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The structural, mechanical, electronic, thermodynamic, and phonon characteristics of Sc 2 CdAl and Sc 2 ZnAl in L2 1 phase were the main focuses on this investigation. The density of states (DOS) and electronic band spectra signify the metallic behavior of the L2 1 phase of both materials. The impact of atomic arrangement with respect to the Wyckoff sites on the mechanical stability were additionally studied. The elastic constants of Sc 2 CdAl and Sc 2 ZnAl alloys indicated that these alloys convened Born mechanical stability criteria. Using the density functional perturbation theory's first-principle linear response method, complete phonon spectra have been acquired. Moreover, the quasi-harmonic approximation, specific heat capacity at constant volume, the internal free energy, entropy, and vibrational free energy variations of Sc 2 CdAl and Sc 2 ZnAl as full Heusler alloys have been utilized in examination the change over the temperature between 0 and 800 K. Both alloys might find application in real industrial applications. [ABSTRACT FROM AUTHOR]

The study of the mechanical properties of materials is of considerable fundamental and practical interest to most scientists. In this work the values of the equilibrium cell parameter, bulk modulus, its first derivative with respect to the pressure, and the speed of sound for diamond were calculated using the density functional theory (DFT) method and are 3.570 Å, 433.2 GPa, 3.71 and 17731.2 m/s. These parameters are found to be in good agreement with the experimental ones. The results of the study show that the mechanical properties of materials can be predicted with a high precision using the DFT method. [ABSTRACT FROM AUTHOR]

With the development of the chemical industry, benzene, toluene, ethylbenzene, and xylene (BTEX) have gradually become the major indoor air pollutants. Various gas treatment techniques are widely used to prevent the physical and mental health hazards of BTEX in semi-enclosed spaces. Chlorine dioxide (ClO2) is an alternative to chlorine as a secondary disinfectant with a strong oxidation ability, a wide range of action, and no carcinogenic effects. In addition, ClO2 has a unique permeability which allows it to eliminate volatile contaminants from the source. However, little attention has been paid to the removal of BTEX by ClO2, due to the difficulty of removing BTEX in semi-enclosed areas and the lack of testing methods for the reaction intermediates. Therefore, this study explored the performance of ClO2 advanced oxidation technology on both liquid and gaseous benzene, toluene, o-xylene, and m-xylene. The results showed that ClO2 was efficient in the removal of BTEX. The byproducts were detected by gas chromatography-mass spectrometry (GC-MS) and the reaction mechanism was speculated using the ab initio molecular orbital calculations method. The results demonstrated that ClO2 could remove the BTEX from the water and the air without causing secondary pollution.

Oxynitrides of cerium are expected to have many useful properties but have not been synthesized so far. We identified possible modifications of a not-yet-synthesized Ce3O3N compound, combining global search (GS) and data mining (DM) methods. Employing empirical potentials, structure candidates were obtained via global optimization on the energy landscape of Ce3O3N for different pressure values. Furthermore, additional feasible structure candidates were found using data mining of the ICSD database. The most promising structure candidates obtained were locally optimized at the ab initio level, and their E(V) curves were computed. The structure lowest in total energy, Ce3O3N-DM1, was found via local optimization starting from a data mining candidate and should be thermodynamically metastable up to high pressures.

Using density functional theory (DFT), we characterize the interaction of screw dislocations with interstitial impurities, in particular oxygen, nitrogen and carbon, in the HfNbTaTiZr alloy of body-centered cubic (BCC) structure. Considering different configurations representative of the disordered solid solution alloy, we evidence a noticeable core spreading of the screw dislocation whether with or without solute, associated with a wide range in dislocation-solute interaction energy, which is found to be mainly attractive for the three investigated impurities. This interaction energy is shown to be highly influenced by the type of the metal atoms in the neighbourhood of the solute. Notably the more BCC elements are present around the solute (either Nb or Ta), the more repulsive this interaction is. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • The supramolecular arrangement was studied using Hirshfeld surface analysis. • Physical chemistry properties were investigated using theoretical analysis. • The aqueous solvation effect was carried out using explicit and implicit approaches. Diclofenac diethylammonium belongs to the class of non-steroidal anti-inflammatory drugs, and it is widely used to relieve pain and reduce systemic inflammation. This drug exists in polymorphic forms, which can directly affect the ability to process the drug, as well as drug product dissolution, stability, and bioavailability. Considering the worldwide regulatory guidance for polymorphs in drug substances, a detailed structural analysis of two polymorphs exhibiting the anhydrous and monohydrated structures of diclofenac diethylammonium is presented here, using the supramolecular arrangement and its relationship with structural-physicochemical properties. The polymorph's structures show conformational differences in the carboxylic group caused by coordinated water molecules presented in the monohydrated polymorphic structure. Both polymorphs have the supramolecular arrangement stabilized by N H···O and C H···Cl intermolecular interactions, but the monohydrated molecule presents a strong O H···O intermolecular interaction due to the presence of a water molecule. Hirshfeld surface analysis showed C H···π and π···π contacts in the anhydrous and monohydrated polymorphs, respectively. Theoretical results, including solvent effect with explicit and implicit approaches for water, indicated the kinetic stability of the diclofenac diethylammonium drug and showed susceptible electrophilic attacks occurring in the region close to the carbonyl oxygen atom. [ABSTRACT FROM AUTHOR]

