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Excitons, bound electron-hole pairs, influence the optical properties in strongly interacting solid-state systems and are typically most stable and pronounced in monolayer materials. Bulk systems with large exciton binding energies, on the other hand, are rare and the mechanisms driving their stability are still relatively unexplored. Here, we report an exceptionally large exciton binding energy in single crystals of the bulk van der Waals antiferromagnet CrSBr. Utilizing state-of-the-art angle-resolved photoemission spectroscopy and self-consistent ab-initio GW calculations, we present direct spectroscopic evidence supporting electronic localization and weak dielectric screening as mechanisms contributing to the amplified exciton binding energy. Furthermore, we report that surface doping enables broad tunability of the band gap offering promise for engineering of the optical and electronic properties. Our results indicate that CrSBr is a promising material for the study of the role of anisotropy in strongly interacting bulk systems and for the development of exciton-based optoelectronics. Chromium sulfur bromide is an air-stable van der Waals magnet, which has a large optical response. Here, Smolenski et al find a large exciton binding energy CrSBr, which they attribute to localization due to the quasi one-dimensional electronic bands. [ABSTRACT FROM AUTHOR]

Developing affordable thermoelectric (TE) materials is critical for efficient waste heat recovery in industries. With the goal of developing novel, affordable TE materials, the present experimental–theoretical investigation, for the first time, presents a rigorous analysis of the electrical and thermal transport properties of a multi-principal-component AlCuFeMn alloy (MPCA). TE properties related to electronic transport, including the Seebeck coefficient, electrical conductivity, and thermal conductivity, were measured on a vacuum-cast sample and were computed using semi-classical Boltzmann transport theory. Additionally, ab initio calculations were performed to calculate the lattice thermal conductivity. The alloy demonstrated overall thermal conductivity of < 4 W/mK, comparable to conventional thermoelectric materials, while the computed lattice thermal conductivity was < 1 W/mK. Such low thermal conductivity may be attributed to the complex microstructure as well as the uniform distribution of aluminium in the matrix. The power factor of the alloy, however, was small (< 0.1 mW/mK2), translating to a low figure of merit (ZT ~ 0.01). Our study indicates that composition engineering can potentially improve the power factor and thus the overall TE response in an AlCuFeMn alloy. [ABSTRACT FROM AUTHOR]

Using ab initio calculations, the structural and photoelectric properties of γ-GeSe with B, C, and N adsorption were systematically investigated. The atomic structure relaxations show that B, C, and N are preferentially located on the lower hexagonal hollow, upper hexagonal hollow, and on top of Se, respectively. The adsorption with B, C, and N can induce defective bands between the energy region n of the valence bands and the conduction bands, and all the systems with adatoms are magnetic, with 1 μB, 2 μB, and 1 μB magnetic moments, respectively, which are mainly caused by the hybridization between adatoms and the adjacent Ge and Se atoms. Based on the spin-polarized band structure, we find that C-adsorbed γ-GeSe is metallic, while γ-GeSe with B and N adatoms is half-metallic, with 100% spin polarization at the Fermi level. Furthermore, owing to the electronic structural differences between spin-up and spin-down sections of B- and N-adsorbed γ-GeSe, the light in the low-energy region (< 1.0 eV) can only cause electronic excitations in one spin channel, giving rise to interesting spin-polarized photoelectric properties. Our results suggest that γ-GeSe with B, C, and N adsorption is a promising candidate for spintronic photoelectric device applications. [ABSTRACT FROM AUTHOR]

Prediction and discovery of new materials with desired properties are at the forefront of quantum science and technology research. A major bottleneck in this field is the computational resources and time complexity related to finding new materials from ab initio calculations. In this work, an effective and robust deep learning-based model is proposed by incorporating persistent homology with graph neural network which offers an accuracy of 91.4 % and an F1 score of 88.5 % in classifying topological versus non-topological materials, outperforming the other state-of-the-art classifier models. Additionally, out-of-distribution and newly discovered topological materials can be classified using our method with high confidence. The incorporation of the graph neural network encodes the underlying relation between the atoms into the model based on their crystalline structures and thus proved to be an effective method to represent and process non-Euclidean data like molecules with a relatively shallow network. The persistent homology pipeline in the proposed neural network integrates a topological analysis of crystal structures into the deep learning model, enhancing both robustness and performance. Our classifier can serve as an efficacious tool for predicting the topological class, thereby enabling a high-throughput search for fascinating topological materials. [ABSTRACT FROM AUTHOR]

The 14N nuclear quadrupole resonance (NQR) spectra of two common benzodiazepines, Diazepam and Lorazepam, have been recorded using cross relaxation double resonance. Benzodiazepines are characterized by a fused diazepine and benzene ring and act as central nervous system depressants or tranquilizers. Each compound has two distinct nitrogen atoms in their molecular structure. Both nitrogen atoms of diazepam have similar asymmetry parameters. However, the imine nitrogen of diazepam has a slightly higher quadrupole coupling constant (χ) than its tertiary amide nitrogen. The 14N NQR signals of lorazepam suggests that there is more than one form present in the solid. The imine nitrogen shows similar frequencies and NQR parameters to that of diazepam. However, the frequencies assigned to the secondary amide nitrogen result in a lower χ and a relatively higher asymmetry parameter (η) than the amide nitrogen of diazepam. This has been attributed to hydrogen bonding of the amide proton in lorazepam. Ab-initio and DFT calculations have been performed to support the assignments. [ABSTRACT FROM AUTHOR]

Based on the first-principles density-functional theory, formation energies, transition energy levels of M (M = Mo, W) doped α-BiNbO4 systems are studied. The calculation results show that the donor defects form easily under Bi-rich condition. Of these, the Wint (W interstitial) and Moint (Mo interstitial) are the two main defects that lead to n-type conductivity. Then, the electronic structures of M-mono-doped and M/Ovac (O vacancy)-codoped α-BiNbO4 were investigated. Our results show that the band gap of Wint/Ovac-codoped α-BiNbO4 is reduced by 0.43 eV, and the conduction band minimum and valence band maximum are reduced by 0.20 and 0.23 eV, respectively, compared to pure α-BiNbO4, with less driving force required for the redox reaction process and then an increased redox rate. The α-BiNbO4 with Wint+Ovac defects with n-type conductivity has good photocatalytic activity in water splitting. [ABSTRACT FROM AUTHOR]

We present a computational study based on the Density Functional Theory (DFT) of the magnetic and structural properties of the cobalt ferrite (CoFe2O4). Using ab initio calculations, the electronic structure has been analyzed, and the structural and magnetic ground states were obtained by considering the antiferromagnetic and ferromagnetic coupling in normal spinel and inverse spinel structures, taking into account different cationic distributions at the last one. Furthermore, to understand the effect of the DFT + U calculation, an analysis of the charge distribution and the change of density of states (DoS) parameters, including the bandgap and magnetic moment, was performed. In addition, a clear dependence of the magnetic moment per atom and band gap energy on the Hubbard parameter (U) was observed, with optimal values in GGA + U identified as UFe = 4 eV and UCo = 4 eV. Finally, the electronic rearrangement of the outermost energy levels of the valence band (3d-orbitals) was evidenced when the Hubbard parameter was applied. [ABSTRACT FROM AUTHOR]

