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Context: In this work, we investigate three elementary reactions involved in the production of glycine in the interstellar medium (ISM) employing trustworthy electronic structure and chemical kinetics methodologies. We considered three elementary reactions: HCOOH + NH 2 CH → NH 2 CH 2 COOH ( R 1 ), CH 3 COOH + NH → CH 2 COOH + NH 2 ( R 2 ) and CH 2 COOH + NH 2 → NH 2 CH 2 COOH ( R 3 ) under conditions consistent with hot molecular cores of massive star-forming regions. Our results indicate that the elementary reactions are feasible in these environments, with reaction barriers of 18.8 ( R 1 ) and 18.4 kcal · mol - 1 ( R 2 ). The rate coefficients for these reactions were calculated to be 1.4 × 10 - 17 and 9.3 × 10 - 16 cm 3 · molecule - 1 · s - 1 at 1000 K. Additionally, if the products of ( R 2 ) couple on a singlet surface, R 3 connects to the ground state of glycine via a barrierless path presenting a rate coefficient equal to 8.7 × 10 - 9 cm 3 · molecule - 1 · s - 1 at 298.15 K. Given that the molecules involved in these reactions have been detected in regions such as Sgr B2, our findings suggest that these elementary reactions should be included in mechanisms to study the production of glycine in such locations. Methods: The single-reference electronic structure calculations were carried out with the ORCA 4.1.2 package while the multi-reference calculations were performed with the Columbus 7.0 package. The DFT functionals employed were M06-2X, ω B97X, and ω B97X-D3, with the 6-31+G* and def2-TZVP, and for the wave function-based calculations, the CCSD(T), DLPNO-CCSD(T), MRCI, and CASSF methods were employed using the aug-cc-pVDZ, aug-cc-pVTZ, and aug-cc-pVQZ basis sets. The chemical kinetic calculations for the elementary reactions with well-defined saddle points were performed using the Pilgrim package employing the TST, CVT, and CVT/SCT approaches. [ABSTRACT FROM AUTHOR]

Nodal loop semimetals are topological materials with drumhead surface states characterized by reduced kinetic energy. If the Fermi energy of such a system is near these nondispersive states interaction among charge carriers substantially impacts their electronic structure. The emergence of magnetism in these surface states is one of the possible consequences. Ca P an already synthesized material possesses a remarkably large nodal loop which is situated exactly at the Fermi level of the bulk system. In the present work, we investigate how surface magnetism is impacted by surface reconstruction and lattice termination in finite slabs in this material. We show that a slight deviation from the stoichiometric occupation of Ca sites results in the stabilization of magnetic patterns. [ABSTRACT FROM AUTHOR]

Pilots are considered the final line of defense for aviation safety. Before becoming a pilot, an ab initio pilot must undergo systematic flight training. This study included 25 male flying cadets. Kendall’s coefficient of concordance was used to measure the regional homogeneity of the time series of a given voxel with its 26 nearest neighboring voxels. This operation was performed for all voxels to generate a regional homogeneity map for each participant based on Kendall’s coefficient of concordance. A partial correlation analysis was performed to examine the relationship between regional homogeneity maps and flight training hours. We found that the anterior cingulate cortex in the ab initio group was significantly positively correlated with flight hours. These results suggest a potential relationship between flight training experience and the functional properties of the anterior cingulate cortex. [ABSTRACT FROM AUTHOR]