[Display omitted] • Yttria: metal oxide useful in technological applications. • 3-Aminopropyltriethoxy silane (APTES) is a suitable molecular system used as substrate for binding monoclonal antibodies to the surface of yttria nanoparticles. • Use of MD and DFT calculations to explain the interactions between yttria and APTES. • Chemisorption and physisorption of APTES on yttria surface. • Dative bond between nitrogen and yttrium atoms. In this paper, the development of Dreiding force field parameters to describe the structural features of yttria, has been done through a test and trial procedure. The parameters are used to study the interactions occurring between yttria's surface with 3-aminopropyltriethoxy silane (APTES) molecular system, which has been used as a substrate to bind a monoclonal antibody (anti-CYFRA-21-1) to an adequately prepared surface of yttria nanoparticles. The work reveals that, on an eventual hydroxyl free metal-oxide surfaces the APTES molecules would adsorb on it with two layers. The first is a chemisorbed layer that covers the entire surface (surface-density of 2.10 × 10−6 mol/m 2) with a direct partially covalent dative bond between the nitrogen of the amine group of APTES and the yttrium atoms on the surface. The second is a physisorbed layer over the first, with a half the surface-density (c.a. 1.05 × 10−6 mol/m 2), where the APTES molecules amine groups are pointing outwards with respect to the surface. This makes possible the direct covalent bonding between the amine groups, of the outer adsorbed layer of APTES molecules, with the carboxylic group of the monoclonal anti-CYFRA-21-1 antibody. Quantum mechanical calculations confirmed the outcome of the force field study. [ABSTRACT FROM AUTHOR]

As a rare earth element, yttrium has been widely concerned for improving the wear resistance, corrosion resistance, and especially oxidation resistance of TiAlN coatings. In this study, a novel theoretical and experimental strategy is designed to explore the influence of various Y contents on the structure, thermal stability and oxidation resistance of Ti 0.46 Al 0.54 N coatings. First-principle calculations show that Y-addition reduces the solubility of AlN in cubic TiAlN, coinciding with the additional wurtzite (w) phase as Y content increases above 0.05. Y-addition improves the thermal stability of TiAlN by retarding w-AlN formation along the most preferred decomposition sequence of TiAlYN → TiYN+AlN → TiN+AlN + YN. Alloying with moderate Y (z ≤ 0.04) into TiAlN leads to enhanced oxygen adsorption to form protective Al 2 O 3 layers, and thus optimizes the oxidation resistance. However, an excessive Y-addition (z ≥ 0.05) has the opposite effect due to the promoted transformation of TiO 2. • Incorporation of Y reduces the solubility of AlN in cubic TiAlYN. • Y-containing coatings exhibit superior thermal stability than TiAlN coating. • TiAlYN shows the decomposition sequence of TiAlYN → TiYN + AlN → TiN + AlN + YN. • Y-addition (≤4 at.%) is conducive to the oxidation resistance of TiAlN coatings. [ABSTRACT FROM AUTHOR]

• We provide a thermal equation of state for the magma ocean. • The compressibility of the silicate liquid is realized by the collapse of the second coordination sphere. • The viscosity of the magma ocean was extremely low. • The critical point of the bulk silicate Earth is close to 6000 K and 1.1–1.2 kbars, promoting mixing in the protolunar disk. As the protolunar disk formed by the giant impact with the incoming asteroid Theia started to cool, the Earth condensed in its center as a molten planet. The outer layer, rich in lithophile oxides, formed the magma ocean, whose dynamical behavior heavily influenced the entire evolution of the early Earth. Here, we employ first-principles molecular dynamics simulations to characterize the magma ocean in its initial stage. We compute the compressibility and the viscosity of the molten pyrolite, which best approximates the bulk silicate Earth composition. With an extensive set of calculations, we span the entire relevant pressure-temperature range. We provide a detailed analysis of the athermal and thermal equations of state in various formulations. We obtain a linear temperature dependence for the bulk modulus using the 4th order Birch-Murnaghan equation of state. We show that the liquid silicate accommodates compression by the collapse of the second Si-O coordination sphere, whose corresponding coordination number passes from about 24 at the surface of the magma ocean to about 40 at its deepest point. We found that pyrolite melts have a very low viscosity, about one order of magnitude lower than that of molten basalt. We also propose a revised position of the critical point of the bulk silicate Earth, which lies around 6000 K and 1.1–1.2 kbars. [ABSTRACT FROM AUTHOR]

Ethyl propionate shows great promise as a biodiesel molecule model. However, the current oxidation kinetic model falls short in accurately predicting its combustion behavior. Therefore, this study employed ab initio quantum chemistry methods to analyze the hydrogen abstraction reactions of ethyl propionate with various reactive radicals, including OH, O, H, CH 3 , C 2 H 3 , C 2 H 5 , HO 2 , CH 3 O and CH 3 O 2 , which play a critical role in refining the oxidation kinetics. Theoretical calculations were conducted to determine the rate constants and branching ratios for these reactions at temperatures ranging from 500 K to 2500 K using transition state theory, quasi-rigid rotor harmonic oscillator model, and tunneling correction. After updating the kinetics of hydrogen abstraction reactions in the oxidation mechanism proposed by Metcalfe et al., the modified model was validated by comparing the simulated mole fraction evolutions of ethyl propionate and major products in a jet-stirred reactor, ignition delay in a closed homogeneous batch reactor, and laminar flame speed with experimental data. The findings indicate that the modified model reliably reproduces the experimental data and significantly improves the prediction accuracy for low-temperature combustion of ethyl propionate when compared to the original model. [ABSTRACT FROM AUTHOR]