Halogenated cycloalkanes (cyc-CnXs, n = 4, 5 & 6 and X = H, F & Cl) benefit the environment and the economy. These chemicals have various industrial and agricultural applications due to their low Global Warming Potential (GWP) and negligible ozone depletion Potential (ODP). This study uses ab initio methods, MP2, and density functional theory (B3LYP, M06-2X, and ωB97x-D) to investigate the atmospheric impacts. Utilizing these methodologies, we have calculated radiative efficiencies (REs), Global Warming Potential (GWP), Global Temperature change Potential (GTP), integrated Global Temperature change Potential (iGTP), ozone depletion Potential (ODP), photo ozone creation Potential (POCP), and acidification Potential (AP) of cyc-CnXs (n = 4, 5 & 6 and X = H, F & Cl) compounds. For atmospheric reactivity analysis (NCI, MEP, and FMO), we employed the ωB97x-D/def2-TZVP level of theory. FMO analysis demonstrated that cyclo-α-C6H6Cl6 and cyclo-γ-C6H6Cl6 have a reduced energy gap and higher reactivity than other chemicals. Ab initio and DFT calculations conclude that several fluorine atom-containing molecules always have a significant radiative efficiency value. We have evaluated the cyc-CnXs (n = 4, 5 & 6 and X = H, F & Cl) dielectric strength (DS). We have found none of them could be used as an insulating material to replace SF6. [ABSTRACT FROM AUTHOR]

The shape of ions of quaternary ammonium bases should be known to correctly interpret the properties of their salts; however, there is almost no available numerical data on geometric parameters of their molecules. We report ab initio (HF/6-31G) calculation data on the structure of an all-atom model of the cluster containing one ion pair of tetrabutylammonium bromide TBA+Br– in a vacuum and in a water environment. The same calculations are performed for its neutral structural analogue tetrabutylmethane (TBM). The following geometric parameters are reported: distances from the central atom to the terminal carbon and hydrogen atoms; distances between terminal atoms; excess charges on hydrogen atoms and angles between atoms characterizing the structure; volumes of structures approximating real species; average numbers and lengths of hydrogen bonds in water molecules depending on the distance to the central atom of the species. It is shown that the determined shapes correspond to irregular tetrahedra with densely packed hydrocarbon radicals. The shape and size of TBA+ and TBM are almost identical and do not depend on the environment or the electric charge on the central atom. [ABSTRACT FROM AUTHOR]

This research focuses on the theoretical investigation of the structural, elastic, electronic, and optical properties of alkali metal tetrafluoroaurate NaAuF4, KAuF4, and RbAuF4 ternary compounds through ab-initio calculations within the framework of density functional theory using the pseudopotential plane wave method. The structural parameters are consistent with the experimental values reported in the literature. Since these compounds are ductile by nature, the elastic constants support this claim. Numerous anisotropy indexes are examined in order to validate the elastic anisotropic nature of these materials. Furthermore, employing 3D shapes has allowed for the implementation of additional innovative approaches. These materials can be classified as semiconductors based on their computed electronic structure. In contrast to KAuF4 and RbAuF4, which are semiconductor materials with an indirect band gap, NaAuF4 is a semiconductor with a direct band gap. Finally, in-depth research has been done on optical properties, including the real and imaginary components of the dielectric function, the refractive index, and the absorption coefficient. Due to their broad optical absorption in the UV range, these materials may be useful for the manufacture of UV photodetectors. Unfortunately, there is no comparable earlier study available. Hence, upcoming experimental investigations are anticipated to be inspired by this theoretical research. [ABSTRACT FROM AUTHOR]

Comprehensive structural and electronic properties of zircon-type ternary-metal oxide, dysprosium orthovanadate, doped with varying concentrations of Er have been investigated using first-principles density functional theory (DFT). Furthermore, the significance of substitutional site doping has been elucidated, revealing that Er incorporation can profoundly alter the structural and electronic characteristics of DyVO4. Replacing Er atoms with Dy atoms through substitutional doping reduces the band gap to 2.79 eV compared to the pure zircon-type dysprosium vanadate oxide's band gap value of 2.87 eV. Cohesive energy of Er-doped DyVO4 oxide has also been computed at the ab initio level of calculation. Partial density of states' (PDOS) calculations of all configurations, suggest that the doping element Er exhibits favourable chemical interactions with the host metal oxide, DyVO4. Electronic bands near the zero-energy or Fermi level strongly originate from the molecular orbitals of O, V and Dy atoms. Still, we have found that cation substitution at Dy ions' site largely influences these electronic states and decreases band gap energy value. Consequently, by adjusting concentration of the dopant, the band gap of DyVO4 oxide can be finely tuned to achieve specific desired levels, which is suitable for electronic applications. [ABSTRACT FROM AUTHOR]

The driving force of a charge density wave (CDW) transition in quasi-two dimensional systems is still debated, while being crucial in understanding electronic correlation in such materials. Here we use femtosecond time- and angle-resolved photoemission spectroscopy combined with computational methods to investigate the coherent lattice dynamics of a prototypical CDW system. The photo-induced temporal evolution of the periodic lattice distortion associated with the amplitude mode reveals the dynamics of the free energy functional governing the order parameter. Our approach establishes that optically-induced screening rather than CDW melting at the electronic level leads to a transiently modified potential which explains the anharmonic behaviour of the amplitude mode and discloses the structural origin of the symmetry-breaking phase transition. The charge density wave (CDW) formation mechanisms in 2D and quasi-2D systems are still highly debated. Here, the authors combine time-resolved ARPES and ab initio calculations to map the free energy functional in the prototypical CDW compound 1T-TaSe2 concluding that the CDW state is driven by structural rather than electronic instabilities. [ABSTRACT FROM AUTHOR]

In this work, we predicted two different configurations of fullerene nanoribbons (quasi-hexagonal phase (qHP) and quasi-tetragonal phase (qTP)) based on two-dimensional fullerenes, with widths of 1, 2, and 3 fullerene units, respectively. Based on first-principles calculations and ab-initio molecular dynamics (AIMD), the thermal stability and optical properties of six fullerene nanoribbons were predicted. AIMD studies indicate that wider qHP nanoribbons (qHPs) exhibit better thermal stability, while increased temperatures lead to greater instability. In contrast, qHP-3 shows the best thermal stability among the six structures. Then, the optical gap between the calculated and experimental quasi-hexagonal two-dimensional fullerenes is compared to illustrate the accuracy of the calculation. The absorption spectra of six fullerene nanoribbons were calculated and the anisotropy of light absorption was analyzed. Finally, the charge transfer modes of each excited state were visualized through electron-hole density plots. This work provides an essential theoretical foundation for understanding new all-carbon materials, specifically fullerenes. [ABSTRACT FROM AUTHOR]