We report on the temperature and field dependences of magnetization, magnetic specific heat, and magnetic entropy of the ferromagnetic SmFe 3 ( T C ≈ 655 K) and ferrimagnetic ErFe 3 ( T C ≈ 600 K, compensation temperature ≈ 230 K) compounds using the mean-field theory (MFT). The magnetocaloric effect (MCE), namely, the isothermal change in entropy (∆Sm) and the adiabatic change in temperature (∆Tad), is determined using the well-known Maxwell relation. Density Functional Theory (DFT), as implemented in the WIEN2k electronic code, is used to perform the ab-initio calculation of the elastic constants, bulk and shear moduli, and density-of-states. Using the electronic coefficient of specific heat ( γ e ) and the Debye temperature ( θ D ), the electronic and lattice contributions to the total specific heat and total entropy are computed, respectively. The ferrimagnetic ErFe 3 exhibits both direct and inverse MCE, while SmFe 3 exhibits only direct MCE effects. For SmFe 3 , the maximum Δ S m for a 7T field change is approximately 1.29 J/mol K. For the same field change, the maximum direct and inverse | Δ S m | for ErFe 3 are approximately 0.69 and 0.74 J/mol K, respectively. At their respective Curie temperatures, SmFe3 and ErFe3 exhibit adiabatic temperature changes of about 8 and 5 K, respectively, for a 7 T field change. The Arrott plots and universal curves, along with specific aspects of the thermomagnetic and magnetocaloric properties, are used to examine the order of the magnetic phase transition in these two systems. [ABSTRACT FROM AUTHOR]

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

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Context: In cellular environments, the reduction of disulfide bonds is pivotal for protein folding and synthesis. However, the intricate enzymatic mechanisms governing this process remain poorly understood. This study addresses this gap by investigating a disulfide bridge reduction reaction, serving as a model for comprehending electron and proton transfer in biological systems. Six potential mechanisms for reducing the dimethyl disulfide (DMDS) bridge through electron and proton capture were explored. Thermodynamic and kinetic analyses elucidated the sequence of proton and electron addition. MD-PMM, a method that combines molecular dynamics simulations and quantum-chemical calculations, was employed to compute the redox potential of the mechanism. This research provides valuable insights into the mechanisms and redox potentials involved in disulfide bridge reduction within proteins, offering an understanding of phenomena that are challenging to explore experimentally. Methods: All calculations used the Gaussian 09 software package at the MP2/6–311 + g(d,p) theory level. Visualization of the molecular orbitals and electron densities was conducted using Gaussview6. Molecular dynamics simulations were performed using GROMACS with the CHARMM36 force field. The PyMM program (Python Program for QM/MM Simulations Based on the Perturbed Matrix Method) is used to apply the Perturbed Matrix Method to MD simulations. [ABSTRACT FROM AUTHOR]

The geometries, energies, and vibrational frequencies of various isomers of HVO42−(H2O)n, n = 0–6 are calculated at various levels up to MP2/6−31 + G*. These properties are studied as a function of increasing cluster size. The calculations predict the vibrational frequencies, the full-widths at half-height, and a strong temperature and solvent dependence of the V–O(H) stretching and VOH bending vibration. [ABSTRACT FROM AUTHOR]

Excitation energies belonging to the (1s2)2s22p2, 2s22p3p, 2s2p3, 2s22p3s, and 2s22p3d configurations of carbon-like Na VI and Al VIII have been calculated with the multi-configuration Rayleigh–Ritz variation method and restricted variation method, as well as wavelengths, line strengths, oscillator strengths, transition rates for electric dipole transitions among these terms. High-accuracy calculations have been performed using a moderate scale of Slater basis function and accurate treatments of relativity, electron correlation, and quantum electrodynamic (QED) effects. The line strengths, transition oscillator strengths, and transition probabilities for the electric dipole transitions are determined. Deviations of line strengths between the length and velocity gauges are discussed, as well as with the experimentally compiled values from the National Institute for Standards and Technology (NIST) and other theoretical data wherever available. Furthermore, the accuracy of each electric dipole transition is assessed. The present results are accurate enough for identification of emission lines involving these terms and are also useful for precise spectral modeling and diagnosing in astrophysical and laboratory plasmas. [ABSTRACT FROM AUTHOR]

