performance and stability of perovskite solar cells (PSCs). The interaction of HTMs with water significantly affects the overall stability and efficiency of these devices. Hydrophilic HTMs or those lacking adequate water resistance can absorb moisture, leading to degradation of both the HTM and the perovskite layer. In this study, we employed a proof-of-principle approach to investigate the effect of various chemical modifications on a promising HTM candidate, 8,11-bis(4-(N,N-bis(4-methoxyphenyl)amino)-1-phenyl)-dithieno[1,2-b:4,3-b]phenazine (TQ4). Using molecular dynamics simulations, we examined the collective behavior of chemically modified TQ4 molecules in the presence of water at different concentrations. To ensure that enhanced water resistance did not compromise the desirable electronic properties of the HTM, we analyzed both the individual and collective electronic structures of the HTM molecule and its molecular crystal. Additionally, we calculated the charge transport rate in different directions within the HTM crystal using Marcus theory. Our findings indicate that chemical modifications at the periphery of TQ4, particularly the symmetric addition of two F-chains, result in the optimal combination of electronic, crystal structure, and water-resistant properties. HOMO shape analysis reveals that the HOMO does not extend onto the added F-chains, reducing the maximum predicted hole mobility relative to TQ4 by an order of magnitude. Despite this, a hole mobility of 2.8 × 10-4 cm2 V-1 s-1 is successfully achieved for all designed HTMs, reflecting a compromise between stability and charge transport. This atomistic insight into the collective behavior of chemically modified HTMs and its effect on hole transport pathways paves the way for designing more effective HTMs for PSC applications.

Lima KA, da Silva DA, Mendonça FLL, Ribeiro Junior LA, Pereira Junior ML. Computational Design of 2D Nanoporous Graphene via Carbon-Bridged Lateral Heterojunctions in Armchair Graphene Nanoribbons

The interest in two-dimensional (2D) carbon allotropes arises from their ability to alter their properties based on the atomic topology employed, which can significantly affect their electronic properties and benefit advancements in new technologies. This work presents a new nanoporous graphene (NPG) allotrope obtained through lateral heterojunctions via pairs of trivalent sp2 carbon atoms of armchair graphene nanoribbons (AGNRs). These pairs were used as linkers between AGNRs to achieve this structure, forming connections that enhance the porous architecture. This novel planar and porous 2D carbon allotrope integrates some structural and electronic advantages of AGNRs into a 2D framework. Composed of 3-, 6-, and 12-membered carbon rings, the NPG was investigated using density functional theory (DFT) calculations and ab initio (AIMD) and classical molecular dynamics (CMD) simulations to explore its structural, electronic, and mechanical properties. Among the results presented, we show that the material demonstrates high dynamical and thermal stability at 1000 K. Furthermore, the NPG exhibits metallic and nonmagnetic behavior and is achieved by transitioning from the semiconducting nature of some AGNRs to a metallic 2D carbon system. The elastic properties reveal the material's distinct response to applied strain, with fractures occurring in the nanoribbon segment along the x-direction. However, fractures are observed in the C-C bonds involved in the heterojunction region in the y-direction. The calculated Young's modulus ranges from 394 to 690 GPa, which is lower but comparable to graphene. The formation energy of NPG decreases with increasing width of the AGNRs used to compose the 2D material, indicating enhanced stability for wider nanoribbons. These findings highlight the potential of NPG for applications in nanoelectronics and advanced new technologies.

Rational Design of Highly Stable and Active Single-Atom Modified S-MXene as Cathode Catalysts for Li-S Batteries

The practical application of Li-S batteries is hindered by the shuttle effect and sluggish sulfur conversion kinetics. To address these challenges, this work proposes an efficient strategy by introducing single atoms (SAs) into sulfur-functionalized MXenes (S-MXenes) catalysts and evaluate their potential in Li-S batteries through first-principles calculations. Using high-throughput screening of various SA-modified S-MXenes, this work identifies 73 promising candidates that exhibit exceptional thermodynamic and kinetic stability, along with the effective immobilization of polysulfides. Notably, the incorporation of Ni, Cu, or Zn as SAs into S-MXenes results in a significant Gibbs free energy barrier reduction by 51%-75%, outperforming graphene-based catalysts. This reduction arises from SA-induced surface electron density that influences the adsorption energies of intermediates and thereby disrupts the scaling relations between Li₂S₂ and other key intermediates. Further enhancement in catalytic performance is achieved through strain engineering by shifting the d-band center of metal atoms to higher energy levels, increasing the chemical affinity for intermediates. To elucidate the intrinsic adsorption properties of intermediates, this work develops a machine learning model with high accuracy (R2 = 0.88), which underscores the pivotal roles of SA electronegativity and local coordination environment in determining adsorption strength, offering valuable insights for the rational design of catalysts.

Electrochemical Performance of Layered Honeycomb Na2(Ni2-xCox)TeO6 (x = 0, 0.10, 0.25) Oxides as Sodium-Ion Battery Cathodes

To develop economically and environmentally viable sodium-based solid-state batteries, we investigated Na2(Ni2-xCox)TeO6 (x = 0, 0.10, 0.25). After synthesizing phase-pure compositions, we confirmed P63/mcm space group and P2 coordination through high-resolution synchrotron diffraction data, where Na+ occupies three different crystallographic positions in the unit cell: Na1, Na2, and Na3. With the incorporation of cobalt into the nickel lattice, an increase in the cell volume is seen. Bond parameters show that the average Ni-Ni distance increases as a result, but the local structure and coordination do not show marked differences. Our density functional theory calculations revealed that sodium at the Na1 site is energetically more favorable and that Co doping increased the lattice constants, supported by our X-ray diffraction data. Electrochemical measurements performed on half-cells versus sodium metal using CR2032-type coin cells revealed exceptionally high specific capacity matching the theoretical value and retained around 120 mAhg-1 at the smallest but optimum concentration of cobalt. The kinetics of storage mechanisms in these compositions reflect pseudo-capacitive behavior. Our results indicate that substitution pathways in the layered oxide family of Na2Ni2TeO6 offer the potential for the development of Na-based cathodes with enhanced cycling stability and ionic conductivity.