The excited state dipole moments of two positional isomers of dicyanobenzene have been determined from thermochromic shifts of the absorption and fluorescence emission spectra in ethyl acetate solution and compared to the results of ab initio calculations. We found that the dipole moments of excited states from thermochromic shifts closely resemble the ab initio values of the isolated molecule, while the results of conductor-like screening model (COSMO) using the same wave function model as for the isolated molecule, shows considerable deviations from the experimental values. It is shown that the dipole moments of the two cyano groups add up vectorially for both the ground and excited states. • Dipole moment of two isomeric dicyanobenzenes determined in ground and excited state from thermochromic shifts. • Comparison of the experimental results to SCS-CC2 calculations shows a very good agreement for excited state dipole moments of the isolated molecules. • Bad agreement with the results of COSMO calculations. • Additivity rule for dipole increments works in the ground state and the excited state. [Display omitted] [ABSTRACT FROM AUTHOR]

We have performed a quantum-mechanical study of off-stoichiometric Al 2 Ge 2 Mg τ -phase intermetallic compounds. Our calculations focused on evaluating the formation energy of static lattices, their elastic properties as well as free energy of formation including phonon contributions. While the stoichiometric Al 2 Ge 2 Mg τ phase was found thermodynamically, mechanically and dynamically stable, we have identified an off-stoichiometric composition Al 7 Ge 8 Mg 5 which exhibits the free energy of formation lower than the stoichiometric compound. The Al 7 Ge 8 Mg 5 was found both mechanically and dynamically stable as well. This off-stoichiometric compound has Mg atoms located also at the Al sublattice, i.e. these defects exhibit a stabilizing effect. Phonon contributions into the free energy of formation have turned out to be crucial for a proper description of the thermodynamic stability. In contrast, several other off-stoichiometric states are significantly thermodynamically destabilized by anti-site atoms at the Ge sublattice. The formation energy and the homogenized polycrystal Young's modulus are found anti-correlated indicating a connection between the thermodynamic and mechanical stability. Regarding the theoretical values of homogenized polycrystal Young's moduli, our measurements resulted in values quite close to the predicted ones. [Display omitted] • Experiments showed off-stoichiometric τ -phase Al 2 Ge 2 Mg thermodynamically more stable than the stoichiometric one. • Our quantum-mechanical calculations explain these findings and show the key stabilizing role of point defects and vibrational degrees of freedom. • Relations have been identified betwee the formation energy of and either the Ge concentration or the Young's modulus. [ABSTRACT FROM AUTHOR]

[Display omitted] Carbide nano-precipitates are commonly used to improve mechanical properties of steel. It has been experimentally observed that TiC, NbC, and VC carbide precipitates initially form as 'plate-like' particles oriented in the {1 0 0} planes of the ferrite lattice. These platelets share similarities with Guinier-Preston zones in Al-Cu alloys. The clustering of group IV and V transition metal atoms (M = Ti, Zr, Hf, V, Nb, Ta) in ferrite is studied using density functional theory. It is deduced that the transition metal carbides all form in a similar way. Furthermore, the transition from an initial M–C cluster to a NaCl-structured platelet to a NaCl-structured precipitate is examined through atomistic simulations using Modified Embedded Atom Method potentials. A route is established along which transition metal carbides form and transform into precipitates that possess the Baker-Nutting orientation relation with the ferrite matrix. [ABSTRACT FROM AUTHOR]

Electronically excited nitrogen atoms and N 2 molecules play a major role in nitrogen-rich atmospheres, specially under extreme conditions. Here we computationally explore several excited states of the N 2 O system and identify two new reactions involving the excited species N 2 (A) and N( 2 D) that can occur without electronic transitions. Their rate coefficients are estimated for the first time, and their implication to atmospheric models are discussed. We infer that the O( 3 P)+N 2 (A) → N( 2 D)+NO(X) channel should account for the total experimental NO production at room temperature. [Display omitted] • We survey many electronic states of NO 2 : 1 3 A", 2 3 A", 3 3 A", 4 3 A", 1 5 A' and 1 5 A". • Rate coefficients are calculated for the O( 3 P)+N 2 (X) → N( 2 D)+NO(X) reaction. • The O( 3 P)+N 2 (A) → N( 4 S)+NO(X) reaction is explored in the quintet states. • Within O( 3 P)+N 2 (A) → N( 4 S/ 2 D)+NO(X) we predict that only N(2D) is formed experimentally. [ABSTRACT FROM AUTHOR]