Using ab initio calculations, we studied the structural, mechanical, electronic and thermoelectric properties of the new double half-Heusler alloys, Ti2PdFeSb2 and Ti2PdRuSb2. Our calculations predict stable non-magnetic semiconducting phases with indirect bandgaps of 0.9 eV for Ti2PdFeSb2 and 0.7 eV for Ti2PdRuSb2. The calculated formation energies and elastic constants suggest that both alloys are thermodynamically as well as mechanically stable. A detailed thermoelectric response (S, κe, PF, ZT) of the alloys was investigated using semi-classical Boltzmann transport theory as implemented in BoltzTraP2 code. The lattice thermal conductivity κL was evaluated through the Slack model and shows a maximum value of 9.46Wm−1 K−1 for Ti2PdFeSb2 and 7.22Wm−1 K−1 for Ti2PdFeSb2, at 900 K. The collected results suggest that both compounds would be potential candidates for thermoelectric applications. [ABSTRACT FROM AUTHOR]

Context: This study rigorously investigates three 3d transition metal carbide (TMC) structures via LDA and GGA approximations. It examines cohesive energy (Ecoh), Vickers hardness (Hv), mechanical stability, and electronic properties. Notably, most 3d TMCs exhibit higher cohesive energy than nitrides, and rs-TiC demonstrates a Vickers hardness of 25.66 GPa, outperforming its nitride counterpart. The study employs theoretical calculations to expedite research, revealing mechanical stability in CrC and MnC (GGA) and CrC (LDA in cc structure), while all 3d TMCs in rs and seven in zb structures show stability. Charge transfer and bonding analysis reveal enhanced covalency along the series, influenced by the interplay between p orbitals of carbon and d orbitals of the metal. Most 3d TMCs exhibit metallic properties, excluding zb-TiC and zb-FeC in all phases. An inverse correlation between elastic constant C44 and electronic states near the Fermi level (EF) emerges, guiding applications and design. This study efficiently uncovers 3d TMC properties, offering insights for applications and design. Methods: We employed the Vienna ab initio Simulation software (VASP) to perform computations based on density functional theory (DFT). Our approach incorporated both the projector augmented wave (PAW) and PW91 general gradient approximation (GGA) methods within the local density approximation (LDA). [ABSTRACT FROM AUTHOR]

Three-dimensional ab initio potential energy surfaces of the interacting triple states 3A2 and 3B1 of the O3 molecule are constructed within the diabatization approach implemented in the MOLPRO package. These two states are responsible for the strongest singlet–triplet transitions in the Wulf band of O3. The molecular orbitals are optimized by the CASSCF method with the active space CAS(18, 12) involving three electronic states (X1A1, 3A2, and 3B1). The correlation energy is computed by icMRCI(Q). The influence of the basis set size on the accuracy of both the adiabatic excitation energy and origins of the vibronic transitions is analyzed. [ABSTRACT FROM AUTHOR]

Recently, photovoltaic solar cells have been revolutionized by adopting ABX3 halide perovskite materials as photoabsorbers. In the recent past, lead halide perovskites have attracted significant research interest. However, owing to its toxicity, alternative lead-free materials are currently being actively sought. In this work, we report the computational results of the structural, electronic, optical and elastic properties of the unexplored lead-free halide fluoroperovskite material ASiF3 (A = Li, Na, K and Rb) by means of first-principles calculations. The computed energetic and elastic properties assert that the formation of the ASiF3 cubic systems is energetically favourable and mechanically stable. According to the results, LiSiF3 and NaSiF3 are indirect bandgap semiconductors, which are not appropriate for solar cell applications. The calculated elastic, electronic and optical properties indicate that KSiF3 and RbSiF3 alloys are isotropic and exhibit high ductility. They have reasonable direct bandgaps, a small effective mass and good light absorption, making them suitable for single-junction photovoltaic cells and other optoelectronic applications in the visible and UV regions of the electromagnetic spectrum. [ABSTRACT FROM AUTHOR]