Noncollinear dipole textures greatly extend the scientific merits and application perspective of ferroic materials. In fact, noncollinear spin textures have been well recognized as one of the core issues of condensed matter, e.g. cycloidal/conical magnets with multiferroicity and magnetic skyrmions with topological properties. However, the counterparts in electrical polarized materials are less studied and thus urgently needed, since electric dipoles are usually aligned collinearly in most ferroelectrics/antiferroelectrics. Molecular crystals with electric dipoles provide a rich ore to explore the noncollinear polarity. Here we report an organic salt (H2Dabco)BrClO4 (H2Dabco = N,N'−1,4-diazabicyclo[2.2.2]octonium) that shows a transition between the ferroelectric and antiferroelectric phases. Based on experimental characterizations and ab initio calculations, it is found that its electric dipoles present nontrivial noncollinear textures with 60o-twisting angle between the neighbors. Then the ferroelectric-antiferroelectric transition can be understood as the coding of twisting angle sequence. Our study reveals the unique science of noncollinear electric polarity. The authors find that the electric dipoles of a hybrid molecular material exhibit two kinds of intrinsic noncollinear textures, corresponding to its ferroelectric and antiferroelectric states. [ABSTRACT FROM AUTHOR]

Molecular dynamics (MD) is an indispensable atomistic-scale computational tool widely-used in various disciplines. In the past decades, nearly all ab initio MD and machine-learning MD have been based on the general-purpose central/graphics processing units (CPU/GPU), which are well-known to suffer from their intrinsic "memory wall" and "power wall" bottlenecks. Consequently, nowadays MD calculations with ab initio accuracy are extremely time-consuming and power-consuming, imposing serious restrictions on the MD simulation size and duration. To solve this problem, here we propose a special-purpose MD processing unit (MDPU), which could reduce MD time and power consumption by about 103 times (109 times) compared to state-of-the-art machine-learning MD (ab initio MD) based on CPU/GPU, while keeping ab initio accuracy. With significantly-enhanced performance, the proposed MDPU may pave a way for the accurate atomistic-scale analysis of large-size and/or long-duration problems which were impossible/impractical to compute before. [ABSTRACT FROM AUTHOR]

Context: The strength and nature of the two halogen bonds in the NCI···CH3I···−CN halogen-bonded ternary complex are studied in the gas phase via ab initio calculations. Different indicators of halogen bond strength were employed to examine the interactions including geometries, complexation energies, Natural Bond Order (NBO) Wiberg bond indices, and Atoms in Molecules (AIM)-based charge density topological properties. The results show that the halogen bond is strong and partly covalent in nature when CH3I donates the halogen bond, but weak and noncovalent in nature when CH3I accepts the halogen bond. Significant halogen bond cooperativity emerges in the ternary complex relative to the corresponding heterodimer complexes, NCI···CH3I and CH3I···−CN, respectively. For example, the CCSD(T) complexation energy of the ternary complex (-18.27 kcal/mol) is about twice the sum of the complexation energies of the component dimers (-9.54 kcal/mol). The halonium transfer reaction that converts the ternary complex into an equivalent one was also investigated. The electronic barrier for the halonium transfer was calculated to be 6.70 kcal/mol at the CCSD(T) level. Although the MP2 level underestimates and the MP3 overestimates the barrier, their calculated MP2.5 average barrier (6.44 kcal/mol) is close to that of the more robust CCSD(T) level. Insights on the halonium ion transfer reaction was obtained by examining the reaction energy and force profiles along the intrinsic reaction coordinate, IRC. The corresponding evolution of other properties such as bond lengths, Wiberg bond indices, and Mulliken charges provides specific insight on the extent of structural rearrangements and electronic redistribution throughout the entire IRC space. Methods: The MP2 method was used for geometry optimizations. Energy calculations were performed using the CCSD(T) method. The aug-cc-pVTZ basis set was employed for all atoms other than iodine for which the aug-cc-pVTZ-PP basis set was used instead. [ABSTRACT FROM AUTHOR]

This paper presents a theoretical investigation utilizing the full-potential linearized augmented planewave method (FP-LAPW) within density functional theory (DFT) framework, implemented in the Wien2k program. Analysis reveals that Sr2DySbO6 (t = 0.991) and Sr2LaSbO6 (t = 1.01) exhibit theoretical tolerance factors suggesting their crystallization in a face-centered cubic form (FCC) with space group (Fm3m; No. 225). Notably, Sr2DySbO6 demonstrates a slightly higher stability (χ_ value of 2.1207) compared to Sr2LaSbO6 (χ_ value of 1.9902). Both compounds also show negative formation energies, suggesting that they are feasible for experimental synthesis and structurally stable. Stability is further confirmed by structural optimization by atomic relaxation and total energy reduction against unit cell volume. Both compounds exhibit ductility, anisotropy, ionic bonding nature, elastic stability, resistance to plastic deformation, and central force crystal properties. Sr2DySbO6 electronic characteristics reveals that it is metallic, whereas Sr2LaSbO6 is insulating. Energy-wise, optical properties are assessed between 0 and 15 eV. Both the compounds have demonstrated noteworthy UV responses are making use of the unique characteristics and high energy of UV light for a range of creative uses. Overall, these findings advocate for experimental exploration of these compounds, hinting at potential applications. [ABSTRACT FROM AUTHOR]

This study investigates the structural, optoelectronic, magnetic and thermophysical properties of three newly designed semiconductor pyrochlore oxides, namely RE2Ti2O7 (RE = Er, Eu, Tb), using ab-initio calculations within the density functional theory framework. The values of indirect bandgaps are 3.8, 2.2 and 3.77 eV for the spin up channel of Er2Ti2O7, Eu2Ti2O7, and Tb2Ti2O7, respectively. While the values of indirect bandgaps for the spin down channel of Er2Ti2O7, Eu2Ti2O7, and Tb2Ti2O7 are 3.56, 3.65 and 2.1 eV, respectively. The paramagnetic magnetic moments can be inferred by analyzing the distinct band shapes observed in the energy band structures of the studied compounds corresponding to the spin up and spin down states. The magnetic moments of Er2Ti2O7, Eu2Ti2O7, and Tb2Ti2O7 have significant magnitudes, specifically measuring 12.00, 24.51, and 24.00 μ B , respectively. Significant absorption of incident photons by the studied compounds can be noted in near UV region in both spin channels. Low reflectivity (~ 30%) by RE2Ti2O7 (RE = Er, Eu, Tb) is evident from the R (ω) spectra in an energy range of 1.0–10.0 eV. However, these compounds exhibit ~ 50% reflectance of the incident photons in upper UV region (above 10.0 eV). The analysis of the Seebeck coefficient spectra reveals that RE2Ti2O7 (RE = Er, Eu, Tb) exhibits p-type semiconductor behavior, however, Eu2Ti2O7 also shows n-type behavior from 200 to 450 K. The presented thermodynamic characteristics reveal that the pyrochlore oxides RE2Ti2O7 (RE = Er, Eu, Tb) exhibit thermal stability. [ABSTRACT FROM AUTHOR]