Elasticity and stability of GdAl2 under pressure and temperature investigated using DFT+AI

The cubic ferromagnetic Laves phase intermetallic compound [Formula: see text] is a promising candidate for aerospace, defense, and advanced engineering applications due to its thermal stability and reliable elastic properties under pressure. However, two key gaps persist: discrepancies between theoretical and experimental elastic constants, and a lack of systematic pressure-dependent investigations. This study addresses these gaps, highlighting [Formula: see text]'s exceptional thermal stability, with melting temperatures rising linearly under pressure, its near-isotropic compressive behavior, and mild anisotropy in shear and Young's moduli. Using density functional theory, elasticity theory, and AI-driven neural networks, we systematically analyzed the elasticity and stability of the system under pressure and temperature. A rigorous energy-based methodology resolves the first gap, setting a benchmark for cubic systems. To address the second gap, we analyzed mechanical stability up to 20 GPa via the Born stability criteria, finding consistent increases in elastic constants, bulk modulus, and Young's modulus under compression. Phonon dispersion and density of states analyses confirm dynamic stability and reveal that low-frequency acoustic modes dominated by Gd atoms drive elastic behavior, reflecting spin-dominated mechanics. Poisson's ratio shows mild anisotropy, while ductility assessments reaffirm the material's brittle nature, consistent with Laves phase intermetallics. By integrating advanced computational methods and AI predictions, this work resolves theoretical-experimental discrepancies, establishes a framework for spin-dominated systems, and positions [Formula: see text] as a benchmark for spin-lattice interactions and anisotropy in next-generation engineering under pressure.

Reusable Te-Doped Sn-P-I Catalysts With Anti-Healing P Vacancies and Stable I Sites for Efficient Black Phosphorus Growth

Black phosphorus (BP) holds significant potential for various applications, but its widespread use requires the development of efficient and cost-effective preparation methods. Sn-P-I clathrates are identified as potential catalysts for BP growth; however, the intact Sn-P-I structure leads to prolonged preparation times, rapid deactivation, and an unclear catalytic mechanism. In this study, a Te-doping strategy is proposed to simultaneously improve the activity and stability of Sn-P-I catalysts. Te doping induces the formation of Sn─Te bonds, creates intrinsic anti-healing phosphorus vacancies, while also mitigates iodine loss due to the lower electronegativity of Te compared to P. This doping changes the deactivation mechanism of the Sn-I-P from phosphorus saturation to iodine loss in the Te-doped Sn-I-P. To further improve catalyst reusability, an iodination treatment is introduced to reactivate the Te-Sn-P-I catalysts. The optimized Te-Sn-P-I catalyst reduced the reaction time for BP synthesis from 15 h to just 45 min, achieving a BP yield of 96.7%. The reactivation process restores 100% of the catalytic performance.

Defects repaired with oxygen-refilling activate the shallow states of carbon nitride for enhanced visible near-infrared photocatalytic activity

The efficient utilization of visible-near-infrared (vis-NIR) light of the solar spectrum is of great significance for the practical application of photocatalysis. However, developing photocatalysts with vis-NIR activity remains a great challenge. Here, we report a defect repair strategy to improve the vis-NIR photoactivity of recrystallized amorphous carbon nitride (O-ACN) by engineering the shallow electron trap states via oxygen-refilling defect sites. The obtained O-ACN suppresses the defect-induced deep states and non-radiative recombination, forming electron shallow trap states located at the Fermi level that enhance its electronic conductivity and charge transfer to improve vis-NIR photoactivity. The O-ACN produces H2O2 from H2O and O2 with an apparent quantum yield (AQY) of 5 % at 600 nm and 23 % at 420 nm, respectively. This work illustrates promising singular vis-NIR photocatalysts for solar-driven environmental remediation and clean chemical production.

Density functional benchmark for quadruple hydrogen bonds

Hydrogen bonding is an important non-covalent interaction that plays a major role in molecular self-organization and supramolecular structures. It can be described accurately with ab initio quantum chemical wave function methods, which become computationally expensive for large molecular assemblies. Density functional theory (DFT) offers a better balance between accuracy and computational cost, and can be routinely applied to large systems. A large number of density functional approximations (DFAs) has been developed, but their accuracy depend on the application, necessitating benchmark studies to guide their selection for use in applications. Some of us have recently determined highly accurate hydrogen bonding energies of 14 quadruply hydrogen-bonded dimers by extrapolating coupled-cluster energies to the complete basis set limit as well as extrapolating electron correlation contributions with a continued-fraction approach [U. Ahmed et al., Phys. Chem. Chem. Phys., 2024, 26, 24470-24476]. In this work, we study the reproduction of these bonding energies at the DFT level using 152 DFAs. The top ten density functional approximations are composed of eight variants of the Berkeley functionals both with and without dispersion corrections, and two Minnesota 2011 functionals augmented with a further dispersion correction. We find the B97M-V functional with the non-local correlation functional replaced by an empirical D3BJ dispersion correction to be the best DFA, while changes to the dispersion part in other Berkeley functionals lead to poorer performance in our study.