Cyclic ethers (CEs) can be promising future biofuel candidates. Most CEs possess physico-chemical and combustion indicators comparable to conventional fuels, making them suitable for internal combustion engines. This work computationally investigates the kinetic behaviors of hydrogen abstraction from 2-methyl tetrahydrofuran (2MTHF), one of the promising CEs, by hydroxyl radicals under combustion and atmospheric relevant conditions. The various reaction pathways were explored using the CCSD(T)/cc-pVTZ//M06-2X/aug-cc-pVTZ level of theory. The Rice–Ramsperger–Kassel–Marcus-based master equation (RRKM-ME) rate model, including treatments for hindered internal rotation and tunneling, was employed to describe time-dependent species profiles and pressure and temperature-dependent rate coefficients. Our kinetic model revealed that the H-abstraction proceeds via an addition-elimination mechanism forming reaction complexes at both the entrance and exit channels. Eight different reaction channels yielding five radical products were located. The reaction exhibited complex kinetics yielding a U-shaped Arrhenius behavior. An unusual occurrence of negative temperature dependence was observed at low temperatures, owing to the negative barrier height for the hydrogen abstraction reaction from the C-H bond at the vicinity of the O-atom. A shift in the reaction mechanism was observed with the dominance of the abstraction at Cα-H of 2MTHF ring (causing negative-T dependence) and at CH3 (positive-T dependence) at low and high temperatures, respectively. Interestingly, the pressure effect was observed at low temperatures, revealing the kinetic significance of the pre-reaction complex. Under atmospheric pressure, our theoretical rate coefficients showed excellent agreement with the available literature data. Our model nicely captured the negative temperature-dependent behaviors at low temperatures. Our predicted global rate coefficients can be expressed as k (T, 760 Torr) = 3.55 × 101 × T−4.72 × exp [−340.0 K/T] + 8.21 × 10−23 × T3.49 × exp [918.8 K/T] (cm3/molecule/s). Our work provides a detailed kinetic picture of the OH-initiated oxidation kinetics of 2MTHF. Hence, this information is useful for building a kinetic me chanism for methylated cyclic ethers.

The combination of spinel Li4Ti5O12 (LTO) with carbon nanostructures, such as graphene (G) and carbon nanotubes (CNTs), provides all of the required properties for modern chemical power sources such as Li-ion batteries (LIBs) and supercapacitors (SCs). G/LTO and CNT/LTO composites demonstrate a superior reversible capacity, cycling stability, and good rate performances. In this paper, an ab initio attempt to estimate the electronic and capacitive properties of such composites was made for the first time. It was found that the interaction between LTO particles and CNTs was higher than that with graphene due to the larger amount of transfer charge. Increasing the graphene concentration raised the Fermi level and enhanced the conductive properties of G/LTO composites. For CNT/LTO samples, the radius of CNT did not affect the Fermi level. For both G/LTO and CNT/LTO composites, an increase in the carbon ratio resulted in a similar reduction in quantum capacitance (QC). It was observed that during the charge cycle in the real experiment, the non-Faradaic process prevailed during the charge cycle, while the Faradaic process prevailed during the discharge cycle. The obtained results confirm and explain the experimental data and improve the understanding of the processes occurring in G/LTO and CNT/LTO composites for their usages in LIBs and SCs.

In this paper, DI defects are studied via experiments and calculations. The 2 MeV H+ is used to carry on an ion-beam-induced luminescence (IBIL) experiment to measure the in-situ luminescence of untreated and annealed 4H-SiC at 100 K. The results show that the luminescence intensity decreases rapidly with increasing H+ fluence, which means the losses of optical defect centers. In addition, the evident peak at 597 nm (2.07 eV) is the characteristic peak of 4H-SiC, and the weak peak between 400 nm and 450 nm is attributed to the DI optical center. Moreover, the first-principles calculation of 4H-SiC is adopted to discuss the origin of DI defects. The optical transition of the defect SiC(CSi)2 from q = 0 to q = 1 is considered the experimental value of the DI defect center.

The LiNa2 reactive system has recently received great attention in the experimental study of ultracold chemical reactions, but the corresponding theoretical calculations have not been carried out. Here, we report the first globally accurate ground-state LiNa2 potential energy surface (PES) using a Gaussian process model based on only 1776 actively selected high-level ab initio training points. The constructed PES had high precision and strong generalization capability. On the new PES, the quantum dynamics calculations on the Li(2S) + Na2(v = 0, j = 0) → LiNa + Na reaction were carried out in the 0.001–0.01 eV collision energy range using an improved time-dependent wave packet method. The calculated results indicate that this reaction is dominated by a complex-forming mechanism at low collision energies. The presented dynamics data provide guidance for experimental research, and the newly constructed PES could be further used for ultracold reaction dynamics calculations on this reactive system.

