Search

We performed systematic ab initio calculations for the pyrolysis of phenyl formate (PF), the simplest aromatic ester, to establish the potential energy surfaces (PESs), thermodynamics and reaction kinetics. Reaction pathways considered in this work include direct bond fission and intramolecular H-shift, as well as subsequent radical decomposition and ipso-addition by H, O and OH radicals. The energies of reactants, transition states and products were determined at the ROCBS-QB3//M062X/cc-pVTZ level of theory. The standard enthalpy of formation of each species was determined using the atomization method, showing a good agreement with the literature results. For the PF unimolecular decomposition, the intramolecular H-shift reactions to produce phenol + CO and 2,4-cyclohexadienone + CO are the dominant decomposition pathways. Among the decomposition reactions of PF radicals, the isomerization and β -scission channels to form phenoxy + CO and C 6 H 4 OH + CO are the dominant pathways. Additionally, for the ipso-addition reactions, PF + H/O → HCOO + C 6 H 6 /C 6 H 5 O and PF + OH → HCOOH + C 6 H 5 O are the major pathways. Multi-well and multi-channel phenomenological rate constants were determined using the Rice–Ramsperger–Kassel–Marcus/master equation (RRKM/ME) method at 500−2000 K and the pressure range of 0.01 atm to the high-pressure limit. It is of interest to observe that the corresponding intermediates for PF radical decompositions with lower energy barriers are merged at higher temperatures and lower pressures. The rate constants of ipso-addition reactions are almost pressure-independence especially at higher temperatures (> 1000 K). [ABSTRACT FROM AUTHOR]

The quantification of He and Ne diffusion behavior in crystals rich in U and Th such as zircon is key for the interpretation of (U-Th)/4He and (U-Th)/21Ne thermochronometric ages. Multiple parameters such as chemical substitution, channel obstruction and damage can modify the diffusivity compared to a pristine structure. To investigate the impact of these parameters, we have conducted a theoretical diffusion study combining a series of methods and approaches to address the problem across the necessary range of scales (atomic to crystal size). First, using quantum calculation, we determine the different He and Ne insertion sites, insertion energies and diffusion pathways at the atomic scale for an ideal pristine zircon structure (i.e. damage free). These results serve as input for a 3D random walk simulation of atomic trajectories that provides diffusion coefficients for damage-free zircon crystals. Second, as natural zircon crystals are not perfect, we model the impact of different types of damage and diffusion pathway obstruction at the atomic level on He and Ne diffusion in 3D. The calculated He and Ne diffusion coefficients for pure ZrSiO 4 exhibit strongly anisotropic behavior and very high diffusivity along the c -axis, and with 3D, closure temperatures of −197 °C and −202 °C respectively. The results for He are comparable to previous DFT studies but strongly different from experimental diffusion results; results for Ne are similar in this respect. Modelling the impact of different types of damage (vacancies, recoil, fission, voids or fluid inclusions) and obstruction on He and Ne diffusion reveals important implications for the (U-Th)/He and (U-Th)/Ne thermochronometers. First, obstruction alone does not significantly modify He and Ne diffusion except to reduce anisotropy. Second, trapping is the primary mechanism altering He and Ne diffusion even at low dose, and we predict the maximal trapping energies for He and Ne to be 164 and 320 kJ/mol, similar to values inferred from experimental data. We also propose that the closure temperature increases non-linearly with damage, with effective trapping energy increasing with dose until a threshold, possibly corresponding to a percolation transition, after which retentivity decreases. Based on field data sets we also anticipate a value for this threshold of around ∼2–5 × 1017 α/g, lower than previously proposed. We show Ne to be highly blocked by damage and predict similar diffusion behavior to He, but with higher retentivity. We demonstrate the importance of investigating rare gas diffusion at the atomic level for comparison with experimental data, in order to build a predictive diffusion law at different scales. [ABSTRACT FROM AUTHOR]

Thermal decomposition of 1-hexene at temperatures 295-1410 K was conducted using a flash pyrolysis micro-reactor coupled to laser-based vacuum ultraviolet photoionization time-of-flight mass spectrometer (VUV-PI-TOFMS). The decomposition mechanism of 1-hexene was developed with the help of theoretical calculation performed at the MRCI/cc-pvtz//CASSCF/6–31+ G (d,p) level. The γ -scission and diradical retro-ene reactions were determined as the main initial decomposition reactions in the temperature range 990-1240 K. Two diradical retro-ene reaction channels, 1,5-diradical and 1,6-diradical reactions, were proposed in order to interpret the appearance of the C 4 H 8 species. The 1,5-diradical retro-ene reaction involved a 1,5-diradical intermediate that subsequently decomposed via C C β -scissions to the C2, C3 and C4 products. The 1,6-diradical retro-ene reaction proceeded via a 1,6-diradical intermediate and C C β -scissions to produce the C2 and C4 species. The proposed diradical retro-ene mechanism was evidenced indirectly by the early product distribution of 1-hexene pyrolysis in a flow reactor at 1173 K determined by synchrotron radiation VUV-PI-TOFMS. It was verified in the flash pyrolysis of 1-heptene as well. [ABSTRACT FROM AUTHOR]