High-harmonic generation (HHG) has emerged as a central technique in attosecond science and strong-field physics, providing a tool for investigating ultrafast dynamics. However, the microscopic mechanism of HHG in solids is still under debate, and it is unclear how it is modified in the ubiquitous presence of phonons. Here we theoretically investigate the role of collectively coherent vibrations in HHG in a wide range of solids (e.g., hBN, graphite, 2H-MoS2, and diamond). We predict that phonon-assisted high harmonic yields can be significantly enhanced, compared to the phonon-free case – up to a factor of ~20 for a transverse optical phonon in bulk hBN. We also show that the emitted harmonics strongly depend on the character of the pumped vibrational modes. Through state-of-the-art ab initio calculations, we elucidate the physical origin of the HHG yield enhancement – phonon-assisted photoinduced carrier doping, which plays a paramount role in both intraband and interband electron dynamics. Our research illuminates a clear pathway toward comprehending phonon-mediated nonlinear optical processes within materials, offering a powerful tool to deliberately engineer and govern solid-state high harmonics. [ABSTRACT FROM AUTHOR]

The conversion efficiency from charge current to spin current via the spin Hall effect is evaluated by the spin Hall ratio (SHR). Through state-of-the-art ab initio calculations involving both charge conductivity and spin Hall conductivity, we report the SHRs of the III-V monolayer family, revealing an ultrahigh ratio of 0.58 in the hole-doped GaAs monolayer. In order to find more promising 2D materials, a descriptor for high SHR is proposed and applied to a high-throughput database, which provides the fully relativistic band structures and Wannier Hamiltonians of 216 exfoliable monolayer semiconductors and has been released to the community. Among potential candidates for high SHR, the MXene monolayer Sc2CCl2 is identified with the proposed descriptor and confirmed by computation, demonstrating the descriptor validity for high SHR materials discovery. [ABSTRACT FROM AUTHOR]

Incorporation of the trimethoxyphenyl group at position 7 of flavin can drastically change the photophysical properties of flavin. We show unique fast singlet 1(π,π*) excited state deactivation pathway through nonadiabatic transition to the 1(n,π*) excited- state, and subsequent deactivation to the ground electronic state (S0), closing the photocycle. This mechanism explains the exceptionally weak fluorescence and the short excited–state lifetime for the flavin trimethoxyphenyl derivative and the lack of excited triplet T1 state formation. Full recovery of flavin in its ground state takes place within a 15 ps time window after photoexcitation in a polar solvent such as acetonitrile. According to quantum chemical calculations, the C(2)-O distance elongates by 0.16 Å in the 1(n,π*) state, with respect to the ground state. Intermediate–state structures are predicted by theoretical ab initio calculations and their dynamics are investigated using broadband vis-NIR time-resolved transient absorption and fluorescence up-conversion techniques. [ABSTRACT FROM AUTHOR]

Phonon engineering is crucial for thermal management in GaN-based power devices, where phonon-defect interactions limit performance. However, detecting nanoscale phonon transport constrained by III-nitride defects is challenging due to limited spatial resolution. Here, we used advanced scanning transmission electron microscopy and electron energy loss spectroscopy to examine vibrational modes in a prismatic stacking fault in GaN. By comparing experimental results with ab initio calculations, we identified three types of defect-derived modes: localized defect modes, a confined bulk mode, and a fully extended mode. Additionally, the PSF exhibits a smaller phonon energy gap and lower acoustic sound speeds than defect-free GaN, suggesting reduced thermal conductivity. Our study elucidates the vibrational behavior of a GaN defect via advanced characterization methods and highlights properties that may affect thermal behavior. Authors identify three types of defect-derived phonon modes in GaN, including localized defect modes, a confined bulk mode, and a fully extended mode. The defects exhibit a smaller phonon energy gap and lower sound speeds, indicating reduced thermal conductivity. [ABSTRACT FROM AUTHOR]

This review provides a survey of computational methods generally used in the evaluation of the corrosion inhibition evaluation of metallic materials in various environments. Herein a general overview of corrosion inhibition is given, thereafter, a discussion of the most widely used computational methods is given which include; molecular dynamics (MD) simulations, Monte Carlo (MC) simulations, density functional theory (DFT), Semi-empirical methods and first-principles calculations and Ab initio (Hartree Fock) calculations. A comparison of comparative analysis of experimental and computational approaches in corrosion inhibition studies was given after which the prospects of the use of computational methods in corrosion science were discussed. Overall, each of these methods has its strengths and limitations, but when used in combination, they are capable of providing a holistic understanding of corrosion inhibition mechanisms. [ABSTRACT FROM AUTHOR]

Interpreting Raman and IR vibrational spectra in complex organic molecules lacking symmetries poses a formidable challenge. In this study, we propose an innovative approach for simulating vibrational spectra and attributing observed peaks to molecular motions, even when highly anharmonic, without the need for computationally expensive ab initio calculations. Our approach stems from the time-dependent stochastic self-consistent harmonic approximation to capture quantum nuclear fluctuations in atom dynamics while describing interatomic interaction through state-of-the-art reactive machine-learning force fields. Finally, we employ an isotropic charge model and a bond capacitor model trained on ab initio data to predict the intensity of IR and Raman signals. [ABSTRACT FROM AUTHOR]

The analysis in the present paper is based on the most known concept introduced by the brilliant physicist Alexander Andreev: Andreev bound states in a normal metal sandwiched between two superconductors. The paper presents results of direct calculations of ab initio expressions for the currents in a long ballistic SNS junction. The expressions are expanded in 1/L (L is the thickness of the normal layer). The main contribution ∝ 1 / L to the current agrees with the results obtained in the past, but the analysis suggests a new physical picture of the charge transport through the junction free from the problem with the charge conservation law. The saw-tooth current-phase relation at T = 0 directly follows from the Galilean invariance of the Bogolyubov–de Gennes equations proved in the paper. The proof is valid for any variation of the energy gap in space if the Andreev reflection is the only scattering process. The respective roles of the contributions of bound and continuum states to the current are clarified. They depend on the junction dimensionality. [ABSTRACT FROM AUTHOR]

Context: 1,1- and 1,2-ethenedithiol are elusive systems that could potentially exist in interstellar space, similar to analogous diols. In this paper, we investigate the structure, stability, and bonding characteristics of these compounds as well as the ions produced by protonation, deprotonation, or simple ionization processes. 1,2-ethenedithiol has two isomers, Z and E, with the most stable conformer being syn-anti for the Z isomer and anti-anti for the E isomer. However, the energy gaps between the different conformers are never larger than 6 kJ·mol−1. For 1,1-ethenedithiol, the global minimum is the syn-anti conformer. The vertical and adiabatic ionization processes as well as the intrinsic basicities and acidities of these families of compounds were analyzed and compared with those of the corresponding diols previously reported in the literature. This comparison revealed not only the numerical differences in these thermodynamic properties but also distinct trends between the two families of compounds. Methods: State-of-the-art G4 ab initio calculations were employed to calculate the structures and total energies of the systems under investigation. The QTAIM, ELF, and NBO approaches were used to analyze the electron density of all the neutral and charged systems included in our study. Van der Waals contributions, when relevant, were analyzed by locating regions of low reduced density gradient(s) using the NCIPLOT approach. [ABSTRACT FROM AUTHOR]