Polyethylene is one of the most used polymers in a variety of sectors. A typical technique used to assess aging is infrared spectroscopy. Under oxidation, the region of the spectrum that is most studied is the one containing the carbonyl signature. However, various carbonyl groups contribute to the carbonyl peak: ketones, aldehydes, esters, lactones, carboxylic acids, and more. A usual procedure to quantify each of them is the deconvolution of experimental peaks based on experimental assignments of infrared bands. In this paper, we complement this procedure, applied to two polyethylene types, with extended density functional theory (DFT) calculations of infrared spectra, using a polyethylene model mimicking the main features of a semicrystalline polymer. We compare theoretical frequencies and infrared intensities with parameters extracted from the literature that are used to, eventually, estimate concentrations. We provide an alternative estimation entirely based on theoretical data, showing that DFT can be a valuable tool to analyze, or at least complement, experimental data to assess polymer aging. The comparison of different deconvolution procedures raises the question of the contribution of conjugated ketones in the global carbonyl buildup, as well as that of ketones/alcohols pairs, or the relative concentration of esters and aldehydes.

Among all fluids, water has always been of special concern for scientists from a wide variety of research fields because of its rich behavior. In particular, some questions remain unanswered today regarding the temperature dependence of bulk and interfacial transport properties of supercooled and liquid water, for example, regarding the fundamentals of the violation of the Stokes-Einstein relation in the supercooled regime, or the subtle relation between structure and dynamical properties. We have studied the temperature dependence of the bulk transport properties from ab initio molecular dynamics based on density functional theory, down to the supercooled regime. We determined, from a selection of functionals, that the SCAN (strongly constrained and appropriately normed) functional best describes the experimental viscosity and selfdiffusion coefficient, although we found disagreements at lower temperatures. For a limited set of temperatures, we also explored the role of nuclear quantum effects on water dynamics using ab initio molecular dynamics that was accelerated by a recently introduced machine learning approach. We then investigated the molecularmechanisms underlying the different functionals' performance and assessed the validity of the Stokes-Einstein relation. We also explored the connection between structural properties and transport coefficients, verifying the validity of the excess entropy scaling relations for all functionals. These results pave the way for the prediction of the transport coefficients from the radial distribution function, thus helping to develop better functionals. In this respect, these results indicate the importance of describing the long-range features of the radial distribution function. [ABSTRACT FROM AUTHOR]

The understanding of self-heating effects and heat dissipation in semiconductor devices is a necessary element for the accurate modeling and prediction of reliability indicators. Unfortunately, the small dimensions, the complex device structures, and the presence of thin-oxidized interfacial layers make it impractical to determine these quantities experimentally. In this work, we calculate electrical conductances (${\sigma }$), electronic thermal conductances (${k}$), and their respective Lorenz numbers [ $\text {L}={k}/{(}\sigma {T}\,{)}$ ], for materials and relevant interfaces at the BEOL and MOL levels in advanced CMOS technologies. We progress from bulk to pure metal interfaces to realistically oxidized interfaces, and find the model works well, enabling a physical understanding of the impacts of oxidation, unavoidable in high-volume manufacturing. We find that Wiedemann–Franz (W–F) law applies very well for these metallic interfaces with Lorenz numbers being close to the bulk counterpart. We also find that interface oxidation exponentially increases the interface resistances. This can readily enable thermal characterization of these interfaces through electrical measurements, allowing accurate self-heating modeling for FinFET and beyond technologies. [ABSTRACT FROM AUTHOR]

Water adsorption in metal–organic frameworks has gained a lot of scientific attention recently due to the potential to be used in adsorption-based water capture. Functionalization of their organic linkers can tune water adsorption properties by increasing the hydrophilicity, thus altering the shape of the water adsorption isotherms and the overall water uptake. In this work, a large set of functional groups is screened for their interaction with water using ab initio calculations. The functional groups with the highest water affinities form two hydrogen bonds with the water molecule, acting as H-bond donor and H-bond acceptor simultaneously. Notably, the highest binding energy was calculated to be −12.7 Kcal/mol for the -OSO3H group at the RI-MP2/def2-TZVPP-level of theory, which is three times larger than the reference value. Subsequently, the effect of the functionalization strategy on the water uptake is examined on a selected set of functionalized MOF-74-III by performing Monte Carlo simulations. It was found that the specific groups can increase the hydrophilicity of the MOF and enhance the water uptake with respect to the parent MOF-74-III for relative humidity (RH) values up to 30%. The saturation water uptake exceeded 800 cm3/cm3 for all candidates, classifying them among the top performing materials for water harvesting. [ABSTRACT FROM AUTHOR]

We report on a new class of ZnO/ZnS nanomaterials based on the wurtzite/sphalerite architecture with improved electronic properties. Semiconducting properties of pristine ZnO and ZnS compounds and mixed ZnO1−xSx nanomaterials have been investigated using ab initio methods. In particular, we present the results of our theoretical investigation on the electronic structure of the ZnO1−xSx (x = 0.20, 0.25, 0.33, 0.50, 0.60, 0.66, and 0.75) nanocrystalline polytypes (2H, 3C, 4H, 5H, 6H, 8H, 9R, 12R, and 15R) calculated using hybrid PBE0 and HSE06 functionals. The main observations are the possibility of alternative polytypic nanomaterials, the effects of structural features of such polytypic nanostructures on semiconducting properties of ZnO/ZnS nanomaterials, the ability to tune the band gap as a function of sulfur content, as well as the influence of the location of sulfur layers in the structure that can dramatically affect electronic properties. Our study opens new fields of ZnO/ZnS band gap engineering on a multi-scale level with possible applications in photovoltaics, light-emitting diodes, laser diodes, heterojunction solar cells, infrared detectors, thermoelectrics, or/and nanostructured ceramics. [ABSTRACT FROM AUTHOR]