The electronic and thermoelectric properties of a CaSbK half-Heusler compound are investigated by combining ab initio calculations and Boltzmann transport theory. Taking into account the total energy as a function of the volume, the type I structure is found to be the most stable among the considered phases. The lattice stability of the compound is borne out by the results of mechanical, dynamical and thermodynamic properties. The electronic band structure calculations reveal an indirect bandgap (L–Γ) with high valence band degeneracy, leading to high DOS effective mass of holes. To assess the lattice thermal conductivity, both the Slack model and ShengBTE code are used. Electron and hole relaxation times are also computed using the deformation potential theory. The transport parameters are examined with respect to the carrier concentration at 300 K, 500 K and 700 K for n- and p-type doping. At 700 K, n-doped CaSbK exhibits a high figure of merit value of 1.54 with optimized carrier concentration of 2.8 × 1019 cm−3. Consequently, the CaSbK compound stands out as a promising candidate for thermoelectric applications. [ABSTRACT FROM AUTHOR]

Structural stability is a severe issue for the perovskite solar cells despite of their superior photovoltaic properties. Compositional engineering is an effective way to deal with the stability, so we have studied the structural, electronic, and optical properties of bromide mixed orthorhombic RbPb (I 1 - x Br x) 3 (where x = 0.25, 0.50, and 0.75) using density functional theory. The lowest energy band gaps of 2.288 eV and 2.986 eV for bromide mixing of x = 0.50 are obtained using PBE and TB-mBJ, respectively. In contrast, the mixed halide structures possess a smaller effective mass, facilitating a better carrier transport through it. PBE estimates excitons to be the Mott–Wannier type. However, the TB-mBJ predicts the exciton to be Frenkel type for bromide mixing of x = 0.75 and a Mott–Wannier type for all the other mixing under study. The spectroscopic limited maximum efficiency (SLME) was observed to be at the highest value of 14.0% for the equal admixture of I and Br using PBE. The calculated properties are consistent with the reported data of similar structures. [ABSTRACT FROM AUTHOR]

The effects of the stereoelectronic interaction on the structural and conformational properties of chloromethyl methyl ether (1), chloromethyl methyl sulfide (2), chloromethyl methyl selenide (3) were investigated by means of hybrid-density functional based method (B3LYP/Def2-TZVPP) and natural bond orbital (NBO) interpretation. According to the NBO analysis, the hyperconjugative generalized anomeric effect (HCGAE) decrease from compound 1 to 3, which explains the decrease of the energy discrepancy between their corresponding chiral gauche- and plane symmetrical anti-conformations. In contrast to the trend for the HCGAE, the determined dipole moment discrepancy between the chiral gauche- and plane symmetrical anti-conformations (µanti – µgauche) increase from compound 1 to 3. This fact reveals that there is no correlation between the variations of the conformational preferences in compounds 1–3 and the electrostatic effects associated with the dipole-dipole interactions. There is excellent agreement between the racemization energy barriers and the proportion between the GAE for compounds 2–3 and 1 (i.e., GAEx/GAE1) as well as the difference between the Wiberg bond indexes of C1–Y2 bonds (Δ[WBIanti-gauche(C1–Y2)]), (Y2 = O (1), S (2), Se (3)). The calculated differences the pairwise steric exchange energies (Δ(PSEEij)) can justify the decrease of the differences between the calculated total electronic energies of the gauche and anti conformations from compound 1 to 3. [ABSTRACT FROM AUTHOR]

Context: In guest–host interactions, guest molecules used for hydrogen bonding potential of clathrate hydrate cages are involved as "promoters" for hydrogen or methane storage. Among the promoter molecules, there are pinacolone and tert-butylmethyl ether containing oxygen atom, and tert-butyl amine among those containing nitrogen atom. The dimer and trimer interactions of these molecules with the water clusters were investigated. The cooperativity effect, which is a measure of the hydrogen bonding of these oxygen and nitrogen-containing complexes, was calculated and these complexes were analyzed. Moreover, molecular electrostatic potential (MEP) analysis was performed to determine intermolecular interactions. Clusters of several molecules may seem like a non-significant state of matter; however, in systematic studies with small clusters, important results can be obtained. Therefore, it is very useful to work with clusters to understand the properties of the dense phase, and this study aimed to examine the properties of structures, energies, infrared vibration frequencies, and topological parameters, which develop as a result of the interaction of structures in different clusters with water molecules. Methods: The MP2 level was performed using aug-cc-pVDZ basis set calculations for this study. Tight converting criteria were used in the optimization step. Harmonic vibrational modes were calculated at the MP2/aug-cc-pVDZ level. Each minima obtained from the MP2 level was subjected to single-point energy calculations using CCSD(T) levels with the aug-cc-pVDZ basis set by the Gaussian16 package program suite. The topological analyses were performed with non-covalent interaction (NCI). MEP surface of the complex was also composed by Gaussian program using the optimized geometry at a MP2/aug-cc-pvdz level. [ABSTRACT FROM AUTHOR]

