Search

We analyze the adsorption and ring‐opening reaction of pentacyclic chalcogen alkyls with chalcogen atoms ranging from oxygen to tellurium using computational analysis. Thus extends our previous investigation of THF on silicon towards germanium surface and towards the heavier chalcogen homologues. We found an increasing dative bond strength of the precursor state with the period of the chalcogen atom on both surfaces. Using energy decomposition analysis for extended systems (pEDA), differences in the trends between silicon and germanium were revealed. Following the dative bound state, subsequent ring‐opening reactions were found to proceed via a nucleophilic back‐side attack, similar to a molecular SN2 reaction. Reaction energies and barrier heights show a maximum for the sulfur derivative. This trend was found to correlate with the position of the transition state in the reaction and agrees with the molecular reactivity. The uniquely low barrier of THF can be attributed to its ring strain. Our findings shed light on the fundamental aspects of surface chemistry and the benefits of using quantitative bonding analysis in this field. It also paves the way for future explorations into the functionalization of semiconductor surfaces using higher‐period ether derivatives. [ABSTRACT FROM AUTHOR]

A computational methodology, founded on chemical concepts, is presented for interpreting the role of nuclear motion in the electron transport through single‐molecule junctions (SMJ) using many‐electron ab initio quantum chemical calculations. Within this approach the many‐electron states of the system, computed at the SOS‐ADC(2) level, are followed along the individual normal modes of the encapsulated molecules. The inspection of the changes in the partial charge distribution of the many‐electron states allows the quantification of the electron transport and the estimation of transmission probabilities. This analysis improves the understanding of the relationship between internal motions and electron transport. Two SMJ model systems are studied for validation purposes, constructed from a conductor (BDA, benzene‐1,4‐diamine) and an insulator molecule (DABCO, 1,4‐diazabicyclo[2.2.2]octane). The trends of the resulting transmission probabilities are in agreement with the experimental observations, demonstrating the capability of the approach to distinguish between conductor and insulator type systems, thereby offering a straightforward and cost‐effective tool for such classifications via quantum chemical calculations. [ABSTRACT FROM AUTHOR]

By using ab initio simulations based on density functional theory and many‐body perturbation theory, a comprehensive analysis of the distinct optical signatures of various tellurene polymorphs and their associated unique anisotropic excitonic characteristics is presented. Despite the atomic thickness of these materials, these findings reveal that their optical absorbance reaches as high as 50% in the near‐infrared and visible range. This investigation highlights the exceptional potential of these 2D semiconducting materials in the development of ultra‐thin and flexible homo‐ and hetero‐junctions for solar light harvesting, achieving photoconversion efficiencies up to 19%, a performance level comparable to current silicon technologies. [ABSTRACT FROM AUTHOR]

Thin films of crystalline solids with substantial free volume built from organic chromophores and metal secondary building units (SBUs) are promising for engineering new optoelectronic properties through control of interchromophore coupling. Zn‐based SBUs are especially relevant in this case because they avoid quenching the chromophore's luminescence. We find that layer‐by‐layer spin‐coating using Zn acetate dihydrate and benzene‐1,4‐dicarboxylic acid (H2BDC) and biphenyl‐4,4'‐dicarboxylic acid (H2BPDC) linkers readily produces crystalline thin films. However, analysis of the grazing‐incidence wide‐angle X‐ray scattering (GIWAXS) data reveals the structures of these films vary significantly with the linker, and with the metal‐to‐linker molar ratio used for fabrication. Under equimolar conditions, H2BPDC creates a type of structure like that proposed for SURMOF‐2, whereas H2BDC generates a different metal‐hydroxide‐organic framework. Large excess of Zn2+ ions causes the growth of layered zinc hydroxides, irrespective of the linker used. Density functional theory (DFT) calculations provide structural models with minimum total energy that are consistent with the experimentally observed diffractograms. In the broader sense, this work illustrates the importance in this field of careful structure determination, e. g., by utilizing GIWAXS and DFT simulations to determine the structure of the obtained crystalline metal‐organic thin films, such that properties can be rationally engineered and explained. [ABSTRACT FROM AUTHOR]

The work function is the key surface property that determines the energy required to extract an electron from the surface of a material. This property is crucial for thermionic energy conversion, band alignment in heterostructures, and electron emission devices. This work presents a high‐throughput workflow using density functional theory (DFT) to calculate the work function and cleavage energy of 33,631 slabs (58,332 work functions) that are created from 3,716 bulk materials. The number of calculated surface properties surpasses the previously largest database by a factor of ≈27. Several surfaces with an ultra‐low (<2 eV) and ultra‐high (>7 eV) work function are identified. Specifically, the (100)‐Ba‐O surface of BaMoO3 and the (001)‐F surface of Ag2F have record‐low (1.25 eV) and record‐high (9.06 eV) steady‐state work functions. Based on this database a physics‐based approach to featurize surfaces is utilized to predict the work function. The random forest model achieves a test mean absolute error (MAE) of 0.09 eV, comparable to the accuracy of DFT. This surrogate model enables rapid predictions of the work function (≈ 105 faster than DFT) across a vast chemical space and facilitates the discovery of material surfaces with extreme work functions for energy conversion and electronic device applications. [ABSTRACT FROM AUTHOR]

Flavonoids are natural products commonly found in the human diet with anti‐viral activity. The electrochemical activity of flavonoids is effective in their inhibitory properties. Herbacetin is an anti‐coronavirus drug from the flavonoid family. To understand structure‐electrochemical activity relations, ab initio calculations on some selected herbacetin derivatives were carried out using Gaussian 09 in B3LYP/6‐311G*. The effect of the position and type of the various substituents in the ring A of the flavone backbone are considered. The oxygen charge density of the hydroxyl group on C8 (O8) in the considered herbacetins was compared using nuclear quadrupole coupling constants (NQCC) calculations. Results showed that the presence of the amino group in the ortho position of O8 has the most significant effect on increasing the charge density of the O8 atom (O8‐NQCC=9.23 MHz). Based on the proposed mechanism of these drugs, ortho‐amino herbacetin is expected to show a significant anti‐coronavirus effect. Comparison of calculated O8‐NQCCs of tangeretin and nobiletin with herbacetin shows that with the replacement of OH with OCH3, the charge density of oxygen atoms decreases (about 2 MHz). Therefore tangeretin and nobiletin have a lower drug effect than herbacetin. Natural bond orbital (NBO) results are in agreement with calculated NQCCs. [ABSTRACT FROM AUTHOR]