Using particle swarm optimization with density functional theory, we identify the positions of hydrogen in a hypothetical Mg-end-member of phase egg (MgSiO4H2) and predict the most stable crystal structures with MgSiO4H2 stoichiometry at pressures between 0 and 300 GPa. The particle swarm optimization method consistently and systematically identifies phase H as the energetically most stable structure in the pressure range 10–300 GPa at 0 K. Phase Mg-egg has a slightly higher energy compared to phase H at all relevant pressures, such that the energy difference nearly plateaus at high pressures; however, the combined efects of temperature and chemical substitutions may decrease or even reverse the energy difference between the two structures. We find a new MgSiO4H2 phase with the P43212 space group that has topological similarities to phase Mg-egg and is energetically preferred to phase H at 0–10 GPa and 0 K. We compute the free energies for phase Mg-egg, phase P43212, and phase H at 0–30 GPa within the quasi-harmonic approximation and find that the efect of temperature is relatively small. At 1800 K, the stability field of phase P43212 relative to the other polymorphs increases to 0–14 GPa, while pure phase Mg-egg remains energetically unfavorable at all pressures. Simulated X‑ray diffraction patterns and Raman spectra are provided for the three phases. Additionally, the crystallographic information for two metastable polymorphs with the P1 space group is provided. Our results have implications for the deep hydrogen cycle in that we identify two novel potential carrier phases for hydrogen in the mantles of terrestrial planets and assess their stability relative to phase H. We determine that further experimental and computational investigation of an extended compositional space remains necessary to establish the most stable dense hydrated silicate phases. [ABSTRACT FROM AUTHOR]

The vibrational entropy of a solid at finite temperature is investigated from the perspective of information theory. Ab initio molecular dynamics (AIMD) simulations generate ensembles of atomic configurations at finite temperature from which we obtain the N-body distribution of atomic displacements, ρ N . We calculate the information-theoretic entropy from the expectation value of ln ρ N . At a first level of approximation, treating individual atomic displacements independently, our method may be applied using Debye–Waller B-factors, allowing diffraction experiments to obtain an upper bound on the thermodynamic entropy. At the next level of approximation we correct the overestimation through inclusion of displacement covariances. We apply this approach to elemental body-centered cubic sodium and face-centered cubic aluminum, showing good agreement with experimental values above the Debye temperatures of the metals. Below the Debye temperatures, we extract an effective vibrational density of states from eigenvalues of the covariance matrix, and then evaluate the entropy quantum mechanically, again yielding good agreement with experiment down to low temperatures. Our method readily generalizes to complex solids, as we demonstrate for a high entropy alloy. Further, our method applies in cases where the quasiharmonic approximation fails, as we demonstrate by calculating the HCP/BCC transition in Ti. [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]

The term 'mathematical chemistry' is mostly associated with applications of graph theory in topological issues of 3D chemical structures, thought of as a collection of atoms as dots and bonds as lines. We propose here new directions in this field, coming from the side of theoretical chemistry approached with modern computational tools. Possible challenges are proposed in using ancillary tools of differential geometry for examining the potential energy surfaces of certain specific structural prototypes. Concretely, we describe here the geodesics on the surfaces related to the potential energy functions of the so-called E⊗e Jahn–Teller effect, a spontaneous symmetry-breaking phenomenon also known as a case of conical intersection. To illustrate the case, first-principles (ab initio) quantum chemical calculations are performed on the cyclo-propenyl molecular radical C3H3. [ABSTRACT FROM AUTHOR]

We report ab initio calculations of the S wave pairing gap in neutron matter calculated using realistic nuclear Hamiltonians that include two- and three-body interactions. We use a trial state, properly optimized to capture the essential pairing correlations, from which we extract ground state properties by means of auxiliary field diffusion Monte Carlo simulations. We extrapolate our results to the thermodynamic limit by studying the finite-size effects in the symmetry-restored projected Bardeen-Cooper-Schrieffer (PBCS) theory and compare our results to other ab initio studies done in the past. Our quantum Monte Carlo results for the pairing gap show a modest suppression with respect to the mean-field BCS values. These results can be connected to cold atom experiments, via the unitarity regime where fermionic superfluidity assumes a unified description, and they are important in the prediction of thermal properties and the cooling of neutron stars. [ABSTRACT FROM AUTHOR]

The structure of lead(II) is not well known in aqueous solution. The Hartree–Fock and second order Møller–Plesset levels of theory using the CEP, LANL2, and SDD effective core potentials in combination with their associated basis sets, or with the 6-31G* and 6-31+G* basis sets were used to calculate the energies, structures, and vibrational frequencies of Pb2+(H2O)n, n = 0–9, 18. The lead–oxygen distances and totally symmetric stretching frequency of the aqualead(II) ions from different levels of theory were compared with each other, and with solution measurements where available. The calculations support a hemidirected hexacoordinate structure. [ABSTRACT FROM AUTHOR]