Electron deficient oxygen species in highly OER active iridium anodes characterized by X-ray absorption and emission spectroscopy

Water splitting is a promising technology for storing energy, yet it is challenged by the lack of stable anode materials that can overcome the sluggishness of the oxygen evolution reaction (OER). Iridium oxides are among the most active and stable OER catalysts, however how these materials achieve their performance remains under discussion. The activity of iridium based materials has been attributed to both high metal oxidation states and the appearance of O 2p holes. Herein we employ a combination of techniques-X-ray absorption at the Ir LII,III-edge, X-ray absorption and emission at the O K-edge, along with ab initio methods-to identify and characterize ligand holes present in highly OER-active X-ray amorphous oxides. We find, in agreement with the original proposition based on X-ray absorption measurement at the O K-edge, that O 2p holes are present in these materials and can be associated with the increased activity during OER.

Locating hydrogen in the Mg5Bi3Hx Zintl phase

The preparation of Zintl phases with pronounced spin-orbit coupling has received substantial scientific interest because of their distinctive electronic properties. In the context of superconductivity and topological phenomena related to band inversion, intermetallic compounds of bismuth have come into focus recently. While bismuth forms a rich variety of Zintl phases with the heavier alkaline-earth metals, there are significantly fewer magnesium compounds. Here we show that high-temperature high-pressure synthesis opens a convenient route for the preparation of Mg5Bi3Hx already at moderate conditions. The compound (space group Pnma, a = 11.5399(3) Å, b = 8.9503(2) Å and c = 7.8770(2) Å) adopts a Ca5Sb3F crystal structure. The minute amounts of hydrogen could only be detected by thermal decomposition of the compound in combination with mass spectroscopy of the gas phase. Direct space analysis of the chemical bonding allowed for allocating the hydrogen position at a partially occupied interstitial site and reveals strongly polar Mg-Bi and Mg-H bonds in accordance with the Zintl concept. Calculated band structures exhibit substantial electronic reorganization upon hydrogen insertion. The combination of advanced analytical tools in concert with modern quantum chemical techniques provides an efficient approach to allocate trace amounts of interstitial atoms stabilizing intermetallic phases.

Machine Learning-Driven Insights for Phase-Stable FA x Cs1-x Pb(I y Br1-y )3 Perovskites in Tandem Solar Cells

The inherent chemical tunability of perovskite materials has spurred extensive research into composition engineering within the perovskite community. However, identifying the optimal composition across a broad range of variations still remains a significant challenge. Conventional trial-and-error methods are prohibitively expensive and environmentally taxing for comprehensive screening. Here, we employed machine learning-accelerated atomic simulation to guide the design of stable perovskite solar cells absorbers. Our approach entailed training of a neural network (NN) potential using data generated from first-principles calculations, yielding a perovskite NN potential exhibiting high accuracy. Utilizing this NN potential, we constructed a phase diagram for FA x Cs1-x Pb(I y Br1-y )3 (where 0 ≤ x ≤ 1 and 0 ≤ y ≤ 1, FA denotes formamidinium cation). Integrating this with a band gap diagram, we successfully identified global optimal perovskite compositions for tandem applications with 1.7 and 1.8 eV band gaps. We have identified that all FA x Cs1-x Pb(I y Br1-y )3 with >1.8 eV band gaps are thermodynamically vulnerable to phase segregation and developed a strategy to stabilize thermodynamically unstable phases by suppressing phase segregation kinetics. Finally, theoretical predictions were confirmed by the corresponding experiments. Our results suggest that creating perovskites/Si tandem solar cells with 1.7 eV FA x Cs1-x Pb(I y Br1-y )3 encounters less severe challenges in addressing phase segregation issues than perovskites/perovskites tandem solar cells with 1.8 eV FA x Cs1-x Pb(I y Br1-y )3.

Optimization of Zinc and Aluminum Hydroxyquinolines for Applications as Semiconductors in Molecular Electronics

This work explores the dispersed heterojunction of tris-(8-hydroxyquinoline) aluminum (AlQ3) and 8-hydroxyquinoline zinc (ZnQ2) with tetracyanoquinodimethane (TCNQ) and 2,6-diaminoanthraquinone (DAAq). Thin films of these organic semiconductors were deposited and analyzed, with their structures calculated with the B3PW91/6-31G** method. The optimized structure for AlQ3-TCNQ, AlQ3-DAAq, is achieved by means of three hydrogen bonds, whereas for ZnQ2-DAAq, two hydrogen interactions are predicted. These structures were recalculated including the GD3 dispersion term. A stable ordering was also achieved for AlQ3-TCNQ-GD3, AlQ3-DAAq-GD3, and ZnQ2-DAAq-GD3 with four and two hydrogen contacts for the former and the two latter, respectively. Infrared (IR) and UV-visible spectroscopy confirmed these theoretical predictions, in addition to obtaining the optical band gap for the films. The optical band gap values ranged between 1.62 and 2.97 eV (theoretical) and between 2.46 and 2.87 eV (experimental). Additional optical parameters and electrical behavior were obtained, which indicates the potential of the films to be used as organic semiconductors. All three films showed transmittance above 76%, which also broadens the range of applications in electrodes, transparent transistors, or photovoltaic cells. Devices fabricated using these materials displayed ohmic electrical behavior, with peak current values between 2 × 10-3 and 6 × 10-3 A.