Layered halide perovskites are solution‐processed natural heterostructures where quantum and dielectric confinement down to the nanoscale strongly influence the optical properties, leading to stabilization of bound excitons. Detailed understanding of the exciton properties is crucial to boost the exploitation of these materials in energy conversion and light emission applications, with on‐going debate related to the energy order of the four components of the most stable exciton. To provide theoretical feedback and solve among contrasting literature reports, this work performs ab initio solution of the Bethe–Salpeter equation (BSE) for symmetrized reference Cs2PbX4 (X = I and Br) models, with detailed interpretation of the spectroscopic observables based on group‐theory analysis. Simulations predict the following Edark < Ein‐plane < Eout‐of‐plane fine‐structure assignment, consistent with recent magneto‐absorption experiments and obtain similar increase in dark/bright splitting when going from lead‐iodide to a lead‐bromide composition as found experimentally. The authors further suggest that polar distortions may lead to stabilization of the in‐plane component and end‐up in a bright lowest exciton component, discuss exciton landscape over a broad energy range and clarify the exciton spin‐character, when large spin‐orbit coupling is in play, to rationalize the potential of halide perovskites as triplet sensitizers in combination with organic dyes. [ABSTRACT FROM AUTHOR]

Molecular quantum‐dot cellular automata (QCA) is a low‐power computing paradigm that may offer ultra‐high device densities and THz‐speed switching at room temperature. A single mixed‐valence (MV) molecule acts as an elementary QCA device known as a cell. Cells coupled locally via the electrostatic field form logic circuits. However, previously‐synthesized ionic MV molecular cells are affected by randomly‐located, nearby neutralizing counterions that can bias device states or change device characteristics, causing incorrect computational results. This ab initio study explores how non‐biasing counterions affect individual molecular cells. Additionally, we model two novel neutral, zwitterionic MV QCA molecules designed to avoid biasing and other undesirable counterionic effects. The location of the neutralizing counterion is controlled by integrating one counterion into each cell at a well‐defined, non‐biasing location. Each zwitterionic QCA candidate molecule presented here has a fixed, integrated counterion, which neutralizes the mobile charges used to encode the device state. [ABSTRACT FROM AUTHOR]

X-ray and electron scattering from free gas-phase molecules is examined using the independent atom model (IAM) and ab initio electronic structure calculations. The IAM describes the effect of the molecular geometry on the scattering, but does not account for the redistribution of valence electrons due to, for instance, chemical bonding. By examining the total, i.e. energy-integrated, scattering from three molecules, fluoroform (CHF3), 1,3-cyclohexadiene (C6H8) and naphthalene (C10H8), the effect of electron redistribution is found to predominantly reside at small-to-medium values of the momentum transfer (q ≤ 8 Å-1) in the scattering signal, with a maximum percent difference contribution at 2 ≤ q ≤ 3 Å-1. A procedure to determine the molecular geometry from the large-q scattering is demonstrated, making it possible to more clearly identify the deviation of the scattering from the IAM approximation at small and intermediate q and to provide a measure of the effect of valence electronic structure on the scattering signal. [ABSTRACT FROM AUTHOR]

Acute Hepatopancreatic Necrosis Disease (AHPND) represents a significant challenge in the field of shrimp aquaculture. This disease is primarily caused by Vibrio parahaemolyticus strains harbouring the pVA1 plasmid encoding the PirAvp and PirBvp toxins. To combat this epidemic and mitigate its devastating consequences, it is crucial to identify and characterize the receptors responsible for the binding of these pathogenic toxins. Our studied discovered that Penaeus vannamei's Serine protease inhibitor 3 (PvSerpin3) derived from shrimp hepatopancreatic tissues could bind to recombinant PirAvp, confirming its role as a novel PirAvp‐binding protein (PABP). Through comprehensive computational methods, we revealed two truncated PirAvp–binding proteins derived from PvSerpin3 called Serpin3(13) and Serpin3(22), which had higher affinity to PirAvp than the full‐length PvSerpin3. The PABP genes were amplified from a cDNA library that was reversed from total RNA extracted from shrimp, cloned and expressed in Escherichia coli. Three PABP inclusion bodies were refolded to obtain the soluble form, and the recovery efficacy was found to be 100% for Serpin3 and Serpin3(13), while Serpin3(22) had a recovery efficacy of roundly 50%. Co‐Immunoprecipitation (co‐IP) and dot blot assays substantiated the interaction of these recombinant PABPs with both recombinant PirAvp and VPAHPND (XN89)‐producing natural toxins. [ABSTRACT FROM AUTHOR]

In this work, we report rovibrational energy levels for four isotopologues of methylene (CH2, CHD, CD2, and 13CH2) in their ground triplet electronic state (X~3B1) from variational calculation up to ~10,000 cm−1 and using a new accurate ab initio potential energy surface (PES). Triplet methylene exhibits a large‐amplitude bending vibration and can reach a quasilinear configuration due to its low barrier (~2000 cm−1). To construct the ab initio PES, the Dunning's augmented correlation‐consistent core‐valence orbital basis sets were employed up to the sextuple‐ζ quality [aug‐cc‐pCVXZ, X = T, Q, 5, and 6] combined with the single‐ and double‐excitation unrestricted coupled cluster approach with a perturbative treatment of triple excitations [RHF‐UCCSD(T)]. We have shown that the accuracy of the ab initio energies is further improved by including the corrections due to the scalar relativistic effects, DBOC and high‐order electronic correlations. For the first time, all the available experimental rovibrational transitions were reproduced with errors less than 0.12 cm−1, without any empirical corrections. Unlike more "traditional" nonlinear triatomic molecules, we have shown that even the energies of the ground vibrational state (000) with rather small rotational quantum numbers are strongly affected by the very pronounced rovibrational resonance interactions. Accordingly, the polyad structure of the vibrational levels of CH2 and CD2 was analyzed and discussed. The comparison between the energy levels obtained from the effective Watson A‐reduced Hamiltonian, from the generating‐function approach and from a variational calculation was given. [ABSTRACT FROM AUTHOR]

Recent research suggests that photocatalytic activity toward water splitting of strontium titanate SrTiO3 (STO) is enhanced by creating multifaceted nanoparticles. To better understand the source of this activity, a previously designed model is used for two types of surfaces of this nanoparticle, flat and double‐stepped. Density functional theory calculations of water adsorption on these surfaces are performed to gain insight into water adsorption and proton migration processes, as well as thermodynamics of hydrogen evolution reaction within the framework of computational hydrogen electrode. It is concluded that ridges of single‐ and double‐stepped surfaces are nearly identical in terms of adsorption configurations and energetics. Also, it is demonstrated that protons have migration barriers lower than 0.7 eV and that surface morphology impacts catalytic activity toward hydrogen evolution reaction, with flat surface demonstrating higher catalytic activity. [ABSTRACT FROM AUTHOR]