Theoretical investigations on the kinetics of pentan-2-ol radical decomposition and isomerization reactions have been carried out in this work, together with the thermochemistry data calculations for important species involved in the reaction process. The B2PLYPD3/6-311++G(d,p) level of theory was used to optimize the geometries of all of the reactants, transition states, products and also the hindered rotor treatment for lower frequency modes. Single-point energies of all species are determined at the ROCCSD(T) level using the cc-PVQZ and cc-pVTZ which were extrapolated to the complete basis set limit (CBS). RRKM/Master Equation has been solved to calculate the pressure- and temperature-dependent rate coefficients for all channels in the pressure range of 0.01–100 atm over 300–2000 K. Pressure and temperature dependent branching fractions of key species produced from different pentan-2-ol radicals shows that 1- and 2-pentene are important bimolecular products. The kinetics and thermochemistry data for the title reactions has been used in the part II of this work for model development for pentan-2-ol oxidation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Genetic algorithm optimizes interatomic potentials for cubic ZrO 2 and YSZ. • Developed potentials sufficiently reproduce energy, force, and stress from DFT. • The potentials enable fast and accurate evaluation of material properties of YSZ. Yttria stabilized zirconia (YSZ) is an important engineering ceramic oxide used for various applications, including solid electrolytes in solid oxide fuel cells due to its high ionic conductivity. Accurate and computationally inexpensive interatomic potentials for cubic ZrO 2 and YSZ are required to accommodate the large number of defect configurations originating from high concentrations of Y and oxygen vacancies and to statistically understand their properties in realistic time. In this study, a genetic algorithm has been used to optimize empirical interatomic potential parameters for cubic ZrO 2 and 10Y 2 O 3 mol% YSZ using energies, forces acting on atoms, and stresses generated by ab initio calculations as training data. The optimized potentials reproduce the structural, mechanical, and thermal properties as well as the ionic conduction properties more accurately than previously reported empirical interatomic potentials. The developed potentials will be useful for a statistical characterization of YSZ properties, combined with more accurate ab initio calculations. [ABSTRACT FROM AUTHOR]

[Display omitted] • The PECs of the four lowest Ω substates have been calculated using MRCI and DIRAC methods, respectively. • The transition dipole moment matrix elements in the A2Π 3/2,u - X2Π 3/2,g system have been calculated. • The line strengths and lifetimes of vibronic bands have been derived. • Enhancement factors for detecting the variation of α and μ have been calculated. The four lowest Ω substates (X 2Π 3/2,g , X 2Π 1/2,g , A 2Π 3/2,u and A 2Π 1/2,u) of the I 2 + cation have been studied by high-precision ab initio calculations in comparison with experimental high-resolution absorption spectra. The potential energy curves were calculated using the multi-reference configuration interaction (MRCI) method and Dirac method, respectively. Rovibrational levels of these electronic states were derived by solving the radial Schrödinger rovibrational equation. Molecular constants were obtained in fitting energy levels to a spectroscopic model. Using the fit spectroscopic constants and newly calculated transition dipole moment matrix elements, line strengths of vibronic bands in the A 2Π 3/2,u - X 2Π 3/2,g system, as well as Einstein A coefficients for 45 of these bands with ν′ = 11–19 and ν′′ = 1–5, have been derived. The Einstein A coefficients were used to compute radiative lifetimes of the ν′ = 11–19 vibrational levels of the A 2Π 3/2,u state. Enhancement factors for detecting the variation of the fine-structure constant (α) and the proton-to-electron mass ratio(µ) using transitions between nearly degenerate rovibronic levels of these low-lying states have been calculated. [ABSTRACT FROM AUTHOR]

New energy storage systems and recycling schemes are required to solve the increasing environmental and energy problems. Owing to the increasing cost of raw materials, scraps need to be recycled. Carbides can be used as hydrogen storage materials; however, their mechanical properties remain unclear. To fabricate high-quality carbides from scraps as potential candidates for hydrogen storage materials, it is necessary to understand the mechanical properties of the carbides when absorbing hydrogen atoms. In this study, we evaluated the thermodynamic stabilities, mechanical properties, and electronic structures of (Ti, M)C 1-x materials (M = W, Mg, Ni, and Al, x = 0 – 1. The effects of the carbon vacancies were examined using density functional theory calculations. Based on the results, the TiC 0.625 composition was stable at ambient temperature and pressure. Titanium carbides have shown potential for use in hydrogen storage applications at 0 ≤ x ≤ 0.375 , as the hardness decreases rapidly when x ≥ 0.375. In addition, the results indicate that (Ti, Al)C should mainly be used in the target hydrogen storage materials at a composition below x = 0.25. These findings support the design of hydrogen storage materials based on recycled carbides. [Display omitted] • One of the possible uses of primary recovered materials is as hydrogen storage materials (HSMs). • The thermodynamic stability, mechanical properties, and adsorption energy of the (Ti, M)C 1-x were predicted to guide HSMs. • The use of tungsten must be approached with caution, as an excessive hydrogen content can reduce the mechanical properties. • Our research explored the potentials of (Ti, Al)C as viable hydrogen storage materials. [ABSTRACT FROM AUTHOR]

We performed ab initio valence-space in-medium similarity renormalization group calculations based on chiral nucleon-nucleon and three-nucleon interactions to study the neutron-rich nuclei around N = 28 , where the experimental and theoretical evidence point to a rapid transition from spherical to rotational regimes. First, the rotational spectra of 40Mg, 42Si, and 44S are established theoretically, anchored by the calculated E 2 transition strength. The results suggest that 40Mg and 42Si exhibit large deformations. After that, the erosion of the N = 28 shell closure, especially the evolutions of shape deformation and the emergence of shape coexistence, are discussed in N = 28 even-even isotones ranging from 40Mg to 48Ca. Finally, the shell evolution of N = 28 in Mg and Si chains is discussed based on the experimental and predicted excitation energies of low-lying states. The results from our ab initio calculations align well with available experimental data, furnishing essential insights into the structure of neutron-rich nuclei, particularly deformations in the vicinity of 40Mg and 42Si. [ABSTRACT FROM AUTHOR]