Fast Screening Suitable Doping Transition Metals to Na3V2(PO4)2F3 for Sodium-Ion Batteries with High Energy Density in Wide-Temperature Range

Screening the suitable doping elements for Na3V2(PO4)2F3 (NVPF) through the traditional trial-and-error method to enhance its intrinsic electronic conductivity and electrochemical performance is a time-exhausted task. Here, a new strategy of theoretical prediction-assisted chemical synthesis is proposed to fast filter the suitable doping elements to NVPF by first calculating the band gaps of various transition metals doped NVPF and then verifying by the experimental results. Single crystal NVPF-M (Na3V1.85M0.15(PO4)2F3, M = Ru, Fe, Ni, Ti, and Cd, etc.) materials are synthesized to compare their electrochemical performances. Excellent cycling performance (2000 cycles with high Coulombic efficiencies), remarkable rate capacity (20 C), and wide-temperature range (-30-60 °C) application capability are witnessed in the NVPF-Ru/Fe cathodes in both half and full cells. In situ X-ray diffraction patterns have confirmed that they followed the consisting of multi-phase reactions (Na3 ↔ Na2.4 ↔ Na2.2 ↔ Na1) and a solid-solution reaction (Na1.8 ↔ Na1.3) with small changes of lattice volume and strains. Compromising the cost and performance, the NVPF-Fe cathode is regarded as the optimized cathode for sodium-ion batteries with a high energy density and wide temperature application features.

Surface Reconstruction of Amorphous Ni─Co─S─O Material with a Functional Gradient Layer for Highly Efficient and Stable Alkaline Hydrogen Evolution

Alkaline water electrolysis holds potential for large-scale, high-purity hydrogen production. However, the slow kinetics of water dissociation and challenging conditions in alkaline environments complicate the search for an electrocatalyst with both high activity and durability. In this study, a highly active and stable amorphous electrocatalyst is introduced, 3Ni─Co─S─O, developed via a straightforward electrodeposition method for alkaline hydrogen evolution reaction (HER). Notably, the surface of the 3Ni─Co─S─O catalyst undergoes a compositional reconstruction during alkaline HER, yet maintains its amorphous structure. This reconstruction spans roughly 6 µm, leading to a gradual decrease in Ni and S content and a corresponding increase in O concentration toward the surface, thereby forming a stable, gradient active layer. Benefitting from this layer and its amorphous nature, the 3Ni─Co─S─O catalyst demonstrates superior alkaline HER activity-requiring only 170 mV to achieve an industrial HER current density of 1000 mA cm-2. It also showcases remarkable stability, with a mere 15 mV increase in overpotential during continuous HER at 300 mA cm-2 for 24 h, outperforming the commercial Pt/C catalyst. The research provides a novel approach to designing high-performance amorphous alkaline HER electrocatalysts cost-effectively and contributes insights for understanding and developing advanced amorphous catalysts across various applications.

Data-driven discovery of Pt single atom embedded germanosilicate MFI zeolite catalysts for propane dehydrogenation

Zeolite-confined metal is an important class of heterogeneous catalysts, demonstrating exceptional catalytic performance in many reactions, but the identification of a stable metal-zeolite combination with a simple synthetic method remains a top challenge. Here artificial intelligence methods, particularly global neural network potential based large-scale atomic simulation, are utilized to design Pt-containing zeolite frameworks for propane-to-propene conversion. We show that out of the zeolite database (>220 structure framework) and more than 100,000 Pt/Ge differently distributed configurations, there are only three Ge-containing zeolites, germanosilicate (MFI, IWW and SAO) that are predicted to be capable of stabilizing Pt single atom embedded in zeolite skeleton and at the meantime allowing propane fast diffusion. Among, the Pt1@Ge-MFI catalyst is successfully synthesized via a simple one-pot synthesis without a lengthy post-treatment procedure, and characterized by high-resolution experimental techniques. We demonstrate that the catalyst features an in-situ formed [GePtO3H2] active site under the reductive reaction condition that can achieve long-term (>750 h) high activity and selectivity (98%) for propane dehydrogenation. Our simple catalyst synthesis holds promise for scale-up industrial applications that can now be rooted in first principles via data-driven catalyst design.

Magnons from time-dependent density-functional perturbation theory and nonempirical Hubbard functionals

Spin excitations play a fundamental role in understanding magnetic properties of materials, and have significant technological implications for magnonic devices. However, accurately modeling these in transition-metal and rare-earth compounds remains a formidable challenge. Here, we present a fully first-principles approach for calculating spin-wave spectra based on time-dependent (TD) density-functional perturbation theory (DFPT), using nonempirical Hubbard functionals. This approach is implemented in a general noncollinear formulation, enabling the study of magnons in both collinear and noncollinear magnetic systems. Unlike methods that rely on empirical Hubbard U parameters to describe the ground state, and Heisenberg Hamiltonians for describing magnetic excitations, the methodology developed here probes directly the dynamical spin susceptibility (efficiently evaluated with TDDFPT throught the Liouville-Lanczos approach), and treats the linear variation of the Hubbard augmentation (in itself calculated non-empirically) in full at a self-consistent level. Furthermore, the method satisfies the Goldstone condition without requiring empirical rescaling of the exchange-correlation kernel or explicit enforcement of sum rules, in contrast to existing state-of-the-art techniques. We benchmark the novel computational scheme on prototypical transition-metal monoxides NiO and MnO, showing remarkable agreement with experiments and highlighting the fundamental role of these newly implemented Hubbard corrections. The method holds great promise for describing collective spin excitations in complex materials containing localized electronic states.