Recent research suggests that photocatalytic activity toward water splitting of strontium titanate SrTiO3 (STO) is enhanced by creating multifaceted nanoparticles. To better understand the source of this activity, a previously designed model is used for two types of surfaces of this nanoparticle, flat and double‐stepped. Density functional theory calculations of water adsorption on these surfaces are performed to gain insight into water adsorption and proton migration processes, as well as thermodynamics of hydrogen evolution reaction within the framework of computational hydrogen electrode. It is concluded that ridges of single‐ and double‐stepped surfaces are nearly identical in terms of adsorption configurations and energetics. Also, it is demonstrated that protons have migration barriers lower than 0.7 eV and that surface morphology impacts catalytic activity toward hydrogen evolution reaction, with flat surface demonstrating higher catalytic activity. [ABSTRACT FROM AUTHOR]

The geometries of nitromethane‐carbonyl dimers were investigated comprehensively with formaldehyde, acetaldehyde and acetone as model Lewis bases. Pnicogen bonding involving nitrogen of nitromethane was discerned to be a stabilizing interaction along with hydrogen and tetrel (carbon) bonding interactions in all these dimers. The structures of the dimers generated at low temperatures under isolated conditions were established using infrared spectroscopy with the aid of ab initio and DFT computations. The existence of C−H⋅⋅⋅O hydrogen, O=N⋅⋅⋅O, O=N⋅⋅⋅π pnicogen and O=C⋅⋅⋅O tetrel bonding was asserted from Quantum Theory of Atoms In Molecules (QTAIM), Natural Bond Orbital (NBO), Electrostatic Potential (ESP) mapping and Non‐Covalent Interaction (NCI) analyses. Methyl substitution on formaldehyde results in the instigation of steric effect which was found to have a profound influence on the geometries of heterodimers of nitromethane‐acetaldehyde and nitromethane‐acetone. The plausible role of steric effect on pnicogen and tetrel bonding was probed through the analysis of nature of interactions in these nitromethane‐carbonyl dimer systems. [ABSTRACT FROM AUTHOR]

Argon compounds play an important role in the mass spectrometry with inductively coupled plasma and other applications. At the same time, there is a little knowledge of their electronic terms and thermodynamic functions due to the complexity of experimental observations. In this work, the ab initio simulations are performed to obtain the interatomic interaction potentials for the ground and excited states of ArN and ArN+. Using these potentials, the vibrational‐rotational partition functions and thermodynamic properties in the gas phase are calculated for these molecules at the temperature range of 298.15–10,000 K. The errors of the thermodynamic functions associated with the approximation of interatomic interaction potentials are estimated. [ABSTRACT FROM AUTHOR]

Argon compounds play an important role in the mass spectrometry with inductively coupled plasma and other applications. At the same time, there is a little knowledge of their electronic terms and thermodynamic functions due to the complexity of experimental observations. In this work, the ab initio simulations are performed to obtain the interatomic interaction potentials for the ground and excited states of ArN and ArN+. Using these potentials, the vibrational‐rotational partition functions and thermodynamic properties in the gas phase are calculated for these molecules at the temperature range of 298.15–10,000 K. The errors of the thermodynamic functions associated with the approximation of interatomic interaction potentials are estimated. [ABSTRACT FROM AUTHOR]

The nitrogen of nitro group is a paradigmatic pnictogen due the presence of a π‐hole and a number of studies have been performed recently on prototypical nitromethane (NM). Homodimers and heterodimers of NM are sustained by π‐hole driven pnictogen bonds hosted by nitrogen. To understand the effect of substitution on this π‐hole and thus the pnictogen bond, heterodimers of nitrobenzene (NB; phenyl substitution in place of methyl) with ammonia (AM) have been probed, as a test case, using matrix isolation infrared spectroscopy and ab initio computations. Of the four structures optimized on the potential energy surface the energetically dominant global minimum, stabilized by π‐hole driven O=N←N pnictogen bonding with co‐operative N−H←O hydrogen bonding, was experimentally identified at low temperatures. A comparison of the pnictogen bonding of NB‐AM dimers with NM counterpart (NM‐AM dimers) divulged the dominance of electrostatic origin of pnictogen bonding in both the class of dimers. The reduced strength of pnictogen bonding in NB‐AM dimers in comparison to NM‐AM dimers was discerned, which has been established to be a consequence of the reduced electrostatic potential at the π‐hole of NB relative to that in NM. The strength of π‐hole driven pnictogen bond was directly correlated with the binding energy and the infrared shifts in the signature vibrational bands of the NB, NM and AM submolecules due to dimerization under matrix isolated conditions at low temperatures. [ABSTRACT FROM AUTHOR]

Herein, the mechanisms for radiation resistance of InP are investigated using first‐principle computational methods. It is found that the substantial recovery of post‐irradiated solar cells is attributed to the minority‐carrier‐injection‐enhanced annealing of the negative‐U defects, phosphorus vacancies, which produce the (0/−) and (+/0) level corresponding to the deep‐level transient spectroscopy signature H4 and E11, respectively. P vacancies can annihilate with P interstitials at low temperature, where by alternately capturing carrier with opposite sign P, interstitials become highly mobile upon minority‐carrier injection. By such Bourgoin diffusion mechanism, the calculated barrier for P interstitial migration and P Frenkel pair recombination are lowered to 0.04 and 0.16 eV, respectively. The results agree fairy well with experimental observations. [ABSTRACT FROM AUTHOR]

Fanpy is a free and open‐source Python library for developing and testing multideterminant wavefunctions and related ab initio methods in electronic structure theory. The main use of Fanpy is to quickly prototype new methods by making it easier to convert the mathematical formulation of a new wavefunction ansätze to a working implementation. Fanpy is designed based on our recently introduced Flexible Ansatz for N‐electron Configuration Interaction (FANCI) framework, where multideterminant wavefunctions are represented by their overlaps with Slater determinants of orthonormal spin‐orbitals. In the simplest case, a new wavefunction ansatz can be implemented by simply writing a function for evaluating its overlap with an arbitrary Slater determinant. Fanpy is modular in both implementation and theory: the wavefunction model, the system's Hamiltonian, and the choice of objective function are all independent modules. This modular structure makes it easy for users to mix and match different methods and for developers to quickly explore new ideas. Fanpy is written purely in Python with standard dependencies, making it accessible for various operating systems. In addition, it adheres to principles of modern software development, including comprehensive documentation, extensive testing, quality assurance, and continuous integration and delivery protocols. This article is considered to be the official release notes for the Fanpy library. [ABSTRACT FROM AUTHOR]