MoAlB is considered the most promising material for oxidation resistance among the MAB phase family. However, the anisotropic oxidation mechanism at the atomic scale has not been fully investigated, which may limit its practical applications. In this work the anisotropic oxidation mechanism of MoAlB was first explored through systematic theoretical calculations, based on which an effective strategy to enhance its oxidation resistance was identified and successfully implemented in the experimental work. The theoretical calculation revealed that the anisotropic oxidation of MoAlB was primarily related to the difference in free energy of surface oxidation reactions due to the degrees of electron interaction localization of O-Al bonding. A series of candidates of various transition metal-doped MoAlB materials were then designed to improve the weaker surface of MoAlB for oxidation resistance enhancement. Among these candidates, Zr-doped MoAlB was selected to further evaluate the effects of doping on the anisotropic oxidation through the electronic structure and Ab initio molecular dynamics (AIMD). Finally, Zr-doped MoAlB was experimentally synthesized to validate the theoretical design. Non-isothermal oxidation kinetics analysis indicated that Zr doping can enhance the oxidation resistance of MoAlB by promoting the formation of a protective oxide scale and increasing the formation activation energy of volatile products, which finally reduced the thickness of the oxidation scale on the surface after isothermal oxidation of the bulk material. This work not only contributes to an in-depth understanding of the oxidation mechanisms in MoAlB but also presents a new approach to enhance its oxidation resistance and other Al containing ceramic materials beyond MAB phases. [Display omitted] [ABSTRACT FROM AUTHOR]

The long-acting parenteral formulation of the HIV integrase inhibitor cabotegravir (GSK744) is currently being developed to prevent HIV infections, benefiting from infrequent dosing and high efficacy. The crystal structure can affect the bioavailability and efficacy of cabotegravir. However, the stability determination of crystal structures of GSK744 have remained a challenge. Here, we introduced an ab initio protocol to determine the stability of the crystal structures of pharmaceutical molecules, which were obtained from crystal structure prediction process starting from the molecular diagram. Using GSK744 as a case study, the ab initio predicted that Gibbs free energy provides reliable further refinement of the predicted crystal structures and presents its capability for becoming a crystal stability determination approach in the future. The proposed work can assist in the comprehensive screening of pharmaceutical design and can provide structural predictions and stability evaluation for pharmaceutical crystals.

Comprehensive ab initio electronic structure calculations were performed for a newly developed deep-ultraviolet (DUV) non-linear optical (NLO) crystal Ca2B10O14F6 (CBOF) using the first principle method. Fifteen point defects including interstitial, vacancy, antisite, Frenkel, and Schottky of Ca, O, F, and B atoms in CBOF were thoroughly investigated as well as their effects on the optical absorption properties. Their formation energies and the equilibrium concentrations were also calculated by ab initio total energy calculations. The growth morphology was quantitatively analyzed using the Hartman–Perdok approach. The formation energy of interstitial F (Fi) and antisite defect OF were calculated to be approximately 0.33 eV and 0.83 eV, suggesting that they might be the dominant defects in the CBOF material. The absorption centers might be induced by the O and F vacancies (VF, VO), interstitial B and O (Oi, Bi), and the antisite defect O substitute of F (OF), which might be responsible for lowering the damage threshold of CBOF. The ionic conductivity might be increased by the Ca vacancy (Vca), and, therefore, the laser-induced damage threshold decreases.

A comprehensive analysis of optical and photoluminescence images obtained from practical multicrystalline silicon wafers is conducted, utilizing various machine learning models for dislocation cluster region extraction, grain segmentation, and crystal orientation prediction. As a result, a realistic 3D model that includes the generation point of dislocation clusters is built. Finite element stress analysis on the 3D model coupled with crystal growth simulation reveals inhomogeneous and complex stress distribution and that dislocation clusters are frequently formed along the slip plane with the highest shear stress among twelve equivalents, concentrated along bending grain boundaries (GBs). Multiscale analysis of the extracted GBs near the generation point of dislocation clusters combined with ab initio calculations has shown that the dislocation generation due to the concentration of shear stress is caused by the nanofacet formation associated with GB bending. This mechanism cannot be captured by the Haasen-Alexander-Sumino model. Thus, this research method reveals the existence of a dislocation generation mechanism unique to the multicrystalline structure. Multicrystalline informatics linking experimental, theoretical, computational, and data science on multicrystalline materials at multiple scales is expected to contribute to the advancement of materials science by unraveling complex phenomena in various multicrystalline materials., (© 2023 The Authors. Advanced Materials published by Wiley-VCH GmbH.)

The ability to accurately measure or predict several physicochemical properties of molecules which play a role as active substances in drugs can be of strategic importance for pharmacological applications, in addition to its possible interest in fundamental research. Chirality is a relevant feature in the characterization of drug molecules: enantiomers can show different pharmacological activity and adverse effects. The ability to separate stereoisomers and to assign their absolute configuration can thus be crucial. Circular dichroism (CD) spectra are a useful tool to distinguish between enantiomers. In this work we apply an in-house developed code, based on an efficient DFT approach for circular dichroism, to fully characterize the molecular optical properties in the case of few selected fundamental molecules for current medical and pharmaceutical research, namely avibactam, as representative of non β-lactam inhibitors, two cephems (cefepime and cefoxitin), as examples of β-lactam antibiotics, and idelalisib, as a recent relevant anticancer active substance to treat major leukemias. For the above molecules, in addition to their optical absorption spectra, we calculate their CD spectra within state-of-the-art computational techniques. We then investigate both the conformational and chemical sensitivity of absorption and CD spectra for the chosen molecules. The outcomes of the present research could be of fundamental importance to gain additional information on molecules involved in therapeutic protocols for severe diseases or in drug design.