Ternary compound YAlSi crystallizes with orthorhombic Cmcm symmetry. This structure contains Y–Si pairs of atoms, creating honeycomb-like sublattices. In this paper, we investigate the dynamical properties of the system, focusing on the chiral modes. These modes are associated with the circular motion of the atoms. We show that the chiral modes can be realized in the YAlSi compound, and it makes this compound suitable for further experimental study of the chiral phonons. [ABSTRACT FROM AUTHOR]

This study shows excellent NO2-sensing properties of tungsten oxide nanoparticles, prepared using a facile procedure which includes dissolution of metallic tungsten in hydrogen peroxide with subsequent low-temperature (400 °C) heating. We also conducted a thorough literature survey on sensor properties of tungsten oxide prepared by various means and found that the sensor response towards NO2 registered in this work achieved the highest level. The most intriguing feature of the material obtained was a highly reproducible sensor signal at room temperature which was more than 100 times higher than any reported previously for WO3. The probable reason for such high sensor response was the presence of two WO3 polymorphs (-WO3 and h-WO3) in the material synthesized using a peroxide-assisted route. In order to further investigate synthesizedWO3 materials, sophisticated experimental (XRD, SEM, TEM, BET) and theoretical (B3LYP, HSE) methods have been used, as well as resistance and sensor response measurements at various temperatures.

The discovery of superconductivity in hole-doped infinite-layer NdNiO2 — a transition metal (TM) oxide that is both isostructural and isoelectronic to cuprate superconductors—has lead to renewed enthusiasm in the hope of understanding the origin of unconventional superconductivity. Here, we investigate the electron-removal states in infinite-layered Ni1+ oxide, NdNiO2, which mimics hole doping, with the state-of-the-art many-body multireference quantum chemistry methods. From the analysis of the many-body wavefunction we find that the hole-doped d8 ground state of NdNiO2 is very different from the d8 ground state in isostructural cuprate analog CaCuO2, although the parent d9 ground states are for the most part identical. We show that the doped hole in NdNiO2 mainly localizes on the Ni 3dx2−y2 orbital to form a closed-shell singlet, and this singlet configuration contributes to ∼40% of the wavefunction. In contrast, in CaCuO2 the Zhang-Rice singlet configurations contribute to ∼65% of the wavefunction. With the help of the quantum information concept of entanglement entropy, we quantify the different types of electronic correlations in the nickelate and cuprate compounds, and find that the dynamic radial-type correlations within the Ni d manifold are persistent in hole-doped NdNiO2. As a result, the d8 multiplet effects are stronger and the additional hole foot-print is more three-dimensional in NdNiO2. Our analysis shows that the most commonly used three-band Hubbard model employed to express the doped scenario in cuprates represents ∼90% of the d8 wavefunction for CaCuO2, but such a model grossly approximates the d8 wavefunction for NdNiO2 as it only stands for ∼60% of the wavefunction.

We present an assessment of template-free modeling (FM) in CASP11and ROLL. Community-wide server performance suggested the use of automated scores similar to previous CASPs would provide a good system of evaluating performance, even in the absence of comprehensive manual assessment. The CASP11 FM category included several outstanding examples, including successful prediction by the Baker group of a 256-residue target (T0806-D1) that lacked sequence similarity to any existing template. The top server model prediction by Zhangs Quark, which was apparently selected and refined by several manual groups, encompassed the entire fold of target T0837-D1. Methods from the same two groups tended to dominate overall CASP11 FM and ROLL rankings. Comparison of top FM predictions with those from the previous CASP experiment revealed progress in the category, particularly reflected in high prediction accuracy for larger protein domains. FM prediction models for two cases were sufficient to provide functional insights that were otherwise not obtainable by traditional sequence analysis methods. Importantly, CASP11 abstracts revealed that alignment-based contact prediction methods brought about much of the CASP11 progress, producing both of the functionally relevant models as well as several of the other outstanding structure predictions. These methodological advances enabled de novo modeling of much larger domain structures than was previously possible and allowed prediction of functional sites. Proteins 2016; 84(Suppl 1):51-66. © 2015 Wiley Periodicals, Inc.

Gas-phase reactions are reliable strategies to explore the stability and activity of metal clusters, which can provide the information of products and the cluster activities by comparing the changes of the X, Y-axis of the mass spectrum before and after the reaction.Combined with ab initio calculation, we can deeply explore the structure of clusters, reaction intermediates and final products, explore the reaction thermodynamics and kinetic process,and reveal the essence and relationship between cluster structure,stability and reaction activity.In this paper,by investigating the gas-phase reaction mass spectra of Cun--clusters with NO and O2,,Agn- clusters with O2,and further combined with the ab initio calculation,novel open shell superatoms Cu18-,double closed shell superatoms Ag17- with unique stability are reported.Besides,we demonstrated the donation and back donation interactions between NO and Cun--.Chemisorption of O2 on Cu-2n+1,Cu-2n+1(or Ag-2n) clusters follows the double and single electron transfer mechanism, respectively.Among them, the behavior of O2 on Cu;;-is enabled by the spin conservation rule.By analogizing the cluster and O2 as base and acid respectively, we found a phenomenon that clusters with different alkalis pass through different degrees of spin excitation or dissociation barriers,and finally release almost the same heat for O2 dissociation. Based on this, a fully new mechanism of O2 on metal clusters was proposed: leveling effect of spin accommodation.Calculations of energy decomposition analysis-natural orbitals for chemical valence show that the activities of Cu; clusters towards NO and O2,Ag; clusters toward O2 are closely related to cluster geometry, electronic shell arrangement and energetics data. [ABSTRACT FROM AUTHOR]