An active learning force field for the thermal transport properties of organometallic complex crystals

The accurate prediction of lattice thermal conductivity in organometallic thermoelectric materials is crucial for advancing energy conversion technologies. Methods based on molecular dynamics simulations can solve this problem well, but require force fields with sufficiently high accuracy. Due to the complexity of chemical bonding in organometallic complex materials, the development of force fields with high predictivity has been a long standing challenge, particularly when thermal transport is concerned which requires even greater accuracy. In recent years, the rapid advancement of machine learning force fields has offered substantial potential for addressing these issues. However, there remain challenges for materials with large organometallic complexes in one unit cell and both inter- and intra-molecular interactions. In this work, we employ an active learning approach combined with deep neural networks to develop a force field taking copper phthalocyanine as an example. The model utilizes a local environment descriptor for representation without explicitly characterizing the metal-organic coordination. The nonlinear mapping capabilities of deep neural networks enable the model to effectively capture higher-order many-body interactions. Furthermore, we utilized the Green-Kubo method to calculate the thermal conductivity of copper phthalocyanine, revealing a value of 0.49 W m-1 K-1 at 300 K, consistent with experimental findings (0.39 W m-1 K-1). This result significantly surpasses previous work with classical force fields. This work represents a significant advancement in demonstrating that machine-learning force fields can effectively characterize interactions in metal-organic complex systems and can significantly advance the development and discovery of organometallic thermoelectric materials.

Removal of ochratoxin A from wine by adsorption-photocatalytic synergy of tubular TiO2/SiO2/g-C3N4: Mechanistic insights and degradation pathways

Consumption of contaminated wines is a significant source of ochratoxin A (OTA) intake in humans, yet existing techniques for OTA removal are inadequate. This study constructs a TiO2/SiO2/g-C3N4 catalyst (TiSiMs-TCN) with a tubular structure, capable of efficiently removing OTA from both simulated and real wines under visible light irradiation. The results of experiments, characterizations, and theoretical calculations demonstrate that the incorporation of silica enhances the adsorption capacity for OTA, and the tubular structure improves the catalyst's photoelectric properties. The internal electric field between TiSiMs and TCN facilitates electron transfer and the generation of active species, rapidly degrading the adsorbed OTA and promoting the regeneration of active sites, thus maintaining continuous adsorption-photocatalysis synergy. The OTA degradation pathway was analyzed using the Fukui index, electrostatic potential distribution, and intermediate product identification. Toxicological experiments confirm that TiSiMs-TCN is a safe and stable material capable of effectively detoxifying OTA contamination.

Study of the Microstructure, Physical and Mechanical Properties of Zirconium Disilicide Ceramics: Synthesis, Experimental Characterization and Theoretical Calculations

Zirconium disilicide (ZrSi2) is often used in high-temperature applications due to its excellent mechanical properties and thermal stability. This study aims to investigate the microstructure and physical and mechanical properties of ZrSi2 ceramics prepared under high-pressure and high-temperature (HPHT) sintering conditions. The research results show that the density, Vickers hardness, and fracture toughness of the ZrSi2 ceramic sample reach 4.7 g/cm3, 10.547 GPa, and 6.905 MPa·m1/2, respectively. It is worth noting that the ZrSi2 ceramic sample exhibits excellent oxidation resistance and its oxidation starting temperature is 1463 °C. The experimentally measured thermal diffusion coefficient of the ZrSi2 ceramic sample is 2.815 mm2/s, and the specific heat capacity is 0.48 J/g·K, from which the thermal conductivity is calculated to be 6.354 W/m·K. The first-principles calculation results show that the crystal structure of ZrSi2 has good dynamic stability, and the silicon atoms and zirconium atoms are connected by strong covalent bonds. At the same time, the ZrSi2 ceramic sample obtained in this experiment has a uniform grain size distribution, a high dislocation density, and a strong texture. The results of this study are crucial for the preparation and application of ZrSi2 ceramics.

The electron localization function and the chemical interpretation of Fermi orbital descriptors in Fermi-Löwdin self-interaction correction calculations

A set of Fermi orbital descriptors (FODs), representing "semi-classical" electronic positions, is a crucial ingredient in the Fermi-Löwdin orbital self-interaction correction (FLOSIC) method. The FODs are utilized to generate Fermi orbitals, which, in turn, are symmetrically orthogonalized to give the Fermi-Löwdin orbitals employed in FLOSIC calculations. It has been argued, based on empirical evidence, that FODs carry chemical bonding information and that FOD arrangements are reminiscent of electron distributions predicted by Lewis or Linnett theory. Here, we show that there is a formal connection between FODs and critical points of the electron localization function (ELF) and illustrate this fact for several cases where fully relaxed FODs from FLOSIC calculations closely resemble the structure of critical points (CPs). We also propose a new localization function, the SIC-ELF, based on the local mobility of the Fermi orbitals. In certain instances involving double and triple bonds, FLOSIC FODs offer a more precise interpretation of the chemical bonding structure suggested by Lewis theory than ELF or SIC-ELF. We suggest that the connection between FODs and CPs can be exploited to obtain initial FOD configurations for FLOSIC calculations.

Giant thermally induced band-gap renormalization in anharmonic silver chalcohalide antiperovskites

Silver chalcohalide antiperovskites (CAP), Ag3XY (X = S, Se; Y = Br, I), are a family of highly anharmonic inorganic compounds with great potential for energy applications. However, a substantial and unresolved discrepancy exists between the optoelectronic properties predicted by theoretical first-principles methods and those measured experimentally at room temperature, hindering the fundamental understanding and rational engineering of CAP. In this work, we employ density functional theory, tight-binding calculations, and anharmonic Fröhlich theory to investigate the optoelectronic properties of CAP at finite temperatures. Near room temperature, we observe a giant band-gap (E g) reduction of approximately 20-60% relative to the value calculated at T = 0 K, bringing the estimated E g into excellent agreement with experimental measurements. This relative T-induced band-gap renormalization is roughly twice the largest value previously reported in the literature for similar temperature ranges. Low-energy optical polar phonon modes, which break inversion symmetry and enhance the overlap between silver and chalcogen s electronic orbitals in the conduction band, are identified as the primary drivers of this significant E g reduction. Furthermore, when temperature effects are considered, the optical absorption coefficient of CAP increases by nearly an order of magnitude in the visible light spectrum. These findings not only bridge a critical gap between theory and experiment but also pave the way for future technologies where temperature, electric fields, and light dynamically modulate optoelectronic properties, establishing CAP as a versatile platform for energy and photonic applications.