The paper presents and discusses the results of performed calculations for YAlO3 (111) surfaces using a hybrid B3LYP description of exchange and correlation. Calculation results for SrTiO3, BaTiO3 and BaZrO3 (111) as well as YAlO3, SrTiO3, BaTiO3 and BaZrO3 (001) surfaces are listed for comparison purposes in order to point out systematic trends common for these four ABO3 perovskite (001) and (111) surfaces. According to performed ab initio calculations, the displacement of (001) and (111) surface metal atoms of YAlO3, SrTiO3, BaTiO3 and BaZrO3 perovskite, upper three surface layers for both AO and BO2 (001) as well as AO3 and B (111) surface terminations, in most cases, are considerably larger than that of oxygen atoms. The YAlO3, SrTiO3, BaTiO3 and BaZrO3 (001) surface energies for both calculated terminations, in most cases, are almost equal. In contrast, the (111) surface energies for both AO3 and B-terminations are quite different. Calculated (111) surface energies always are much larger than the (001) surface energies. As follows from performed ab initio calculations for YAlO3, SrTiO3, BaTiO3 and BaZrO3 perovskites, the AO- and BO2-terminated (001) as well as AO3- and B-terminated (111) surface bandgaps are almost always reduced with respect to their bulk bandgap values. [ABSTRACT FROM AUTHOR]

The lattice thermal conductivity (κlat) of MgSiO3 postperovskite (Mg‐PPv) under the lowermost mantle pressure (P) and temperature (T) conditions was calculated using density functional theory combining anharmonic lattice dynamics theory. The κlat of Mg‐PPv was found to be ~50% higher than that of MgSiO3 bridgmanite (Mg‐Brg) owing to the larger phonon group velocity and lifetime. The lateral variation in the core‐mantle boundary heat flux (qCMB) can be enhanced by the Brg‐PPv phase transition. We also found that the κlat along the c axis of Mg‐PPv is close to the conductivity of isotropic aggregate. This suggests that the effect of anisotropy in the κlat on qCMB would be minor if the transversely isotropic aggregate with the c axis vertical alignment, a potential source of seismic anisotropy in the D″ layer, is developed. Key Points: We perform ab initio anharmonic lattice dynamics simulations of MgSiO3 postperovskite under the lowermost mantle conditionsLattice thermal conductivity of postperovskite substantially increases associated with phase transition from bridgmaniteEffects of anisotropy in the lattice thermal conductivity of postperovskite on the core‐mantle boundary heat flux are minor [ABSTRACT FROM AUTHOR]

In this paper, an assessment of the quality of a solid solution of CdSe0.2Te0.8 is done by study of its transport properties. The description of the kinetic phenomena is carried on the base of the wave function and self-consistent potential for CdSexTe1 - x (x = 0.2) solid solution which were determined from the first principles using the projector augmented waves as implemented in the ABINIT code. The scattering processes were considered in the framework of short-range scattering models where the electron interaction with polar and nonpolar optical phonons, piezoelectric and acoustic phonons, static strain centers, neutral and ionized impurities was taken into account. The transition matrix elements were obtained by integration over the unit cell using three-dimensional B-spline interpolation. For crystals with impurity concentration of 5.6 × 1015 ÷ 5 × 1018 cm-3, the temperature dependences of electron mobility and Hall factor in the range 15 ÷ 1200 K are calculated. The theoretical curves obtained in the short-range approach differ qualitatively and quantitatively from those obtained within the long-range models in relaxation time approximation. [ABSTRACT FROM AUTHOR]

The magnetic structure of polymorphic Cr-Co-Ni medium entropy alloys is investigated as a function of temperature and chemical composition by ab initio calculations. Besides the thermal lattice expansion, the longitudinal spin fluctuations (LSFs) are accounted for in determining the magnetic state at finite temperature. We show that sizable local magnetic moments persist on all alloy components in the paramagnetic state for both face-centered cubic and hexagonal close-packed structures, and each alloy species exhibits particular temperature and concentration dependencies. The crucial role of LSFs for the finite temperature magnetic state and its impact on the temperature dependent elastic parameters are demonstrated. Unlabelled Image [ABSTRACT FROM AUTHOR]

• The carbon nanotubes enhanced conductive magnetic fluid was prepared. • The conductive magnetic fluid maintains the superparamagnetic properties. • The impact of functionalization was investigated by experiments and calculations. • The conductivity of the magnetic fluid shows anisotropy under magnetic field. In this research, conductive magnetic fluid is prepared using carbon nanotubes (CNTs) as enhancing phase. The fluid is a superparamagnetic material. Experimental results show that CNTs form conductive networks. Meanwhile, surface treatment of CNTs is not conducive to enhance the conductivity, which has been confirmed by our calculations. More interestingly, when we apply an external magnetic field, the conductivity of the magnetic fluid increases along the magnetic field direction, showing anisotropy. These unique properties of the conductive magnetic fluid make it very promising in microwave absorbers and electromagnetic shields. [ABSTRACT FROM AUTHOR]

To realize the efficient frequency conversion, the nonlinear ultraviolet crystal must exhibit strong second harmonic generation and possible phase-matching condition. The current first principles calculations predict that SrBi 2 B 2 O 7 represents potentially a new class of materials with such characteristics. For this aim, we present the first analysis of dynamical, bonding, linear and nonlinear optical properties of the SrBi 2 B 2 O 7 single crystal. To untangle such properties, both density functional theory calculation and topological analysis were used. It is found that the compound exhibits a wide indirect band gap and an interesting bonding motif. In particular, the distortion caused by the stereochemically active lone pair of the s -state in the Bi3+ unit favors the enhancement of local dipole moment. In addition, the refraction index, absorption spectrum, phase matching and second harmonic properties were calculated and analyzed. According to the results, SrBi 2 B 2 O 7 has a large d 33 s-order susceptibility component which makes it a very promising UV nonlinear optical material. • First ab intio calculations on the SrBi 2 B 2 O 7 crystal are presented. • Lattice parameters, band gap, phase matching and dipole moments are in agreement withexperimental data. • Electron localization function are used to analyze the bonding properties. • Second harmonic generation (SHG) properties are also calculated. • SHG are found very sensible to the combined effects of the SrO 6 /BiO 3 units. [ABSTRACT FROM AUTHOR]