We present a new wide-ranging correlation for the viscosity of nitrogen based on critically evaluated experimental data as well as ab-initio calculations. The correlation is designed to be used with densities from an existing equation of state, which is valid from the triple point to 1000 K, at pressures up to 2200 MPa. The estimated uncertainty (at the 95% confidence level) for the viscosity varies depending on the temperature and pressure, from a low of 0.2% in the dilute-gas range near room temperature, to 4% for the liquid phase at pressures from saturation up to 34 MPa, and maximum of 8% in the supercritical region at pressures above 650 MPa. Extensive comparisons with experimental data are provided. [ABSTRACT FROM AUTHOR]

This paper first uses ab initio calculations for a systematic study of an influence of Cr, Mn, C, and P alloying elements on the grain boundary segregation of phosphorus in ferromagnetic α-Fe and its dependence on the nature of grain boundaries. Segregation energies of each element and site are fully calculated for two special grain boundaries of the types Σ3(111) and Σ5(310). We study the effect of grain boundary type on the segregation process of alloying elements. The estimate of effective segregation energy for each model of grain boundaries from the obtained segregation energies and analysis of the alloying element distribution at various boundary points are carried out. The paper shows that the Voronoi volume of a Fe site at the segregation point determines the segregation energy of the elements under study. The segregation energies of various pairs of impurities on the boundary are calculated. The effect of substitutional impurities on the change in the segregation energy of phosphorous atoms at the interstitial and substitutional sites and the effect of the phosphorous atom on the change in the impurity segregation energy at various boundary points are studied. The results obtained in this study correspond closely to the available experimental data and provide important base data for the design of high strength steel materials, and are useful for understanding the effect of alloying elements on bcc Fe. [ABSTRACT FROM AUTHOR]

Ammonium fluoride (NH₄F) exhibits a variety of crystalline phases depending on temperature and pressure. By employing Raman spectroscopy and synchrotron X-ray diffraction beyond megabar pressures (up to 140 GPa), we have here observed a novel dense solid phase of NH₄F, characterised by the tetragonal P4/nmm structure also observed in other ammonium halides under less extreme pressure conditions, typically a few GPa. Using detailed ab-initio calculations and reevaluating earlier theoretical models pertaining to other ammonium halides, we examine the microscopic mechanisms underlying the transition from the low-pressure cubic phase (P-43m) to the newly identified high-pressure tetragonal phase (P4/nmm). Notably, NH₄F exhibits distinctive properties compared to its counterparts, resulting in a significantly broader pressure range over which this transition unfolds, facilitating the identification of its various stages. Our analysis points to a synergistic interplay driving the transition to the P4/nmm phase, which we name phase VIII. At intermediate pressures (around 40 GPa), a displacive transition of fluorine ions initiates a tetragonal distortion of the cubic phase. Subsequently, at higher pressures (around 115 GPa), every second ammonium ion undergoes a rotational shift, adopting an anti-tetrahedral arrangement. This coupled effect orchestrates the transition process, leading to the formation of the tetragonal phase. Solid ammonium fluoride has fascinating structural similarities with water ice, despite its ionic character. Here, the authors investigate NH4F at room temperature and high pressure, and report a new tetragonal phase formed through displacive transition of fluorine ions and subsequent rotation of ammonium ions in 'antiferromagnetic' units at ~115 GPa, which is unlike any form of ice. [ABSTRACT FROM AUTHOR]

2D semiconductors offer a promising pathway to replace silicon in next-generation electronics. Among their many advantages, 2D materials possess atomically-sharp surfaces and enable scaling the channel thickness down to the monolayer limit. However, these materials exhibit comparatively lower charge carrier mobility and higher contact resistance than 3D semiconductors, making it challenging to realize high-performance devices at scale. In this work, we search for high-mobility 2D materials by combining a high-throughput screening strategy with state-of-the-art calculations based on the ab initio Boltzmann transport equation. Our analysis singles out a known transition metal dichalcogenide, monolayer WS2, as the most promising 2D semiconductor, with the potential to reach ultra-high room-temperature hole mobilities in excess of 1300 cm2/Vs should Ohmic contacts and low defect densities be achieved. Our work also highlights the importance of performing full-blown ab initio transport calculations to achieve predictive accuracy, including spin–orbital couplings, quasiparticle corrections, dipole and quadrupole long-range electron–phonon interactions, as well as scattering by point defects and extended defects. [ABSTRACT FROM AUTHOR]

The advent of artificial intelligence (AI) has enabled a comprehensive exploration of materials for various applications. However, AI models often prioritize frequently encountered material examples in the scientific literature, limiting the selection of suitable candidates based on inherent physical and chemical attributes. To address this imbalance, we generated a dataset consisting of 1,453,493 natural language-material narratives from OQMD, Materials Project, JARVIS, and AFLOW2 databases based on ab initio calculation results that are more evenly distributed across the periodic table. The generated text narratives were then scored by both human experts and GPT-4, based on three rubrics: technical accuracy, language and structure, and relevance and depth of content, showing similar scores but with human-scored depth of content being the most lagging. The integration of multimodal data sources and large language models holds immense potential for AI frameworks to aid the exploration and discovery of solid-state materials for specific applications of interest. [ABSTRACT FROM AUTHOR]

Structural studies of pyrene have been limited to below 2 GPa. Here, we report on investigations of pyrene up to ~35 GPa using in situ single-crystal synchrotron X-ray diffraction in diamond anvil cells and ab initio calculations. They reveal the phase transitions from pyrene-I to pyrene-II (0.7 GPa), and to the previously unreported pyrene-IV (2.7 GPa), and pyrene-V (7.3 GPa). The structure and bonding analysis shows that gradual compression results in continuous compaction of molecular packing, eventually leading to curvature of molecules, which has never been observed before. Large organic molecules exhibit unexpectedly high conformational flexibility preserving pyrene-V up to 35 GPa. Ab initio calculations suggest that the phases we found are thermodynamically metastable compared to pyrene-III previously reported at 0.3 and 0.5 GPa. Our study contributes to the fundamental understanding of the polymorphism of polycyclic aromatic hydrocarbons and calls for further theoretical exploration of their structure–property relationships. Structural studies of pyrene, a polycyclic aromatic hydrocarbon, have so far been limited to below 2 GPa. Here, studying the crystal structure of pyrene up to ~35 GPa using in situ single-crystal synchrotron X-ray diffraction in diamond anvil cells, the authors discover two previously unobserved polymorphs, and find that gradual compression results in continuous compaction of molecular packing, eventually leading to a curvature of the molecules. [ABSTRACT FROM AUTHOR]