This paper presents ab initio calculations within the Density Functional Theory (DFT) for the structural and optoelectronic properties of the alkali metal hydrides LiH and NaH in rocksalt structure (B1). This study used the Generalized Gradient Approximation (GGA) of Wu-Cohen to consider the electronic exchange and correlation interactions. In addition, the Tran-Blaha modified Becke-Johnson exchange potential was used with the GGA approach (GGA-TBmBJ) to calculate the band structure with high accuracy. The structural properties, namely the lattice parameter, the bulk modulus, and the pressure derivative of the bulk modulus were determined and found to be generally in good agreement with other research findings. Furthermore, the energy band gaps, the Density Of States (DOS), the static and high-frequency dielectric constant, along the refractive index were addressed and analyzed. These results could be useful for hydrogen storage purposes. [ABSTRACT FROM AUTHOR]

State-of-the-art acidic oxygen evolution reaction catalysts are mainly based on mixed oxides of titanium and iridium or ruthenium. Because of its high chemical corrosion resistance and stability in acid, TiO 2 is a promising support material, yet with poor electrical conductivity. We herein theoretically examined the stability and the electronic properties of substituted rutile-phase titania, in which Ti is partly replaced by elements of the fourth, fifth and sixth period. For negative values of the calculated segregation energy, we conclude that the heteroelement M forms a solid solution for 25% or 50% substitution. For these heteroelements, we calculate the electrical conductivity. Since it is known that the electronic structure of transition metal oxides strongly depends on the applied theoretical method, we performed self-consistent optimizations of the Hartree-Fock contribution to the exchange functional in a hybrid functional for every compound. Experimentally, two favorable and two unfavorable elements were synthesized with 25% foreign metal concentration. The most promising candidates to improve the electronic properties of titania are Ta and Nb. [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]

The emerging 2D g-C 2 N obtained increasingly more popularity in functional materials design, and its natural porosity can easily accommodate metal atoms, making itself more suitable for energy gases storage. In this study, we employed DFT computational studies to systematically solve the electronic structure of Li-doped g-C 2 N monolayer, and evaluate its performance in hydrogen storage. In our calculations, we found that each pore of g-C 2 N can adsorb at most three Li atoms that bind with pyridinic N atoms. We also noticed that considerable amount of charges were transferred from the adsorbed Li to the pristine materials, potentially enhancing its overall conductivity. The change of electronic structure also leads to its improved performance in H 2 adsorption, due to the fact that the electrostatic interactions between the adsorbed H 2 and Li can be largely enhanced. The optimised configurations of the Li-doped g-C 2 N with multiple adsorbed H 2 molecules were presented, and the fundamental mechanisms of adsorption were also investigated in details. The highest storage capacity of hydrogen by Li-doped g-C 2 N can reach to 7.8 wt%, much higher than the target value of 5.5 wt %, defined by the U.S department of energy (DOE). Moreover, except Li, we also found that the nitrogen atoms or the N-C bonds can also serve as active adsorption sites. The computational explorations conducted in this study actually indicates a promising prospect of alkali metals decorated 2D materials in the area of hydrogen storage; and we believe the performance of these kinds of novel materials can be further enhanced via more decent modifications. Computational Evaluation of Li-doped g-C 2 N Monolayer as Advanced Hydrogen Storage Media. [Display omitted] • Metal Li was applied to decorate g-C 2 N. • The Li-doped g-C 2 N shows high performance in hydrogen storage. • Electronic structure of this material was solved via DFT calculations. [ABSTRACT FROM AUTHOR]

Background: Macromolecule structure prediction remains a fundamental challenge of bioinformatics. Over the past several decades, the Rosetta framework has provided solutions to diverse challenges in computational biology. However, it is challenging to model RNA tertiary structures effectively when the de novo modeling of RNA involves solving a well-defined small puzzle. Methods: In this study, we introduce a stepwise Monte Carlo parallelization (SMCP) algorithm for RNA tertiary structure prediction. Millions of conformations were randomly searched using the Monte Carlo algorithm and stepwise ansatz hypothesis, and SMCP uses a parallel mechanism for efficient sampling. Moreover, to achieve better prediction accuracy and completeness, we judged and processed the modeling results. Results: A benchmark of nine single-stranded RNA loops drawn from riboswitches establishes the general ability of the algorithm to model RNA with high accuracy and integrity, including six motifs that cannot be solved by knowledge mining–based modeling algorithms. Experimental results show that the modeling accuracy of the SMCP algorithm is up to 0.14 Å, and the modeling integrity on this benchmark is extremely high. Conclusion: SMCP is an ab initio modeling algorithm that substantially outperforms previous algorithms in the Rosetta framework, especially in improving the accuracy and completeness of the model. It is expected that the work will provide new research ideas for macromolecular structure prediction in the future. In addition, this work will provide theoretical basis for the development of the biomedical field. [ABSTRACT FROM AUTHOR]