We report a Na:−→B dative bond in the NaBH3− cluster, which was designed on the principle of minimum‐energy rupture, prepared by laser vaporization, and characterized by a synergy of anion photoelectron spectroscopy and electronic structure calculations. The global minimum of NaBH3− features a Na−B bond. Its preferred heterolytic dissociation conforms with the IUPAC definition of dative bond. The lone electron pair revealed on Na and the negative Laplacian of electron density at the bond critical point further confirm the dative nature of the Na−B bond. This study represents the first example of a Lewis adduct with an alkalide as the Lewis base. [ABSTRACT FROM AUTHOR]

For the development and optimization of classical effective force fields (FFs) commonly used in molecular dynamics (MD) simulations, often experimental data are required. An alternative fully-predictive approach is the use of simplified pair-specific, ab initio -based FFs (AI-FFs) derived from quantum calculations in the limit of zero density. This approach, which could successfully be employed in our recent work for methane (CH 4) and carbon dioxide (CO 2), has not been investigated for relatively large systems including propane (C 3 H 8). In the present study, C 3 H 8 was selected as model system to evaluate the predictive power of MD simulations with respect to the determination of the self-diffusion coefficient and viscosity. For this aim, a semi-rigid version of our new simplified all-atom AI-FF was applied over a broad density range from the superheated vapor to the gas state and supercritical region up to the compressed liquid state. To elucidate the effects of the AI-FF on the calculated dynamical properties of C 3 H 8 , corresponding MD simulations representing the first investigations for the studied thermodynamic states were also performed using commonly employed, effective literature FFs in the form of TraPPE and OPLS. With the exception of the compressed liquid state, it was found that our ab initio -based approach improves the prediction results for the self-diffusion coefficient and viscosity at the studied thermodynamic states corresponding to pressures between (0.1 and 5) MPa and temperatures between (293.15 and 403.15) K compared to the use of effective FFs. This could be demonstrated by comparison with the ab initio -based calculations at the limit of zero density and the scarce experimental data. It could be figured out that the combination of an all-atom and a rigid or semi-rigid representation in our ab initio -based FFs for C 3 H 8 as well as CH 4 and CO 2 suits well for a reliable simulation of dynamical properties over a broad density range. • MD simulation study of self-diffusion coefficient and viscosity of propane •All-atom force field based on ab initio -derived potential energy surface developed •Influence of degrees of freedom on simulated dynamical properties analyzed •Predictions in superheated vapor, gas, and supercritical state improved by new model •Transferability of force field to compressed liquid state with reasonable results [ABSTRACT FROM AUTHOR]

• The work provides an ab initio adiabatic potential, permanent dipole moment and static dipole polarizability for the ground state of argonium (ArH +) over a wide range of interatomic distances. • The present results could be useful to estimate the downward cascade radiative transitions as well as the radiative association and dissociative recombination rates for the astronomically important ArH + isotopologues. A high level electronic structure calculation of the Born–Oppenheimer (BO) potential, scalar-relativistic effect and adiabatic correction is performed for the X 1 Σ + ground state of astronomically important isotopologues of the ArH + cation. Particular attention is paid to both short and long distances, where experimental spectroscopic data is not yet available. The BO energy is obtained over a wide range of interatomic distances (R ∈ [0.5, 20] Å) in the framework of multi-reference coupled pair functional (MR-ACPF) and single-reference coupled-cluster (CCSD(T)) methods. The all-electrons basis sets of the def2- n ZVPP (n = 3 , 4) and n ZaPa-NR, aug-cc-pCV n Z (n = 3 − 6) quality are used to monitor energy convergence. The BO energies are corrected for the basis set superposition error (BSSE) via the counterpoise method and are reduced to the complete basis set (CBS) limit using alternative extrapolating schemes. The permanent dipole moment d (R) and static dipole polarizability α (R) are calculated using a finite-field method. The molecular structure parameters coincide with their empirical counterparts for low vibrational levels to within 0.1%. Implementation of the ab initio results to circumscribe our understanding of the chemical networks in interstellar space is discussed. [ABSTRACT FROM AUTHOR]

This article discusses the attempt to create the built-in lateral p-n junctions in a sheet of black phosphorene using the adsorbed organic molecules as dopants. Within the framework of the methods of the electron density functional and the ab initio pseudopotential, the valence electron density spatial distributions, the densities of electronic states, the band gaps and the core charges of a sheet of black phosphorene were obtained. On the sheet of black phosphorene, there was a homogeneous distribution of the valence electron density. The adsorption of carbamide molecules for diverse types of localization on the surface of a black phosphorene sheet led to the redistribution of electron density in it. It was evident that the charge regions of greater density in a black phosphorene sheet with adsorbed carbamide molecules were localized under the atoms of carbamide molecules, forming a common region of the electronic density elevated concentration. The removal of the molecules led to a decrease in their effect on the redistribution of the valence electron density in a black phosphorene sheet. The accumulation of the electric charge of a black phosphorene sheet in the region under the carbamide molecules in turn led to the emergence of regions on the black phosphorene sheet, in which the core charges changed the sign to the opposite. The homogeneity of the distribution of electron density in the black phosphorene sheet disappeared and areas of a spatial charge of different signs were formed. Such areas with charges of different sings create conditions, which are the main characteristic of p-n junctions. Also it was established that the adsorption of the black phosphorene sheet with carbamide molecules led to a change in conductivity of a black phosphorene sheet. [ABSTRACT FROM AUTHOR]