Two-Step Reduction Pathway of Copper(II) by Oleylamine for the Nucleation of Cu(0) Nanoparticles: A Joint Modelling and Experimental Study

Oleylamine is widely used in the synthesis of colloidal nanoparticles, as a solvent, as a stabilizing agent, and sometimes as a reducing agent. For example, metallic nanoparticles are obtained through reduction when Ni(II) and Pd(II) precursors are used or through disproportionation in the case of Ni(I) or Co(I). A similar dichotomy is observed for Cu precursors, with an additional complexity due to the nature of the precursor salt. In the present article, we report a combined DFT evaluation of possible reduction paths for Cu(II) and Cu(I) reduction by oleylamine, including the competition with Cu(I) disproportionation, and X-ray Absorption Spectroscopy monitoring of the oxidation state of copper(II) acetylacetonate in oleylamine. We show that the reduction of copper(II) acetylacetonate goes through a two-steps process, with the intermediate formation of Cu(I) complexes. The role of phosphine ligands is demonstrated as well as the relevance of these findings in case alternative copper sources such as copper halogen salts.

Structural, Optoelectronic, Magnetic, and Photoelectrochemical Consequences of Copper Insertion into Alkaline Earth Metal (Mg, Ca, or Sr) Pyrovanadate Compound Frameworks

This study explores the manifold consequences of introducing copper into an alkaline earth metal (A = Mg, Ca, or Sr) pyrovanadate compound (A2V2O7) framework. Thus, powder X-ray diffraction coupled with Rietveld refinement showed that phase pure alloys, namely, Mg0.67Cu1.33V2O7, CaCuV2O7, and SrCuV2O7 could be obtained via solution combustion synthesis. Local structure distortions from copper insertion into the A2V2O7 compound framework were revealed by Raman spectroscopy and X-ray photoelectron spectroscopy. Importantly, the Cu2-xAxV2O7 alloy framework is shown below to be an excellent platform for demonstrating the complementarity of the two outcomes of bandgap photon absorption, namely, photovoltaic or photoelectrochemical (PEC) activity versus photoluminescence (PL). Thus, PL from the parent pyrovanadate was quenched when copper was introduced; concomitantly, PEC activity emerged for the semiconductor alloys. Changes in the electronic band structures on copper introduction were experimentally probed by diffuse reflectance spectroscopy and Kelvin probe measurements. These data were complemented by density functional theory (DFT) calculations. Finally, the magnetic attributes of the three alloys are discussed via both experiment and theory.

[C2N4H7O][NH2SO3]: High-Performance Ultraviolet Nonlinear Optical Crystal with Ditrigon Coupled Guanylurea Group

The Development of high-performance short-wave ultraviolet (UV) nonlinear optical (NLO) crystals is critical in the field of optoelectronic functional crystals. High-performance NLO functional units are crucial for achieving desired target crystals. In this study, a promising group, guanylurea ([C2N4H7O]+, abbreviated as GU), was investigated using a unit coupling strategy. Furthermore, by modifying the KBe2BO3F2 template structure at the molecular level, the first metal-free guanylurea sulfamate [C2N4H7O][NH2SO3] was successfully synthesized. This crystal achieved an effective balance between the short UV cutoff edge (227 nm), strong second-harmonic generation (SHG) response (6.2×KDP), and large birefringence (0.225@1064 nm). In addition, the remarkable phase-matching capability provides the potential for a fourth-harmonic generation (266 nm) in the Nd: YAG laser. Theoretical calculations indicated that GU and its favorable arrangement were primarily responsible for the large SHG effect and birefringence. Our study demonstrates that the GU group is promising for the development of UV NLO crystals.

Advanced Fabrication of Graphene-Integrated High-Entropy Alloy@Carbon Nanocomposites as Superior Multifunctional Electrocatalysts

High entropy materials exhibit unparalleled reactivity and tunable electrochemical properties, putting them at the forefront of advances in electrocatalysis for water splitting. Their various interfaces and elements are purposefully engineered at the nanoscale, which is essential to enhancing their electrochemical characteristics. The exceptional catalytic efficiency observed in graphene-coated nanoparticles (NPs) with an inner high-entropy alloy (HEA) (HEA@C) is a result of the combined action of several metallic constituents. However, increasing catalytic efficiency is still a very difficult task, particularly when it comes to obtaining precise control over the composition and structure via efficient synthesis techniques. HEA@C NPs exceptional reactivity and adaptable electrochemical characteristics allow them to perform better in slow oxygen evolution (SOE) activities. The novel multilayer graphene-enhanced HEA CoNiFeCuV@C NPs electrocatalyst presented in this work is carbon-based, and transmission electron microscopy (TEM) investigations verify its efficacy. The efficiency of the oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and oxygen reduction reaction (ORR) is greatly increased by this electrocatalyst. The electrocatalytic performance of the core-shell HEA CoNiFeCuV@C NPs is remarkable for HER, OER, and ORR, even though its highly stressed lattice has structural flaws. These catalysts reach a half-wave potential of 0.87 V in 0.1 M HClO4 at a moderate current density of 10 mA cm-2, with HER and OER onset potentials of 20 and 259 mV, respectively. Using cyclic voltammetry scans, the study delves deeper into the material's evolution by examining its morphology, chemical state, and elemental makeup both before and after activation. In addition to introducing novel electrocatalysts, this study significantly enhances our understanding of the deliberate synthesis of multicomponent intermetallic high-entropy alloys.