Quantum‐mechanical‐based computational design of molecular catalysts requires accurate and fast electronic structure calculations to determine and predict properties of transition‐metal complexes. For Zr‐based molecular complexes related to polyethylene catalysis, previous evaluation of density functional theory (DFT) and wavefunction methods only examined oxides and halides or select reaction barrier heights. In this work, we evaluate the performance of DFT against experimental redox potentials and bond dissociation enthalpies (BDEs) for zirconocene complexes directly relevant to ethylene polymerization catalysis. We also examined the ability of DFT to compute the fourth atomic ionization potential of zirconium and the effect the basis set selection has on the ionization potential computed with CCSD(T). Generally, the atomic ionization potential and redox potentials are very well reproduced by DFT, but we discovered relatively large deviations of DFT‐calculated BDEs compared to experiment. However, evaluation of BDEs with CCSD(T) suggests that experimental values should be revisited, and our CCSD(T) values should be taken as most accurate. [ABSTRACT FROM AUTHOR]

Several properties of a series of novel disubstituted pentacenes, in which the substituents are donor and acceptor groups, were investigated by using the ab initio methods. In particular, the role of different substitution positions for acceptor group was explored. Calculations predict that pentacene derivatives were highly soluble and oxidatively stable than the unsubstituted pentacene. Simulated absorption spectra show that 9‐nitropentacen‐2‐amine (PD2) exhibits three absorption bands in the ultraviolet and visible regions. In general, substituents have important impact on the first hyperpolarizability value, and a remarkable enhancement of static second hyperpolarizability is revealed in this study; however, further investigations are required to confirm this finding. Molecular dynamics simulations of the solid state suggest that a material based on 9‐nitropentacen‐2‐amine and 10‐nitropentacen‐2‐amine could exhibit low resistivity due to the potential amount of π–π stacking. The results emphasize the potential of using the herein studied pentacene‐based compounds, with particular reference to PD2, for future applications in the optoelectronic and photonic fields. [ABSTRACT FROM AUTHOR]

This study has used ab initio technique to investigate the electro‐optical and electronic properties of N‐(4‐methoxybenzylidene)‐4‐butylaniline (MBBA), a nematic liquid crystal between 21 and 48 °C, surrounded by gas and acetonitrile medium, in the presence and absence of electric field. The optimization and analysis of various electro‐optical and electronic parameters along with absorption spectrum have been performed using ωB97xD/6‐311+G(d,p) and M062X/6‐311+G(d,p) methods. Under the electric field, electro‐optical parameters of MBBA surrounded by acetonitrile are increased, indicating its suitability for display device development application. Global reactivity descriptors reveal that electronic properties of the MBBA LC also high in acetonitrile medium as compared to that of the gas. Furthermore, using second order perturbation theory and the multicentered‐multipole expansion technique, the mutual interactions between a pair of MBBA molecules are examined, revealing the nematic behavior of MBBA molecule. [ABSTRACT FROM AUTHOR]

Aluminum nitride (AlN) and boron nitride (BN) are well‐known ceramic materials with numerous valuable properties, whereas recently there is a growing field of research on the AlN/BN advanced ceramic materials. Here, we present a study on boron‐rich AlN, structural and electronic properties, and structure–property relationship. Several AlxB1−xN solid solutions (x = 1,.875,.75, and.625) have been investigated, and structure optimization has been performed for four different structure types: h‐BN, wurtzite, sphalerite, and rock salt. First‐principles calculations were performed using hybrid B3LYP functional. New modifications and compounds have been predicted as a function of boron concentration in AlN, and especially, interesting phase transitions were found at extreme pressure conditions. Electronic properties and band structures were computed, and the possibility for bandgap tuning has been discovered. The present study, and especially the structure–property relationship, gives new possibilities for bandgap engineering in boron‐rich AlN electroceramic materials. [ABSTRACT FROM AUTHOR]

Earth's core has produced a global magnetic field for at least the last 3.5 Gyrs, presently sustained by inner core (IC) growth. Models of the core with high thermal conductivity suggest potentially insufficient power available for the geodynamo prior to IC formation ∼1 Ga. Precipitation of silicon from the liquid core might offer an alternative power source for the ancient magnetic field, although few estimates of the silicon partition coefficient exist for conditions of the early core. We present the first ab initio determination of the silicon partition coefficient at core‐mantle boundary conditions and use these results to confirm a thermodynamic description of partitioning that is integrated into a model of coupled core‐mantle thermal evolution. We show that models including precipitation of silicon can satisfy constraints of IC size, mantle convective heat flux, mantle temperature and a persistent ancient geodynamo, and favor an oxygen poor initial core composition. Plain Language Summary: The iron core at the center of the Earth presently has a molten outer shell and solid inner region which is growing as the Earth cools. This inner core (IC) growth provides power to the outer core (OC) because elements excluded from the IC are light and rise to the top of the OC. Today, this power drives the Earth's magnetic field but was not available before the IC began to freeze 1 billion years ago. Despite this, the rock record shows that the magnetic field has been extant for 4 billion years, raising the question of how it was powered before the IC formed. Here, we perform calculations of the constituent liquid iron alloys in the core to understand the conditions which allow silicon to be dissolved into the core. We find that for a low oxygen condition, silicon can be dissolved into the hot ancient core and then released as the Earth cools, leaving behind dense, iron rich liquids which sink providing an alternate source of convective power. We show that this process could have powered the magnetic field before the IC formed and might constrain the core composition. Key Points: First ab initio calculations of silicon partitioning (PT) at core mantle boundary conditionsNew partition coefficients are consistent with a large data set of experimental PT resultsPowering the ancient geodynamo with silicon precipitation in a high thermal conductivity core may place constraint on core composition [ABSTRACT FROM AUTHOR]

So far, numerous researches on the He2H− system have still been restricted to several analytical forms of the potential energy interaction, where the calculations in the three‐body interaction may be not precise. With that in mind, we have provided an accurate, global, full‐dimensional potential energy surface (PES) for the ground state of the He2H− system by the fundamental invariant neural network (FI‐NN) fitting based on roughly 45 000 ab initio data points. The energy points are calculated with the coupled‐cluster singles and doubles with perturbative triples (CCSD[T]) method using the augmented Dunning‐type correlation‐consistent (aug‐cc‐pVTZ, aug‐cc‐pVQZ and aug‐cc‐pV5Z) basis sets, respectively. Based on adoption and comparison of three different extrapolation formulas, we obtained even accurate data points, which are extrapolated to the complete basis set (CBS) limit. The overall root mean square error of the fitting PES is only about 6.314 × 10−3 cm−1. It can be expected that this accurate PES would provide insights to further interesting discoveries in dynamics or spectroscopies for the relevant molecular systems. [ABSTRACT FROM AUTHOR]