In this paper, we studied the effect of single- and co-substitution of Ti and Fe on vacancy formation and hydrogen desorption on MgH 2 (110) surface through first principles calculations. In the surface, we calculated and compared total electronic energies for all possible co-substitution systems in order to determine the preferential Ti and Fe co-substitution site. Substitution energy showed that Ti and Fe co-substitution is more energetically favourable than single-substitution of Ti or Fe in the surface. The bond length, DOS and Bader atomic charge were estimated in order to understand bonding mechanism between atoms. We also calculated formation energy for H, Mg and complex Mg-H vacancies and hydrogen desorption energies. More importantly, it was found that improvement in vacancy formation and hydrogen desorption becomes more obvious in Ti and Fe co-substitution system than single-substitution system. Our results indicated that Ti and Fe co-substitution in MgH 2 (110) surface could be more effective method to improve poor hydrogen desorption properties of MgH 2 than Ti or Fe single-substitution. • Ti and Fe co-substituted in MgH 2 (110) surface combine firmly each other. • Co-substitution is more favorable energetically than single-substitution. • Single or co-substitution of Ti and Fe brings a change in the band gap. • Dopants attract Mg and H atoms and make low ionicity of them. • Co-substitution brings further reform of vacancy formation and hydrogen desorption. We investigated the effect of single- and co-substitution of Ti and Fe on vacancy formation and hydrogen desorption in MgH 2 (110) surface through first principles calculations based on density functional theory. Image 1 [ABSTRACT FROM AUTHOR]

The Li 4 Ti 5 O 12 (LTO) defect spinel is known for its excellent durability of "10,000" cycle counts and high level of safety as an anode material in lithium-ion batteries, but it shows an intrinsic insulating property and poor electrochemical kinetics. Doping is a direct approach to manipulate the electronic conductivity of LTO. However, doping may induce multiple effects influencing the overall electrochemical kinetics, e.g. , changing the size of particles and the ionic and electronic conductivities. Here we systematically investigated the phase stability, electronic conductivity, and electrochemical kinetics of M-doped LTO (M = Na, K, Mg, Ca, Sr, Al, and Ga). With both ab initio calculations and experiments, the mechanism of electron transport within LTO is elucidated, the desired type of dopants for improving electronic conductivity of LTO is clarified, and the role of electronic conductivity in the electrochemical kinetics of LTO is revealed. These results provide an in-depth understanding of metal-doped LTO and would help the development of a variety of electrode materials. Image 1 [ABSTRACT FROM AUTHOR]

Reversible hydrogen storage in MgH 2 under mild conditions is a promising way for the realization of "Hydrogen Economy", in which the development of cheap and highly efficient catalysts is the major challenge. Herein, A two-dimensional layered Fe is prepared via a facile wet-chemical ball milling method and has been confirmed to greatly enhance the hydrogen storage performance of MgH 2. Minor addition of 5 wt% Fe nanosheets to MgH 2 decreases the onset desorption temperature to 182.1 °C and enables a quick release of 5.44 wt% H 2 within 10 min at 300 °C. Besides, the dehydrogenated sample takes up 6 wt% H 2 in 10 min under a hydrogen pressure of 3.2 MPa at 200 °C. With the doping of Fe nanosheets, the apparent activation energy of the dehydrogenation reaction for MgH 2 is reduced to 40.7 ± 1.0 kJ mol−1. Further ab initio calculations reveal that the presence of Fe extends the Mg–H bond length and reduces its bond strength. We believe that this work would shed light on designing plain metal for catalysis in the area of hydrogen storage and other energy-related issues. The well distributed Fe nanoparticles broken down from nanosheets contributed to the remarkable enhancement in hydrogen storage properties of MgH 2. Image 1 • Fe nanosheets were successfully prepared by a facile wet-chemical method. • Hydrogen could be released at 182.1 °C and absorbed at 75 °C for the composite. • The de/hydrogenation activation energy of the composite were significantly reduced. • Ab initio calculations revealed that Fe facilitated the breaking of the Mg–H bond. [ABSTRACT FROM AUTHOR]

The xcalib toolkit has been developed to calibrate the beam profile of an X‐ray free‐electron laser (XFEL) at the focal spot based on the experimental charge state distributions (CSDs) of light atoms. Characterization of the fluence distribution at the focal spot is essential to perform the volume integrations of physical quantities for a quantitative comparison between theoretical and experimental results, especially for fluence‐dependent quantities. The use of the CSDs of light atoms is advantageous because CSDs directly reflect experimental conditions at the focal spot, and the properties of light atoms have been well established in both theory and experiment. Theoretical CSDs are obtained using xatom, a toolkit to calculate atomic electronic structure and to simulate ionization dynamics of atoms exposed to intense XFEL pulses, which involves highly excited multiple core‐hole states. Employing a simple function with a few parameters, the spatial profile of an XFEL beam is determined by minimizing the difference between theoretical and experimental results. The optimization procedure employing the reinforcement learning technique can automatize and organize calibration procedures which, before, had been performed manually. xcalib has high flexibility, simultaneously combining different optimization methods, sets of charge states, and a wide range of parameter space. Hence, in combination with xatom, xcalib serves as a comprehensive tool to calibrate the fluence profile of a tightly focused XFEL beam in the interaction region. [ABSTRACT FROM AUTHOR]