Lithiophilic modification of Li hosts is regarded as an effective strategy to address the uncontrollable Li dendrite issue for stably cycling lithium metal anode (LMA). Precise construction of stable and lightweight Li hosts with homogeneously distributed lithiophilic sites is vital to promoting uniform Li deposition but remains highly challenging, and the lithiophilic mechanism is still unrevealed. Herein, atomically dispersed single-, double-, and triple- Znn-anchored C2N matrixes (denoted as Znn@C2N, n = 1, 2, and 3) are proposed as potential lithiophilic hosts with well-defined and homogeneously distributed multilithiophilic sites to regulate Li metal deposition by means of DFT calculations and ab initio molecular dynamics simulations. The results demonstrate that Zn2 dimer-anchored C2N (Zn2@C2N) exhibits the highest thermodynamic stability and excellent electronic conductivity among the three atomically dispersed Znn single-atom/clusters anchored C2N hosts. The chemical essence of lithiophilic activity and the exact mechanism of Zn2@C2N as a promising Li host are systematically explored by in-depth analysis of the electron structure, local dipole, and chemical bonding at the atomical level. It is found that the lithiophilicity of Zn2@C2N is co-contributed by Zn2-anchoring and N-containing functional groups, which facilitate the uniform Li deposition by inducing heterogeneous nucleation at uniform and multiple lithiophilic sites. The moderate adsorption strength, low diffusion energy barrier, and stable atomic structure of these lithiophilic sites endow Zn2@C2N with low Li nucleation overpotential, smooth Li deposition morphology, and thus a long cycle life. This work sheds new light on the precise design of ideal lithiophilic hosts for dendrite-free LMA. [ABSTRACT FROM AUTHOR]

The efficient purification of cyclohexane is critical, serving as an essential feedstock to produce resins, nylon fibers and pharmaceutical intermediates. However, efficient purification remains a challenging task due to the similarity of cyclohexane and benzene molecules in terms of size and boiling point. In this work, we reported on the synergy of pore size and silanols inside an -SVR-type zeolite for the efficient production of ultrapure cyclohexane (benzene <1 ppm) from benzene/cyclohexane mixture. Under ambient conditions, the SSZ-74 zeolite demonstrated the highest mass-based productivity of 14.5 L/kg for ultrapure cyclohexane among several common zeolites with a considerable dynamic selectivity of ~9.5. The separation ability was evaluated through density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) simulations. The unique ordered silanols inside the zeolite frameworks demonstrated strong but reversible interactions with benzene through SiOH...π interactions, as revealed by in situ Fourier Transform infrared (FTIR) spectra. Purification of cyclohexane serves as a feedstock to produce resins, nylon fibers and pharmaceutical intermediates. Here authors combine specific pore sizes with silanols within a zeolite framework to improve the separation of cyclohexane from benzene, addressing the challenge of their molecular size similarity. [ABSTRACT FROM AUTHOR]

FeRh-based alloys have attracted significant attention due to their magnetic phase transition and significant magnetocaloric effects. These properties position them as promising candidates for fundamental research and practical applications, including magnetic cooling and targeted drug delivery. The study of FeRh alloys, particularly those where Rhodium or Iron atoms are substituted with other transition metals, is crucial as certain substitutions preserve the alloy's magnetocaloric properties. However, even within a specific structural type and without considering competing phases, determining which atom (Fe or Rh) is replaced upon introducing a third element remains unclear. This paper addresses this ambiguity through ab initio calculations. We propose an approach to predict whether a dopant will replace Fe or Rh, offering insights into the electronic and structural factors influencing the substitution. Additionally, we present a dataset of ab initio calculations on doped FeRh alloys, which will support future data-driven modeling efforts. Our findings not only advance the understanding of FeRh-based alloys but also contribute to the design of novel materials for experimental and industrial applications. [ABSTRACT FROM AUTHOR]

Larnite (β-Ca2SiO4) has previously been reported as an inclusion in sub-lithospheric diamonds and is generally interpreted as a retrograde reaction product of calcium silicate perovskite. In this study, we review the controls on the stability of the Ca2SiO4 polymorphs and show that phosphorus is likely essential for the preservation of β-Ca2SiO4. We also report a detailed study of the solubility of water and its incorporation mechanisms in γ-Ca2SiO4 and phosphorus-doped β-Ca2SiO4 using FTIR spectroscopy on high-pressure experiments quenched from 4–9.5 GPa and 1000–1200 °C combined with ab initio calculations. The experimentally determined water solubilities are in the range of 107–178 ppm. Our FTIR spectra and ab initio calculations indicate that for phosphorus-free γ-Ca2SiO4 the incorporation mechanism involves protonated Si and Ca1 vacancies. For phosphorus-bearing β-Ca2SiO4, our preferred incorporation mechanism involves one Si4+ ion replaced by one P5+ ion with a single protonated Ca2 vacancy. The low water solubility observed here for larnite implies that if primary calcium silicate perovskite inclusions trap high water concentrations during diamond growth from a volatile-rich fluid, measurements of the concentration of water in larnite will not provide a useful record of the initial volatile concentration. Instead, water would be hosted in other retrograde reaction products, possibly including exsolved fluids. [ABSTRACT FROM AUTHOR]

The physical properties of pure and defected ZnSe wurtzite systems were theoretically investigated. From the first-principle study, the wide band gap is 2.7 eV and ZnSe is a non-magnetic direct band-gap semiconductor. The ferromagnetic and antiferromagnetic states are also studied for Fe-doped ZnSe systems. Investigations show that adding iron and the presence of a single Zn vacancy defect leads to the magnetisation of ZnSe. The total energy calculations show that a ferromagnetic state is favourable when Zn is replaced with Fe. The ferromagnetic alignment in the Fe-doped ZnSe wurtzite compound allows it to be in high-spin and half-metallic states. In cases of Zn interstitial and Se vacancy defect in the ZnSe system does not lead to magnetisation. Defect formation energies and Curie temperature of Fe-doped ZnSe systems are estimated from ab-initio calculations. [ABSTRACT FROM AUTHOR]

Ab initio calculations based on density functional theory with the PBEsol method were utilized to examine the influence of hydrogen passivation, vacancies, and dopants on the electronic and magnetic properties of zigzag MgO nanoribbons with a width of w = 6 (6Z-MgONR). Calculations suggested that the 6Z-MgONR–2H configuration, which lacked magnetism and exhibited metallic characteristics, was the most stable configuration. Herein, this configuration with intrinsic defects and impurities were deeply considered. Finds revealed that individual VMg and VO vacancies induced magnetic moments of 0.624 μB and 0 μB, respectively. The calculated formation energy indicated that the occurrence of a single VMg was energetically favored than a single VO. Moreover, the three oxygen atoms adjacent to vacancy displayed inconsistent spin polarization directions, resulting in smaller magnetic moments than bulk MgO. Upon the introduction of Li or N impurities, LiMg under O-rich conditions exhibited the lowest formation energy. This was accompanied by an increase in total magnetic moments to 1.435 μB, which was significantly higher in the case of Mg vacancy. The corresponding spin-resolved charge density clearly demonstrated that the spin polarization was strongly localized at the right edge passivation of H atoms, with a minor contribution from the O atoms closest to the right edge H atoms. The NO/6Z-MgONR–2H configuration also exhibited total magnetic moments of 1.872 μB, but it had a substantially higher defect formation energy compared to the LiMg/6Z-MgONR–2H system. [ABSTRACT FROM AUTHOR]