Transformation‐induced plasticity (TRIP) steels from the third generation of advanced high‐strength steels (AHSS) contain Si additions to prevent the formation of carbides. Cementite (Fe3C) is a prototype among the carbides, and despite the importance of the influence of alloying elements on its stability, mechanisms by which the elements act have not been clarified so far. Herein, ab initio calculations are employed to study the impact of several alloying elements, including Al, Cr, Mg, Mn, and Si, on the stability of cementite. Partitioning energies are calculated to determine the segregation tendency of alloying elements between the phases such as ferrite, austenite, and cementite. The change in formation energy between the alloyed cementite and the pure cementite is then used to quantify the phase (de)stabilization. Therefore, both the partitioning energy and the change in formation energy must be considered together in a multiphase alloy system to make statements about the effect of alloying elements on the cementite stability are proposed. In addition, the effects of the technically most important elements Al and Si on the mechanical properties of cementite are calculated using the stress–strain method. Both the elements are found to increase the elastic stability of cementite. [ABSTRACT FROM AUTHOR]

Through the comprehensive analysis of ab initio and experimental results of a large number of diatomic systems, the systematic deviation of ab initio method in vibrational energies prediction caused by physical/mathematical simplification is located. A joint ab initio and machine learning method based on information across molecules is proposed to deal with the problem. Starting from an ab initio model, and then systematically modifying it through machine learning, the vibrational energies prediction of many diatomic systems (SiC, HBr, NO, PC, N2, SiO, O2, ClF, etc.) have been improved, and significantly surpassed the more complex ab initio model. In addition to the improvement of accuracy, the new method also greatly reduces the computational expense, and is applicable for the systems without experimental data. [ABSTRACT FROM AUTHOR]

Three heterometallic hexanuclear 3d–4f complexes bearing the formula [Cu2(L)2Ln4(L)4(o‐van)2] [L=2‐((E)‐((2‐hydroxyphenyl)imino]methyl)phenol; o‐van=ortho‐vanillin] (LnIII=GdIII (1), DyIII (2), and TbIII (3)) have been synthesized and characterized. DC magnetic susceptibility measurements reveal overall antiferromagnetic interactions in 1 and 3, whereas co‐existence of ferro‐ as well as antiferromagnetic interactions were observed in 2. The magnetocaloric effect has been observed for 1 with an entropy change (−ΔSm) of 22.3 J kg−1 K−1 at 3 K and 7 T. Zero‐field single molecule magnet (SMM) behaviour has been observed for 2, where Raman relaxation and quantum tunneling of magnetization (QTM) played a role in magnetization relaxation. The Cu−O−Ln angle well explains the magnetic exchange coupling occurring in the complexes. BS‐DFT calculation for the complexes provides an estimate of the exchange interactions between the paramagnetic centres. Ab initio calculations performed for complex 2 established a good correlation to the experimental relaxation dynamics. [ABSTRACT FROM AUTHOR]

Chalcogenide phase‐change materials (PCMs) are a promising candidate for advanced memory and computing technologies. PCM‐based random access memories have entered the global memory market as storage‐class memory. In these products, the element arsenic plays an essential role in the selector layers, but how arsenic stabilizes the thermal stability of the chalcogenide glass remains elusive. Herein, thorough ab initio simulations are carried out to understand the chemical bonding, electronic structure, and optical properties of an important arsenic alloy As2Te3 in both crystalline and amorphous forms. In comparison with the homologue alloy Sb2Te3, the importance of homopolar bonds in stabilizing the amorphous phase of As2Te3 is revealed. Also, a strategy for the design of AsxSb2−xTe3 alloys with optimal material properties for nonvolatile photonic phase‐change applications is proposed. [ABSTRACT FROM AUTHOR]

Ab initio methods were used to determine the influence of tetrel bond formation on the acidity. The systems composed of inorganic acids and tetrafluorides of 14 group elements have been tested ‐ HA/EF4, where HA = H2O, NH3, HF, HCN, HNC, HCNO, HOCN and E = C, Si, Ge, Sn or Pb. It turns out that the electron density flow involved with formation of tetrel bond to carbon‐based systems leads to negligible increase in acidity. In the case of the acceptor compounds based on the remaining 14 group elements however, the effect is much more apparent, as most of those compounds may be considered a Brønsted superacids. The electronic stability of anions formed after the deprotonation of aforementioned complexes has been investigated. Vast majority of the anions were found to exhibit significant electron binding energies. [ABSTRACT FROM AUTHOR]

Theoretical kinetics and thermochemistry investigations on the H‐atom abstraction reactions by H and O atoms and OH and HO2 radicals from Si−C−O‐containing species such as Si(CH3)4, Si(CH3)3(OH), Si(CH3)2(OH)2, and Si(CH3)(OH)3 have been carried out in this work. The geometry, vibrational frequencies, and hindrance potential for each species are calculated at the B3LYP/6‐31G(2df,p) level of theory with the single‐point energies calculated at the G4 level of theory. The composite methods G3 and G4 are utilized to derive enthalpies of formation at 0 K by the atomization reaction methodology. ΔHf(298 K), S(298 K), and Cp(T) are calculated by using the statistical thermodynamics method. Conventional transition state theory is used over a wide temperature range (298.15−2000 K) for H‐atom abstraction reactions by H, O, and HO2 radicals from the species mentioned above, and variational transition state theory is used for H‐atom abstraction reactions by the OH radical. The kinetic and thermodynamic parameters based on high‐level theoretical calculations are compared with the literature data. Reactivity comparison between the similar hydrocarbons and silicon‐organic compounds for H‐atom abstractions is explored. A large difference exists between these two different systems when H‐atom abstractions are on hydroxyl sites. [ABSTRACT FROM AUTHOR]

The thermochemical and dynamics of H‐abstraction reactions by H atoms have been investigated for large polycyclic aromatic hydrocarbons (PAHs) including triphenylene, benzo[e]pyrene, dibenzo[fg,op]naphtacene, and coronene using high‐level ab initio methods, UCCSD(T)‐F12. Highly accurate ground‐state potential energy surfaces were obtained and used to compute reliable kinetic data. The structures and vibrational frequencies of all species involved in these reactions have been calculated using the CAM‐B3LYP/6‐311++G(d,p) level of theory. The thermodynamic and kinetic properties have been computed at both used levels of theories. For each type of site, the rate constants were calculated in the 500–2500 K temperature range. The results demonstrate that the overall rate constants of H‐abstraction reactions from PAHs with H atoms are not sensitive to the PAHs and their structures. An overall rate constant expression for these processes regardless of the size and structure of the PAH considered is proposed: k(T) = 5.53 × 107 × T2.19exp(58.09(kJ mol−1)/RT). [ABSTRACT FROM AUTHOR]