Bilayer Kagome Ferrimagnet Exhibiting Exceptional Spontaneous Exchange Bias in TbMn6(Ge,Ga)6

Manipulating interlayer interactions in two-dimensional (2D) materials has led to intriguing behaviors. Borrowing these 2D signatures to bulk materials is likely to unlock exceptional properties. Here, we report an emergent 2D-like bilayer Kagome ferrimagnet through reducing the interbilayer magnetic interaction to nearly zero. This concept is realized within bulk TbMn6(Ge,Ga)6 compounds, characterized by an isolated and pure Mn Kagome lattice, simply by the chemical substitution of Ge with Ga. Specifically, the targeted compound TbMn6Ge5Ga1 exhibits a giant spontaneous exchange bias (SEB) of approximately 1.6 T, which is more than twice that observed in known materials. Field-dependent neutron diffraction reveals the robust nature of the compensated ferrimagnetic (FiM), characterized by almost two-thirds of the moments being pinned and irreversible under fields up to 9 T. Through magnetic and structural analysis, alongside theoretical calculations, we demonstrate that the substantial SEB is related to the intense competition between local robust and weak FiM states within the bilayer Kagome configuration, which are stabilized by an incommensurate spin arrangement. The concept of a bilayer Kagome magnet offers new opportunities for discovering attractive properties in 2D-like materials.

Computational Insights into the Structural and Optical Properties of Ag-Based Halide Double Perovskites

Lead-free halide double perovskites (HDP) have attracted enormous attention in recent years due to their low toxicity, excellent stability, tunable optical properties, and extensive range of compositional possibilities they present. In the very broad HDP family, Ag-based materials are of particular interest due to their easy synthesis, stability to light and moisture, and interesting optical properties, especially in the form of nanocrystals. Given the very large compositional space, theoretical studies play a crucial role in providing insights into the most promising dopant and possible defect interactions to guide the synthesis and explain the properties. In this review, we discuss recent theoretical works on Ag-based perovskites with an emphasis on density functional theory (DFT) calculations. The computational methods and tools are evaluated, assessing their relative strengths and limitations in their ability to clarify experimental results. We focus specifically on how lattice defects influence the structure and properties of HDP, including lattice and thermodynamic stability, band gap tuning, and photoluminescence.

Simple Linear Regression Models for Prediction of Ionization Energies, Electron Affinities, and Fundamental Gaps of Atoms and Molecules

Linear regression equations were developed for different density functionals using data from the CCCBDB, along with a test set of 89 ionization energies (IE) and 76 electron affinities (EA) so that experimental IE and EA can be predicted from orbital energies. Separate equations were determined for different classes of atoms and molecules. These relationships were also applied to all occupied orbitals to simulate the photoemission spectra of organic molecules with accuracy similar to that of other computational methods at a fraction of the cost. The error for large molecules (up to 200 atoms) can be below 0.2 eV with many functionals for the prediction of the IE and EA.

Tailoring frustrated Lewis pair catalysts for enhanced electrochemical CO2 reduction to multi-carbon fuels

Electrochemical reduction of CO2 to value-added chemical fuels is crucial for closing the anthropogenic carbon cycle and storing renewable energy; however, the development of a highly active and selective catalyst remains a significant challenge. Currently, CO2 reduction to hydrocarbons (especially C2 products) mainly relies on copper (Cu)-based catalysts, which often face considerable obstacles, including high energy barriers for C-C coupling and low product selectivity. In this study, we propose an innovative approach by introducing a metal-free frustrated Lewis pair (FLP) catalyst that utilizes the (110) surface of boron phosphide (BP) and boron arsenide (BAs) based on extensive first-principles calculations. Our findings reveal that these surface FLPs of BP and BAs (110) exhibit remarkable stability in electrochemical environments and efficiently capture and activate CO2 molecules through Lewis acid-base interactions. The "push-pull effect" facilitates the reduction of captured CO2 into CH4 and C2H6, featuring ultra-low potential-determining steps (PDS) of 0.11 and 0.28 eV, respectively. Furthermore, the unwanted competitive reaction, i.e. the hydrogen evolution reaction (HER), can be significantly suppressed during CO2 reduction, enhancing the selectivity for desired products. Overall, such a low PDS has never been achieved on any previously reported CO2 reduction catalysts, highlighting the potential of FLPs as a promising strategy for improving the catalytic performance of CO2 reduction reactions.

Nonempirical Adiabatic Connection Correlation Functional from Hartree-Fock Orbitals

We present a nonempirical strategy to construct a correlation functional rooted in the Møller-Plesset (MP) adiabatic connection (AC) formalism for the strong-interaction regime, which satisfies both the weak- and strong-interaction limits and describes accurately the uniform electron gas (UEG) model. The functional is based on Hartree-Fock (HF) orbitals and employs only the UEG and helium atom as model systems; thus, it can be considered a nonempirical and nonlinear generalization of post-HF approaches based on the second-order perturbation theory (MP2) correlation. The functional describes the correlation of atoms with 1 mHa/electron accuracy, and it is also accurate for jellium surface energies. Accurate tests using a nearly complete basis set on diverse systems and properties (atomization/interaction energies, dispersion forces, and ionization potentials) have shown an excellent performance of the functional that corrects the MP2 overbinding without error cancellation. The present investigation can open the way for the development of a new generation of post-HF functionals based on nonlinear MP2 contributions and strong-correlation ingredients.