The fine multiplet structure of the 1H NMR spectrum and the proton-coupled 15N NMR spectrum of indole was solved. A complete set of 1H–1H and 1H–15N coupling constants for [15N]indole in CD3CN solution was acquired with high accuracy. Ab initio quantum-chemical calculations of coupling constants with the DFT/B3LYP method showed a high level of agreement between the calculated and experimental values. The obtained data could serve as a reliable starting point for establishing the structure of new nitrogen-containing aromatic heterocycles. [ABSTRACT FROM AUTHOR]

The method of classical molecular dynamics with application of moment tensor potential of interatomic interaction were used to study diffusion properties of pure bcc β-Zr in the temperature range 1800–2100 K. The used potential was pre-trained on the data of ab initio calculations and verified by comparing the calculation results with the available experimental and theoretical data. The constructed potential reproduces the temperature phase transition from hcp α-Zr to bcc β-Zr, the experimental values of the thermal expansion coefficient and the diffusion coefficient, as well as the ab initio calculated equations of state of both phases at low temperatures. The dependence of the self-diffusion coefficient in zirconium on the strain in the range from –3 to 3% is obtained. It is shown that melting of the distorted structure can occur at a temperature below the melting temperature of the undeformed crystal. [ABSTRACT FROM AUTHOR]

Simulating electronic behavior in materials and devices with realistic large system sizes remains a formidable task within the ab initio framework due to its computational intensity. Here we show DeePTB, an efficient deep learning-based tight-binding approach with ab initio accuracy to address this issue. By training on structural data and corresponding ab initio eigenvalues, the DeePTB model can efficiently predict tight-binding Hamiltonians for unseen structures, enabling efficient simulations of large-size systems under external perturbations such as finite temperatures and strain. This capability is vital for semiconductor band gap engineering and materials design. When combined with molecular dynamics, DeePTB facilitates efficient and accurate finite-temperature simulations of both atomic and electronic behavior simultaneously. This is demonstrated by computing the temperature-dependent electronic properties of a gallium phosphide system with 106 atoms. The availability of DeePTB bridges the gap between accuracy and scalability in electronic simulations, potentially advancing materials science and related fields by enabling large-scale electronic structure calculations. Electronic simulations of large systems are computationally demanding. Here, authors develop DeePTB, a deep learning approach for efficient tight-binding calculations with ab initio accuracy, enabling million-atom simulations at finite temperatures. [ABSTRACT FROM AUTHOR]

The zinc boron complex formation was studied as a function of temperature (25, 50 and 70 °C) in boric acid solutions of various concentration (0.25, 0.50 and 0.68 mol·kg−1). pH was monitored during zinc ion addition by galvanostatic dissolution of a zinc metal electrode, in a solution of boric acid. The determination of the complex formation showed the importance of an accurate model of the polyborate speciation, recalculated for this work based on the previous literature data mainly potentiometric measurements completed by Raman spectroscopy and Ab Initio calculations. Modelling of our experimental results, considering various scenarios of boric acid speciation, was performed using R and PhreeqC, suggesting the formation of an aqueous triborate-zinc (II) complex, ZnB 3 O 3 (OH) 4 (aq) + , according to the reaction: Zn 2 + + 3 B (OH) 3 ⇌ ZnB 3 O 3 (OH) 4 (aq) + + 2 H 2 O + H + . The nature and structure of this aqueous complex disagrees with the results reported previously in the literature. Three formation constants of the triborate-zinc (II) complex were determined at 25, 50 and 70 °C as log 10 K ZnB = − 4.73 ± 0.10, − 4.21 ± 0.16 and − 4.94 ± 0.12, respectively. The evolution of zinc boron complex formation as a function of temperature (between 25 and 70 °C) provides information on the effect of the polyborate predominance in the solution on the complexation of zinc. [ABSTRACT FROM AUTHOR]

Context: One of the crucial issues related to machine learning potentials is the formation of representative dataset. For multicomponent systems, it is a general methodology to scan the composition range with a certain step. However, there is a lack of information on the compositional transferability of machine learning potentials. In this paper, we extend the knowledge in this area by studying the transferability of deep learning potential over the range of compositions of LiCl–KCl molten mixtures. The training dataset was formed using only the near-eutectic composition of 60% LiCl–40% KCl. Then, we tested the ability of the model to predict physicochemical properties of the melts far from the reference composition. It was found that for the composition range from 0 to 100% of LiCl, the calculated properties concur closely with those of other studies and ab initio calculations. Therefore, the model shows prominent non-intuitive compositional transferability. Moreover, the solid states and solid–liquid coexistence were reproduced. The calculated melting temperatures of LiCl and KCl show the errors of 6.6% and 0.4%, respectively. We argue that such good transferability stems from the local structure configurations that are typical both for pure LiCl and for pure KCl which are implicitly presented in the training dataset because of local fluctuations in composition. Methods: To collect the data for the initial dataset, density functional theory was employed. Then, the DeePMD package was used to train a neural network potential. To calculate the properties of the melts, standard equilibrium and non-equilibrium molecular dynamic approaches were utilized. [ABSTRACT FROM AUTHOR]

Context: We have computationally elucidated the mechanism for formation of H2O, N2O and CO3 from the reactions of CH2OO with H2, N2 and CO2, respectively, by the direct attack of the terminal O atom of CH2OO. This unique mechanism, which is characteristically "bee-sting-like" in nature, was found to be closely parallel to their reactions with the O(1D) atom. Reactions with H2 and CO2 take place by side-on attack, while the N2 reaction occurs by end-on attack with predicted barriers, 19.4, 13.1 and 25.3 kcal.mol−1, respectively. The CO2 reaction with CH2OO was found to occur by producing the C2v CO3, O = C < (O)O, instead of its D3h conformer, essentially similar to the O(1D) + CO2 reaction. The rate constants for the three reactions have been computed by the transition state theory (TST) based on the predicted potential energy profiles. We have also utilized the isodesmic nature of the dative bond exchange in the N2 reaction, CH2O → O + N2 = CH2O + N2 → O, to estimate the heat of the formation of CH2OO. Based on the heat of reaction computed at the highest level of theory employed, we obtained ΔfHo0 (CH2OO) = 27.5 kcal.mol−1; the value agrees with the recent results within ± 1 kcal.mol−1. Methods: All calculations were performed using Gaussian 16 software. Geometry, frequency, and IRC analysis calculations were conducted at the M06-2X/aug-cc-pVTZ level of theory. The heats of reaction have been evaluated at the highest level, CCSD(T)/CBS(T,Q,5)//M06-2x/aug-cc-pvTz. [ABSTRACT FROM AUTHOR]