With promising applications in cold storage and seawater desalination, various refrigerant gas hydrates are experimentally studied for their phase equilibrium behavior; however, the theoretical modeling to predict their formation conditions is under development. Although a high degree of lattice distortion is expected in these gas hydrates due to highly polar and nonspherical molecules of refrigerants, this issue is not addressed in the van der Waals–Platteeuw theory. With this research gap, we formulate a lattice distortion theory for both pure and mixed refrigerant hydrates. For the first time, ab initio methodology comprising the spin‐component scaled MP2 method with Dunning's basis set is implemented for estimating cavity potential of refrigerant hydrates. The extent of lattice distortion is documented in terms of reference chemical potential and enthalpy differences, which are obtained by regressing the Holder's equation with the experimental data of refrigerant hydrate formation. A critical observation is made that the reference properties linearly vary with the "Boltzmann weighted energy‐well depth" of the guest. Analyzing the accuracy of the model using average absolute relative deviation between experimental and predicted pressure of hydrate formation, the proposed lattice distortion model outperforms the existing thermodynamic models for variety of pure and mixed refrigerant hydrates. [ABSTRACT FROM AUTHOR]

We present the story of full three‐dimensional ab initio simulation techniques of dense plasmas based on the Kohn–Sham realization of the density functional theory, starting from early attempts using the Car–Parrinello method to the most recent approaches based on density matrix. We recall the decisive role played by two experiments, one on the Nova laser and the other at a much smaller scale, with pulsed electrical discharges. We emphasize that the essential roles of the Physics of Non‐Ideal Plasmas (PNP) and Strongly Coupled Coulomb Systems (SCCS) conference series were most results, and simulation tools were presented and discussed under the benevolent presence of Vladimir Fortov. [ABSTRACT FROM AUTHOR]

2‐Carbamido‐1,3‐indandione (CAID) is a new reliable fluorescent biomarker and it exists in two tautomeric forms: 2‐(hydroxyl‐aminomethylidene)‐indan‐1,3‐dione (A) and 2‐carboamide‐1‐hydroxy‐3‐oxo‐indan (B). The structures of the tautomers and the transition state for intramolecular proton transfer are located at MP2/6‐31+G(d) level for each magnitude and for opposite directions of the applied electric field. According to our SCS‐MP2/6‐31+G(d) field‐free calculations tautomer A prevails (59.3%) while variation of the electric field strength along the direction from the indandione moiety to the carbamido fragment (+x‐direction) leads to stabilization of tautomer B. The two tautomeric forms become isoenergetic at 2.571 V/Å when the applied electric field is parallel to the direction from amino to the hydroxyl group (−y‐direction) in CAID, and at 3.085 V/Å tautomer B (51.9%) is slightly favored. Apparently, an external electric field has a strong influence on the tautomeric equilibrium in the CAID molecule. [ABSTRACT FROM AUTHOR]

Recent studies of TiO2/TiS2 nanostructures with various morphologies have been reported, usually showing improved properties with applications from electronics and catalysis to solar cells and medicine. However, there is a limited number of studies on the crystal structures of TiO2/TiS2 compounds with corresponding properties. In this research, relevant crystal structures of TiO1–xSx (x = 0, 0.25, 0.5, 0.75 and 1) solid solutions were investigated using an ab initio method. For each composition, crystal structures adopting anatase, rutile and CdI2 structure type were calculated on LDA‐PZ and GGA‐PBE levels of theory. Novel phase transitions and predicted structures are presented, and apart from several interesting metastable structures, a very interesting pressure‐induced phase transition is found in the TiOS compound. Furthermore, electronic properties were studied through the dependence of semiconducting properties on dopant concentration. The first description of the electronic properties of the mixed TiO1–xSx compounds in crystal form has been presented, followed by a detailed study of the structure–property relationship, which will possibly have numerous industrial and technological applications. [ABSTRACT FROM AUTHOR]

Silicate liquids are important agents of thermal evolution, yet their thermal conductivity is largely unknown. Here, we determine the thermal conductivity of a silicate liquid by combining the Green‐Kubo method with a machine learning potential of ab initio quality over the entire pressure regime of the mantle. We find that the thermal conductivity of MgSiO3 liquid is 1.1 W m−1 K−1 at the 1 bar melting point, and 4.0 W m−1 K−1 at core‐mantle boundary conditions. The thermal conductivity increases with compression, while remaining nearly constant on isochoric heating. The pressure dependence arises from the increasing bulk modulus on compression, and the weak temperature dependence arises from the saturation of the phonon mean free path due to structural disorder. The thermal conductivity of silicate liquids is less than that of ambient mantle, a contrast that may be important for understanding melt generation, and heat flux from the core. Plain Language Summary: Silicate liquids, the major constituents of lavas and magmas, are present not only at Earth's surface, but also in the deep interior. If present at the core‐mantle boundary at a depth of 2,891 km, silicate liquids may affect the heat that flows from the core to the mantle. The material property that describes the ability to transport heat is the thermal conductivity. The thermal conductivity of silicate liquids, however, is largely unknown. In this study, we calculate the thermal conductivity of silicate liquids across Earth's mantle conditions, which is made possible by the potential developed based on machine learning methods. The results show that the thermal conductivity of silicate liquids at the core‐mantle boundary is around half of that of the ambient mantle. This thermally insulating silicate liquid would reduce the core‐mantle heat flux, and has fundamental impacts on many deep Earth processes. Key Points: A machine learning based potential with ab initio quality is developed for MgSiO3 liquid across Earth's mantle conditionsThermal conductivity of MgSiO3 melts increases with compression, while remaining nearly constant on isochoric heatingSilicate melt is thermally insulating at the core‐mantle boundary and may enhance the heterogeneity of core‐mantle heat flux [ABSTRACT FROM AUTHOR]

The majority of crystal structures are determined by the method of molecular replacement (MR). The range of application of MR is limited mainly by the need for an accurate search model. In most cases, pre‐existing experimentally determined structures are used as search models. In favorable cases, ab initio predicted structures have yielded search models adequate for MR. The ORF8 protein of SARS‐CoV‐2 represents a challenging case for MR using an ab initio prediction because ORF8 has an all β‐sheet fold and few orthologs. We previously determined experimentally the structure of ORF8 using the single anomalous dispersion (SAD) phasing method, having been unable to find an MR solution to the crystallographic phase problem. Following a report of an accurate prediction of the ORF8 structure, we assessed whether the predicted model would have succeeded as an MR search model. A phase problem solution was found, and the resulting structure was refined, yielding structural parameters equivalent to the original experimental solution. [ABSTRACT FROM AUTHOR]