We report the magnetic behavior of isolated Fe impurity atoms in Pd 1− x U x (0 ≤ x ≤ 0.12) alloys studied through measurements of the local susceptibility (χ loc) and spin relaxation time for 54Fe nuclear probe using the time differential perturbed angular distribution (TDPAD) technique. With an increase of the U concentration in Pd-U alloys, the magnetic response of Fe, exhibiting Curie-Weiss type χ loc (T), reflects a steady decrease of the giant magnetic moment arising from ferromagnetic polarization of host Pd-4d band electrons. Concomitantly, we find an exponential rise in the spin fluctuation temperature T SF. The experimental observation of U induced suppression of giant magnetic moment of Fe in Pd is supported by ab intio electronic structure calculations based on density functional theory. The results presented here support the idea that sign and strength of spin polarization of host conduction band electrons play a crucial role on the spin fluctuation rate and hence moment stability. • Fe shows Curie-Weiss type local susceptibility in Pd-U binary alloys. • Exponential rise in Spin fluctuation temperature T SF with Uranium concentration. • The sign and strength of spin polarization of host conduction band electrons play a major role in the spin fluctuation rate. • Beyond x = 0.12 (Pd 1− x U x), the Fe atoms become nonmagnetic due to large spin fluctuation. [ABSTRACT FROM AUTHOR]

Within the framework of the methods of the electron density functional and the ab initio pseudopotential, we have obtained the valence electron density spatial distribution, the densities of electron states, the widths of band gaps, the charges on combined regions, and the Coulomb potentials for graphene-based flexible 2D layered junctions, using author program complex. It is determined that the bending of the 2D layered junctions on the angle α leads to changes in the electronic properties of these junctions. In the graphene/graphane junction, there is clear charge redistribution with different signs in the regions of junctions. The presence in the heterojunctions of charge regions with different signs leads to the formation of potential barriers. The greatest potential jump is in the graphene/fluorographene junction. The greatest value of the band gap width is in the graphene/graphane junction. [ABSTRACT FROM AUTHOR]

Mass spectrometric analysis of the anionic products of interaction between platinum atomic anions, Pt−, and methane, CH4 and CD4, in a collision cell shows the preferred generation of [PtCH4]− and [PtCD4]− complexes and a low tendency toward dehydrogenation. [PtCH4]− is shown to be H−Pt−CH3− by a synergy between anion photoelectron spectroscopy and quantum chemical calculations, implying the rupture of a single C−H bond. The calculated reaction pathway accounts for the observed selective activation of methane by Pt−. This study presents the first example of methane activation by a single atomic anion. [ABSTRACT FROM AUTHOR]

Investigations concerning the nature of interactions must be considered an issue of primary importance in the chemical sciences. The dynamic and static natures of interactions were recently proposed based on the quantum theory of atoms in molecules dual functional analysis (QTAIM‐DFA). The nature of interactions is widely investigated under various conditions, which often results in the predictions of (very) different natures. The predicted nature should be well correlated to the observed parameters, especially for experimental scientists. The effects from the basis sets and levels of calculations on the predicted parameters are carefully examined, exemplified by the interaction distances in question, the QTAIM functions for the interactions, and the QTAIM‐DFA parameters. The effects are discussed for the total (basis set + level) terms and each term. The mechanisms of the total terms are also clarified for the QTAIM‐DFA parameters. The results provide a good guideline for discussion of the nature of interactions based on the calculated parameters under various calculation conditions. The results help to establish a reliable method to elucidate the nature of interactions, such as QTAIM‐DFA. [ABSTRACT FROM AUTHOR]

Highlight • [HMIM][FEP] is selected as optimal extractant to separate 1-butanol from ABE solution. • Extractant screening is conducted from 1200 ionic liquids with COSMO-RS model. • Hybrid extraction-distillation process – with [HMIM][FEP] and mesitylene are simulated. • Mechanism of the extracting process is uncovered by quantum calculation. Abstract Separation of 1-butanol from the model fermentation broth (98 wt% water + 2 wt% ABE, acetone: 1-butanol: ethanol = 3: 6: 1) using liquid-liquid extraction (LLE) was investigated in this paper. This investigation involved multi-scale simulations from ab initio calculation to process simulation. Firstly, suitable extractant was screened from ionic liquids (ILs) combined of 30 anions and 40 cations using conductor-like screening model for real solvent (COSMO-RS) model. Meanwhile, the equilibrium experiment of the system ABE solution+selected IL was conducted to verify the screening result. From the screening, [HMIM][FEP] was found to be an optimal extractant and the experimental data confirmed this screening result with a deviation of 3.54%. The continuous hybrid process consisting of extraction and distillation section with the selected IL was also simulated and compared with a referenced process selecting mesitylene as extractant using Aspen Plus to investigate the performance of IL in real industry. The simulated results showed that a higher mass purities and yields of acetone (≥99.5 wt%), ethanol (≥99.5 wt%) and 1-butanol (≥99.9 wt%) could be obtained with much lower capital cost and energy consumption when the extractant was compared from [HMIM][FEP] to mesitylene. The extractant consumption and the energy consumption could lower 10% and 4.4% in total, respectively. The ab initio calculation enabled a deep insight on the mechanism of IL in extraction. Obviously, the results uncovered by the ab initio calculation showed that interaction between IL and 1-butanol was much stronger than mesitylene. [ABSTRACT FROM AUTHOR]

• The PECs of the 10 Λ-S states have been calculated. • The predissociation of the A2Π state have been analyzed. • The spin-orbit coupling of the Λ-S states have been discussed. • The PECs of the 17 Ω states arising from 10 Λ-S states have been calculated. • The Λ-S compositions for Ω state of the low lying electronic states have been studied. Ab initio calculations on the low-lying electronic states of mercury hydride (HgH) have been performed with the internally contracted multireference configuration interaction method. The potential energy curves (PECs) of the 10 Λ-S states as well as the 17 Ω states generated from the Λ-S states after considering the spin-orbit effect have been investigated. The spectroscopic constants of the bound states have been calculated. Based on the computed PECs, the Λ-S compositions of some low-lying states, as well as the transition dipole moments, the Franck–Condon factors and the radiative lifetimes for several vibronic transitions have been acquired. Our computed results should be valuable for further experimental research on the molecular electronic structure and properties of HgH molecules. [ABSTRACT FROM AUTHOR]