Based on the ab initio scheme developed by the authors for calculating the asymptotic characteristics of decay channels of nuclear states—the method of orthogonal functions of cluster channels—an approach has been created that makes it possible to directly implement the results of ab initio calculations of -nucleon wave functions, as well as the partial decay widths of resonant states of compound nucleus obtained through their use, into calculations of cross sections for resonance nuclear reactions. Both calculated and reliably measured resonance energies can be employed in these calculations. Using the examples of such a theoretical analysis of the reaction cross sections for He and He, the efficiency of this approach and the wide prospects of its use in nuclear spectroscopy are demonstrated. [ABSTRACT FROM AUTHOR]

Single-isotherm n(p, T90) results are reported for the gases Ar, N2, H2O, and D2O at vacuum wavelength λ = 1542.383 (1) nm. The argon and nitrogen isotherms were measured near 303 K; the water isotherms were measured near 373 K. Combined with the two previous articles of this series, the present results beget several insights via dispersion analyses. The argon result is highly consistent with static measurement plus ab initio calculation of dispersion polarizability. The nitrogen result is nominally consistent with one recent experiment and the dipole oscillator strength distributions, but the present work offers a refined estimate of the molar refractivity at optical wavelengths. For ordinary and heavy water, the dispersion trend is nominally consistent with existing liquid measurements. However, water's absorption features in the near-infrared preclude a reliable comparison of the present result with literature. [ABSTRACT FROM AUTHOR]

Context: We have computationally elucidated the mechanism for formation of H2O, N2O and CO3 from the reactions of CH2OO with H2, N2 and CO2, respectively, by the direct attack of the terminal O atom of CH2OO. This unique mechanism, which is characteristically "bee-sting-like" in nature, was found to be closely parallel to their reactions with the O(1D) atom. Reactions with H2 and CO2 take place by side-on attack, while the N2 reaction occurs by end-on attack with predicted barriers, 19.4, 13.1 and 25.3 kcal.mol−1, respectively. The CO2 reaction with CH2OO was found to occur by producing the C2v CO3, O = C < (O)O, instead of its D3h conformer, essentially similar to the O(1D) + CO2 reaction. The rate constants for the three reactions have been computed by the transition state theory (TST) based on the predicted potential energy profiles. We have also utilized the isodesmic nature of the dative bond exchange in the N2 reaction, CH2O → O + N2 = CH2O + N2 → O, to estimate the heat of the formation of CH2OO. Based on the heat of reaction computed at the highest level of theory employed, we obtained ΔfHo0 (CH2OO) = 27.5 kcal.mol−1; the value agrees with the recent results within ± 1 kcal.mol−1. Methods: All calculations were performed using Gaussian 16 software. Geometry, frequency, and IRC analysis calculations were conducted at the M06-2X/aug-cc-pVTZ level of theory. The heats of reaction have been evaluated at the highest level, CCSD(T)/CBS(T,Q,5)//M06-2x/aug-cc-pvTz. [ABSTRACT FROM AUTHOR]

Aliphatics prevail in asteroids, comets, meteorites and other bodies in our solar system. They are also found in the interstellar and circumstellar media both in gas-phase and in dust grains. Among aliphatics, linear alkanes (n-CnH2n+2) are known to survive in carbonaceous chondrites in hundreds to thousands of parts per billion, encompassing sequences from CH4 to n-C31H64. Despite being systematically detected, the mechanism responsible for their formation in meteorites has yet to be identified. Based on advanced laboratory astrochemistry simulations, we propose a gas-phase synthesis mechanism for n-alkanes starting from carbon and hydrogen under conditions of temperature and pressure that mimic those found in carbon-rich circumstellar envelopes. We characterize the analogs generated in a customized sputter gas aggregation source using a combination of atomically precise scanning tunneling microscopy, non-contact atomic force microscopy and ex-situ gas chromatography-mass spectrometry. Within the formed carbon nanostructures, we identify the presence of n-alkanes with sizes ranging from n-C8H18 to n-C32H66. Ab-initio calculations of formation free energies, kinetic barriers, and kinetic chemical network modelling lead us to propose a gas-phase growth mechanism for the formation of large n-alkanes based on methyl-methylene addition (MMA). In this process, methylene serves as both a reagent and a catalyst for carbon chain growth. Our study provides evidence of an aliphatic gas-phase synthesis mechanism around evolved stars and provides a potential explanation for its presence in interstellar dust and meteorites. Extraterrestrial organic matter found in meteorites may hold a unique record of its synthesis, and chemical and thermal alterations in the parent body, however, the origin of such aliphatics remains enigmatic. Here, the authors propose sequential gas-phase methyl-methylene addition growth of n-C8H18 to n-C32H66 alkanes based on a series of sputter gas aggregation source experiments and DFT calculations. [ABSTRACT FROM AUTHOR]

The calculation of electron density distribution using density functional theory (DFT) in materials and molecules is central to the study of their quantum and macro-scale properties, yet accurate and efficient calculation remains a long-standing challenge. We introduce ChargE3Net, an E(3)-equivariant graph neural network for predicting electron density in atomic systems. ChargE3Net enables the learning of higher-order equivariant features to achieve high predictive accuracy and model expressivity. We show that ChargE3Net exceeds the performance of prior work on diverse sets of molecules and materials. When trained on the massive dataset of over 100K materials in the Materials Project database, our model is able to capture the complexity and variability in the data, leading to a significant 26.7% reduction in self-consistent iterations when used to initialize DFT calculations on unseen materials. Furthermore, we show that non-self-consistent DFT calculations using our predicted charge densities yield near-DFT performance on electronic and thermodynamic property prediction at a fraction of the computational cost. Further analysis attributes the greater predictive accuracy to improved modeling of systems with high angular variations. These results illuminate a pathway towards a machine learning-accelerated ab initio calculations for materials discovery. [ABSTRACT FROM AUTHOR]

Current research is in constant evolution, regularly revealing surprises that challenge our current understanding. Introducing magnetism into non-magnetic materials like ZnO is motivated by the desire to create new properties and develop innovative technological applications. In this work, magnetization is generated in O-polar ZnO by implanting krypton ions. Krypton is chemically unreactive and does not engage in chemical bonding within the compound; magnetization results from the radiation damage caused by the implantation process. The Kr implantation increases the lattice parameters and defect density. Large magnetization values of approximately 186 emu cm−3 were observed upon implantation. To discern the mechanism leading to the induced magnetism, we have performed ab initio calculations. We modeled the effects caused by beam damage by simulating mechanical constraints and introducing Zn and O vacancies. The calculations clearly show that the magnetism in pristine ZnO was attributed to Zn vacancies, where a magnetic moment of around 2µB was observed. Oxygen defects lead to negligible magnetization within the cell (10−5 µB). The effects of strain on the observed magnetism were also negligible. The introduction of Zn vacancies in the ZnO matrix leads to localized unpaired electrons, creating large local magnetic moments. This disruption of the electronic structure results in an asymmetry between spin-up and spin-down states, promoting magnetic alignment. Interaction between these magnetic moments near the vacancies establishes a pronounced magnetic region with a reduced charge density, while the regions far away from the vacancy were found to be non-magnetic with a higher charge density, shedding light on the induced magnetism in the material. Our research is of crucial importance in shedding light on the fundamental mechanisms of magnetism induced in ZnO. [ABSTRACT FROM AUTHOR]