A comprehensive study of the properties and reactivity of ethyl(S)‐lactate has been conducted. The conformational landscape, the enthalpy of formation of the ground state, ΔfH∘−(0K)=−600.2±2.2 kJ mol−1, the thermochemistry (entropy, specific heat, enthalpy function), adiabatic ionization energy, and the single bond dissociation energies are also mapped out. Unimolecular elimination reactions leading to water and ethyl acrylate or ethene and lactic acid proceed with barriers in excess of 250 kJ mol−1—with the latter always dominant. The chemical kinetics of the abstraction of H‐atoms from primary, secondary, tertiary, and alcoholic sites by the radicals H• and CH3• are calculated as well as the kinetics of addition reactions to the carbonyl bond. [ABSTRACT FROM AUTHOR]

The reaction of Br atoms with toluene was investigated by employing various quantum chemical methods and statistical rate theory calculations. Various composite methods such as CBS‐QB3, G3, and G4 were used to obtain the energy profiles of the Br + toluene reaction. Further single‐point calculations of the stationary points were performed at the CCSD(T)/cc‐pV(D,T)Z level of theory using B3LYP/cc‐pVTZ and MP2/aug‐cc‐pVDZ optimized geometries. Our calculations revealed several reaction pathways in the potential energy surface of the Br + toluene reaction. However, the reaction pathway that abstracts hydrogen atoms from the methyl site of toluene was found to be energetically the most favorable. This reaction pathway appears to proceed via a complex forming mechanism, similar to that seen in the reactions of cyclic ethers with Br atoms. Our calculations reveal that the reaction of a Br atom with toluene proceeds exclusively via intermediate complexes in an overall endothermic addition‐elimination mechanism. Based on the ab initio results, the standard enthalpies of formation of the product radicals and the rate coefficients for the relevant reaction pathways are computed. The calculated values of the enthalpy of formation are found to match excellently with the available literature data. Lowering the barrier height of hydrogen abstraction reaction at the methyl site by less than 4 kJ/mol, the calculated rate coefficients, kov(T) = 1.36 × 10–23T3.687 exp(−4.57 K/T) cm3 molecule–1 s–1, reproduced the experimental data excellently from 200 to 500 K. [ABSTRACT FROM AUTHOR]

New software, called Marbles, is introduced that employs SAXS intensities to predict the shape of membrane proteins embedded into membrane nanodiscs. To gain computational speed and efficient convergence, the strategy is based on a hybrid approach that allows one to account for the contribution of the nanodisc to the SAXS intensity through a semi‐analytical model, while the embedded membrane protein is treated as a set of beads, similarly to as in well known ab initio methods. The reliability and flexibility of this approach is proved by benchmarking the code, implemented in C++ with a Python interface, on a toy model and two proteins with very different geometry and size. [ABSTRACT FROM AUTHOR]

The half‐metallicity of Heusler alloys is quite sensitive to high pressure and disorder. To understand this phenomenon better, we systematically studied the half‐metallic nature, magnetism, phonon, and thermomechanical properties of FeCrTe and FeCrSe Heusler alloys under high pressure using ab initio calculations based on density functional theory. The ground‐state lattice constants for FeCrTe and FeCrSe alloys are 5.93 and 5.57 Å, respectively, consistent with available theoretical results. Formation energy, cohesive energy, elastic constants, and phonon dispersion confirmed that both compounds are thermodynamically and mechanically stable. The FeCrTe and FeCrSe alloys showed a half‐metallic character with a band gap of 0.68 and 0.58 eV at 0 GPa pressure, respectively, and magnetic moments of 2.01 μB for both alloys, using generalized gradient approximation (GGA) approximation. FeCrTe alloy changes from metallic to half‐metallic above 30 GPa pressure using GGA + U. The elastic properties were scrutinized, and it was found that, at 0 GPa pressure, FeCrTe is ductile, and FeCrSe is brittle. Under pressure, FeCrSe becomes brittle above 10 GPa pressure. Average sound velocity Vm, Debye temperature ƟD, and heat capacity CV were predicted under pressure. These outcomes will improve the integration of Fe‐based half‐Heusler alloys in spintronic devices. [ABSTRACT FROM AUTHOR]

The impact of solvent flexibility and electron correlation on the simulation results of Cu2+ in liquid ammonia has been investigated via an ab initio quantum mechanical charge field molecular dynamics (QMCF MD) simulation approach. To achieve this, three different simulation systems were considered in this study, namely Cu2+ in rigid and flexible ammonia at Hartree‐Fock (HF) level of theory, as well as resolution of identity second order Møller‐Plesset (MP2) perturbation theory in the rigid body case. In all cases, a stable octahedral [Cu(NH3)6]2+ complex subject to dynamic Jahn‐Teller distortions without the occurrence of ligand exchange was observed. The Cu2+ − NH3 distance in the first shell agrees well with the experimental and other theoretical data. In all three cases, the structural data shows that the rigid‐body ammonia model in conjunction with the HF level of theory provides accurate data for the first solvation shell, while at the same time, the computational demand and thus the achievable simulation time are much more beneficial. The vibrational analysis of the Cu2+ − NH3 interaction yields similar force constants in the three investigated systems indicating that there is no distinct difference on the dynamical properties of the first solvation shell. In addition to the QMCF MD simulations, a number of natural bond orbital (NBO) analyses were carried out, confirming the strong electrostatic character of the Cu2+ − NH3 interaction. [ABSTRACT FROM AUTHOR]

We report a comprehensive ab initio investigation of the conformers of dehydrogenated glycine radicals using the STO‐3G, 3‐21G, and aug‐cc‐pVDZ (aVDZ) basis sets and the UHF and UMP2 (H2N‐CH‐COOH and HN‐CH2‐COOH) as well as MCSCF and MRCI (H2N‐CH2‐COO) methods via two different conformational search strategies generating initial structures for optimizations by (a) removing H atoms from glycine conformers and (b) scanning torsional angles describing internal rotation along the CC, CN, and CO (except for H2N‐CH2‐COO) bonds of the radicals. We find four H2N‐CH‐COOH {InCH, IInCH, IIInCH, IVnCH} and seven HN‐CH2‐COOH {IpNH, IIpNH, IIInNH, IVpNH VnNH, VIpNH, VIIpNH} conformers with classical(adiabatic) relative energies of {0.00(0.00), 1.57(1.55), 5.25(5.03), 9.85(9.72)} and {0.00(0.00), 0.78(1.06), 1.93(2.08), 3.34(3.16), 3.39(3.29), 5.00(4.86), 9.27(8.87)} kcal/mol, respectively, obtained with UCCSD(T)‐F12b/aug‐cc‐pVTZ(+UCCSD(T)‐F12b/aVDZ ZPE correction) and four H2N‐CH2‐COO {IpCOO, IInCOO, IIIpCOO, IVnCOO} conformers with MRCI‐F12+Q/aVDZ(+MRCI/aVDZ ZPE correction) energies of {0.00(0.00), 1.65(1.64), 1.78(1.75), 2.21(2.21)} kcal/mol, where n and p denote C1 and Cs symmetry. The MRCI‐F12+Q[UCCSD(T)‐F12b] InCH → IpNH and InCH → IpCOO classical(adiabatic) isomerization energies are 18.51(17.32)[21.20(20.01)] and 31.88(31.66) kcal/mol, respectively. [ABSTRACT FROM AUTHOR]