Two-dimensional Janus X2SSe (X = Al, Ga or In) monolayers: potential photocatalysts with low effective mass

Janus 2D materials with high-efficiency solar energy conversion possess fine photocatalytic properties, which are current research hotspots in the field of photocatalysis. Herein, Janus X2SSe (X = Al, Ga or In) monolayers were proposed to explore their photocatalytic activities through first-principles calculation. The results demonstrated that the structures of Janus X2SSe (X = Al, Ga or In) monolayers were both dynamically and thermodynamically stable and exhibited excellent semiconductor properties. Additionally, a low effective mass for the photogenerated electrons and holes was observed. However, the Janus Al2SSe monolayer had an inappropriate band-edge potential, and the light-absorption edge corresponding to the maximum wavelength of the Janus Ga2SSe monolayer was not wide enough, which did not meet the conditions for an effective photocatalyst. Amazingly, the Janus In2SSe monolayer not only completely met the redox conditions for photocatalytic water decomposition but also presented visible-optical absorption with an absorption-band edge at 662 nm because of its indirect band gap of 1.52 eV, revealing its great application potential in photocatalysis. The above findings disclose the potential of the Janus In2SSe monolayer as a high-performance photocatalyst.

Electrocatalytic CO2 Reduction Empowered by 2D Hexagonal Transition Metal Borides

Electrocatalysis holds immense promise for producing high-value chemicals and fuels through the carbon dioxide reduction reaction (CO2RR), advancing global sustainability and carbon neutrality. However, conventional electrocatalysts based on transition metals are often limited by significant overpotentials. Since the discovery of the first hexagonal MAB (h-MAB) phase, Ti2InB2, and its 2D derivative in 2019, 2D hexagonal transition metal borides (h-MBenes) have emerged as promising candidates for various electrochemical applications. This study presents the first theoretical investigation into the CO2RR catalytic properties of pristine h-MBenes (h-MB) and their ─O (h-MBO) and ─OH (h-MBOH) terminated counterparts, focusing on metals such as Sc, Ti, V, Zr, Nb, Hf, and Ta. These results reveal while h-MB and h-MBO exhibit poor catalytic performance due to overly strong or weak interactions with CO2, h-MBOH shows great promise. Notably, ScBOH, TiBOH, and ZrBOH display exceptionally low limiting potentials (UL) of -0.46, -0.53, and -0.64 V, respectively. These findings uncover the unique role of ─OH in tuning the electronic properties of h-MBenes, thereby optimizing intermediate adsorption, which prevents excessive binding and enhances catalytic efficiency. This research offers valuable insights into the potential of h-MBenes as highly efficient CO2RR catalysts, underscoring their versatility and significant prospects for electrochemical applications.

Surface Engineering Enabling Efficient Upcycling of Highly Degraded Layered Cathodes

Direct recycling of cathode materials has attracted phenomenal attention due to its economic and eco-friendly advantages. However, existing direct recycling technologies are difficult to apply to highly degraded layered materials as the accumulation of thick rock-salt phases on their surfaces not only blocks lithiation channels but also is thermodynamically difficult to transform into layered phases. Here, a surface engineering-assisted direct upcycling strategy that reactivates the lithium diffusion channels at the highly degraded cathode surfaces using acid etching explored. Acid can selectively remove the electrochemically inert rock-salt phases on the surface while simultaneously dissociating the degraded polycrystalline structure to single crystals, thereby reducing the thermodynamic barrier of the relithiation process and enhancing the stability of the regenerated cathode. This strategy can restore the capacity of highly degraded LiNi0.5Co0.2Mn0.3O2 from 59.7 to 165.4 mAh g-1, comparable to that of commercialized ones. The regenerated cathode also exhibits excellent electrochemical stability with a capacity retention of 80.1% at 1 C after 500 cycles within 3.0-4.2 V (vs graphite) in pouch-type full cells. In addition, the generality of this strategy has also been validated on Ni-rich layered materials and LiCoO2. This work presents a promising approach for direct recycling of highly degraded cathode materials.

Electrodeposited P-Doped CuNi Alloy from Deep Eutectic Solvent for Efficient and Selective Nitrate-to-Ammonia Electroreduction

Electrochemical nitrate reduction reaction (NO3RR) offers a promising alternative for ammonia production using electricity generated from renewable energy sources. Active electrocatalysts with high selectivity and high yield are required to selectively catalyze NO3RR to ammonia. Here, P-doped Cu0.51Ni0.49 alloy thin films are electrodeposited from a deep eutectic solvent of choline chloride-ethylene glycol (ChCl/EG). The P-Cu0.51Ni0.49 produces 1616.94 µg h-1 cm-2 of ammonia at -0.55 VRHE (V versus reversible hydrogen electrode), with a Faradaic efficiency of 98.38% and ammonia selectivity of 97.84% at -0.25 VRHE, much better than the P-Ni and P-Cu prepared under similar condition. The high ammonia production rate, Faradaic efficiency and selectivity are originated from high number of electrochemically active sites and more facile kinetics. Mechanistic study and density functional theory calculation proves that P-Cu0.51Ni0.49 exhibits higher conductivity and more facile NO3 - adsorption compared to P-Ni and P-Cu, induced by the electron interaction. Characterizations after NO3RR cycling show that the crystallinity of P-Cu0.51Ni0.49 decreases, with the content of divalent metal ions increases at the surface. The P-Cu0.51Ni0.49 is an active and stable material to electrocatalyze NO3RR to ammonia in neutral aqueous solutions.