In this work, we use the full potential linearized augmented plane wave (FP-LAPW + lo) method under the framework of spin polarization density functional theory (SP-DFT) to study the structural properties of diluted magnetic semiconductors alloys, Mg1−xCrxSe (x = 0.25, 0.50 and 0.75), in the rock–salt ferromagnetic phase by using the WC-Cohen GGA approximation. To compute the electronic and magnetic properties of our compounds, we have used the Tran Blaha modified Becke–Johnson potential (TB-mBJ) combined with PBE approximation. The results of electronic properties show that our compounds have a half-metallic behavior with a spin polarization of 100% at the Fermi level. Moreover, at all concentrations, the magnetic moment has been estimated as equal to 4.0 (μB). Furthermore, to validate the effects resulting from the exchange splitting process, we calculate the values of the spin-exchange constants N0α and N0β, respectively. Finally, we present in detail the effects of the temperature and the pressure on some macroscopic thermodynamic parameters by using the quasi-harmonic Debye model. [ABSTRACT FROM AUTHOR]

Abstract We propose the development of Ni-stabilizing electrolyte additives to fundamentally prevent the degradation of Ni-rich layered cathode systems in lithium-ion batteries because unstable surface Ni and the dissolved Ni2+ are the major problems of those systems. The Ni2+-affinity is investigated as a key factor of the Ni-stabilizing additives. However, when providing a noble function to the electrolyte additive, the redox stability of the additives should be also understood. Thus, in addition to the intrinsic oxidation energy, the protonation and dehydrogenation energies of the additive molecules are calculated to determine the H-transfer-driven electrolyte oxidation. The Li+-complexation is considered to model the electrolyte reduction. We investigate the molecular-leveled computed factors of electrolyte materials using fully automated high-throughput ab initio calculations. Those computed factors for representative molecules based on CO 3 , SO 4 , SO 3 , SO 2 , PC 3 , PO 3 , and OPO 3 , which are of great interest as major parts of electrolyte materials, are discussed to guide the additive development. In particular, SO 2 and OPO 3 molecules, which can strongly stabilize Ni2+ in a structurally stable form, have great advantages as Ni-stabilizing electrolyte additives for completion of Ni-rich layered cathode systems. Graphical abstract Image 1 Highlights • Ni-stabilizing additive is proposed for Ni-rich layered cathode systems. • Ni2+-affinity is a key factor of Ni-stabilizing additives. • The redox stability of additives is modeled considering intermolecular reaction. • The molecular-leveled computed factors of various molecules are compared. • SO 2 and OPO 3 have great advantages as a major part of the Ni-stabilizing additive. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • UVPD spectrum of GMPH+ ion was measured by IR-laser ablation of droplet beam. • The three types of anti glycosyl-bond conformations with a keto form were observed. • A quadrupole ion trap with 70 ms trap time is essential for conformer separation. Abstract Photodissociation (PD) spectroscopy of protonated guanosine monophosphate (GMPH+) ions was performed using IR-laser ablation of droplet beam and quadruple ion trap techniques. Photofragmentation of GMPH+ gave a protonated guanine ion (GH+) as the main product. A wide-range PD spectrum (3.9–5.4 eV) monitored by the GH+ ion intensity showed four characteristic electronic transitions related to their three different anti glycosyl-bond conformers of GMPH+, which were identified by their π-π* transitions based on time dependent density functional theory calculation. Furthermore, the narrow-bandwidth PD spectrum (4.28–4.33 eV) shows the existence of syn glycosyl-bond conformation with keto form. [ABSTRACT FROM AUTHOR]

The anharmonic force fields and spectroscopic constants of the electronic ground state ( X ˜ 1 A ′ ) for H2AsO are calculated employing DFT (B3LYP, B3PW91, and B3P86) and MP2 methods with the aug-cc-pVQZ and aug-cc-pV5Z basis sets. The calculated equilibrium geometries, ground state rotational constants, harmonic frequencies, and anharmonic constants of H2AsO are in comparison with the experimental or previous theoretical data. The best agreement is found at the B3PW91/aug-cc-pV5Z theoretical level. The theoretically predicted fundamental vibrational frequencies, vibration–rotation interaction constants, equilibrium quartic and sextic centrifugal distortion constants, Coriolis coupling constants, cubic and quartic force constants of H2AsO are obtained at the B3PW91/aug-cc-pV5Z level and expected to provide help for the observation of the high-resolution rotational spectrum of H2AsO in the future. [ABSTRACT FROM AUTHOR]

NO2 fission is regarded to be the most important initial decomposition process of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20). In this study, four CL-20 conformers based on the ε-CL-20 were obtained after the optimization at m062x/cc-pvtz level, and the bond length, bond order and bond dissociation energy of the N-N bonds were examined to investigate the stability of these bonds. In addition, the rate constants and activation energy of the NO2 fission were evaluated using the microcanonical variational transition state theory (μVT). The calculation results have shown that N-N bonds in the case of pseudo-equatorial and axial of nitro groups are the most stable and the least stable, respectively, by evaluating the bond length, bond order and minimum energy path (MEP). The NO2 fission rate constants are affected by not only the stability of N-N bonds but also the repulsion forces from the other nitro groups, and the fission process for pseudo-equatorial positioning of nitro groups is easier to be accelerated due to the increase of the repulsion forces. The decomposition of CL-20 conformer may mainly originate from the fission of the pseudo-equatorial positioning of nitro groups, especially for CL-20 III conformer because of the significant low activation energy. [ABSTRACT FROM AUTHOR]