To control steel quality during continuous casting and subsequent heat treatment, an understanding of the evolution laws of mechanical properties during the austenite transition and the underlying mechanisms is of importance. Herein, the peak separation method is used to investigate the expansion behaviors in low‐carbon steel. And the elastic properties of the matrix phase are calculated using the exact muffin‐tin orbitals (EMTO) method. A continuous evolution model of high‐temperature properties in the phase‐transition region is established for ab initio data and experimental results. The evolution laws of the tetragonal shear elastic constant C′ and Young's modulus E agree well with that of the high‐temperature strength. The critical temperature for ductility to brittleness is 850 °C. The matrix phase exhibits significantly brittleness character and increases slightly with decreasing temperature in single‐phase paramagnetic (PM) γ‐Fe region. The straightening zone temperature should be controlled above 950 °C to avoid cracks. In the austenite transition region, the drop rate of the magnetic moment reaches 18.90%. The findings suggest that the evolution law of mechanical properties of steels can be predicted from the elastic properties, especially during the austenite transition process, providing a basis for the prediction of material properties using ab initio methods. [ABSTRACT FROM AUTHOR]

Control of order–disorder phase transitions is a fundamental materials science challenge, underpinning the development of energy storage technologies such as solid oxide fuel cells and batteries, ultra‐high temperature ceramics, and durable nuclear waste forms. At present, the development of promising complex oxides for these applications is hindered by a poor understanding of how interfaces affect lattice disordering processes and defect transport. Here, the evolution of local disorder in ion‐irradiated La2Ti2O7/SrTiO3 thin film heterostructures is explored using a combination of high‐resolution scanning transmission electron microscopy, position‐averaged convergent beam electron diffraction, electron energy loss spectroscopy, and ab initio simulations. Highly non‐uniform lattice disordering driven by asymmetric oxygen vacancy formation across the interface is observed. Theory calculations indicate that this asymmetry results from differences in the polyhedral connectivity and vacancy formation energies of the two interface components, suggesting ways to manipulate lattice disorder in functional oxide heterostructures. [ABSTRACT FROM AUTHOR]

An ab initio study, using the coupled cluster calculations (CCSD) method was conducted to investigate the kinetics of the ozone degradation in gas and aqueous phases considering the reaction of ozone with the hydroperoxyl radical. Two potential transition state paths, oxygen and hydrogen transfer, are studied and compared. It was revealed by the ab initio quantum chemical calculations that the calculated overall rate constant in the gas phase differs by approximately an order of magnitude from measured values. However, the calculated selectivity (branching fraction), which was measured directly with isotope studies of hydrogen atom transfer, is almost exactly equal to the experimental value at 298.15 K. The sensitivity analysis showed that adding the reaction between ozone and hydroperoxyl radical to the kinetic model accelerates the decomposition process by more than four times in the aqueous phase (pH = 7–8.5), and for an order of magnitude change in the rate constant of this reaction, the decomposition half‐life changes by 20–45 %. This result might affect our understanding of atmospheric ozone chemistry. [ABSTRACT FROM AUTHOR]

Ceramic coatings often suffer from the formation and expansion of microcracks, which leads to a failure of the protective function. In this work, we observed self‐healing of the microcracks in the TiSiN/Ag multilayer coating upon heating. This behavior can be attributed to diffusion of the Ag atoms to the cracks in the multilayer coating, while similar cracks in the TiSiN monolayer coating remain unchanged after the same treatment. Furthermore, the TiSiN/Ag coating with healed cracks possesses similar electrochemical corrosion and biofouling properties to the as‐deposited one, suggesting that TiSiN/Ag is a promising system in marine engineering applications. The mechanism of self‐healing was explained by kinetic simulations based on ab initio molecular dynamics and the diffusion activation energies of Ag in irregular ceramic structures have been calculated. The here adopted theoretical method also provides a new pathway for exploring new coating systems with a potential self‐healing function. [ABSTRACT FROM AUTHOR]

Thermochemistry and kinetic pathways on the 2‐butanone‐4‐yl (CH3C(=O)CH2CH2•) + O2 reaction system are determined. Standard enthalpies, entropies, and heat capacities are evaluated using the G3MP2B3, G3, G3MP3, CBS‐QB3 ab initio methods, and the B3LYP/6‐311g(d,p) density functional calculation method. The CH3C(=O)CH2CH2• radical + O2 association reaction forms a chemically activated peroxy radical with 35 kcal mol−1 excess of energy. The chemically activated adduct can undergo RO−O bond dissociation, rearrangement via intramolecular hydrogen transfer reactions to form hydroperoxide‐alkyl radicals, or eliminate HO2 and OH. The hydroperoxide‐alkyl radical intermediates can undergo further reactions forming ketones, cyclic ethers, OH radicals, ketene, formaldehyde, or oxiranes. A relatively new path showing a low barrier and resulting in reactive product sets involves peroxy radical attack on a carbonyl carbon atom in a cyclic transition state structure. It is shown to be important in ketones when the cyclic transition state has five or more central atoms. [ABSTRACT FROM AUTHOR]

The dissociation constant (pKa) of a drug is a key parameter in drug discovery and pharmaceutical formulation. The hydroxy substituent has a significant effect on the acidity of hydroxycinnamic acid. In this work, the acidic constants of coumaric acids are obtained experimentally by spectrophotometry using the chemometric method and calculated theoretically using ab initio quantum mechanical method at the HF/6‐31G* level of theory in combination with the SMD continuum solvation method. Rank annihilation factor analysis (RAFA) is an efficient chemometric technique based on the elimination of the contribution of one of the chemical components from the data matrix. RAFA cannot be performed because the pure spectrum of HA− is not available. So, two‐rank annihilation factor analysis (TRAFA) is proposed for the determination of the pKa OF H2A. A comparison between the pKa values obtained previously by TRAFA for the molecules o‐coumaric acid (4.13, 9.58), m‐coumaric acid (4.48, 10.35), and p‐coumaric acid (4.65, 9.92) makes it clear that there is good agreement between the results obtained by TRAFA and ab initio quantum mechanical method. [ABSTRACT FROM AUTHOR]