Context: By means of ab initio molecular dynamics simulations, possible boron-rich amorphous silicon borides (BnSi1−n, 0.5 ≤ n ≤ 0.95) are generated and their microstructure, electrical properties and mechanical characters are scrutinized in details. As expected, the mean coordination number of each species increases progressively and more closed packed structures form with increasing B concentration. In all amorphous models, pentagonal pyramid-like configurations are observed and some of which lead to the development of B12 and B11Si icosahedrons. It should be noted that the B11Si icosahedron does not form in any crystalline silicon borides. Due to the affinity of B atoms to form cage-like clusters, phase separations (Si:B) are perceived in the most models. All simulated amorphous configurations are a semiconducting material on the basis of GGA+U calculations. The bulk modulus of the computer-generated amorphous compounds is in the range of 90 GPa to 182 GPa. As predictable, the Vickers hardness increases with increasing B content and reaches values of 25-33 GPa at 95% B concentration. Due to their electrical and mechanical properties, these materials might offer some practical applications in semiconductor technologies. Method: The density functional theory (DFT) based ab initio molecular dynamics (AIMD) simulations were used to generate B-rich amorphous configurations. [ABSTRACT FROM AUTHOR]

Mechanisms of structural stabilization of sI hydrates by CH4, H2S, H2, N2, Ar, Kr, Xe, CO2, C2H6, C3H6 gas molecules are studied by the density functional method. It is shown that the hydrate D- and T-cages are deformed and their radii are changed (up to –0.23%) upon the introduction of guest gas molecules. Binding energies of the gases in the D- and T-cages are calculated. It is established that molecules with diameters d < 5 Å and d > 5 Å stabilize better D- and T-cages, respectively. Two groups of gases can be distinguished, depending on the binding energy dependence on the molecule′s mass: molecular gases (dEb/dM ∈ (–0.008; –0.006) eV·mol/g) and atomic gases (dEb/dM ∈ (–0.002; –0.0015) eV·mol/g). It is shown that the orientation of extended CO2, C2H6, and C3H6 molecules along the long axis of the T-cage is most energetically favorable. Densities of electronic states N(E) are calculated for the unfilled sI hydrate and for sI hydrates containing CH4 and CO2. It is shown that the presence of a guest molecule decreases the energy of the electronic subsystem and increases the hydrate′s stability. [ABSTRACT FROM AUTHOR]

Using the density-functional theory (DFT) method, potential energy surfaces are calculated for M + C60 (M = He, Ne, Ar, HF) systems, where molecules M are encapsulated inside the fullerene C60 molecule. The frequencies of three-dimensional vibrations in these systems are calculated (259, 175, 340, and 109 cm–1, respectively). Vibrational rotation with moment increases these energies by value ( , 132, 170, and 96 cm–1, respectively). The Schrödinger equation is solved for the HF molecule motion inside the C60 cage. The Coriolis vibrational—rotational interaction is detected, where two types of rotational moments ( and l, where the former is the motion inside C60 and the latter is the HF rotation) are coupled and produce a total rotational moment, and these two motions are mixed. [ABSTRACT FROM AUTHOR]

Potentially superhard W 1 - x Z r x B 2 polymorphs, hP6-P6 3 /mmc-WB 2 and hP3-P6/mmm-WB 2 , were thoroughly analyzed with zirconium doping in the range of x=0-25%, within the framework of the first-principles density functional theory, from both a structural and a mechanical point of view. The obtained results were subsequently compared with the properties of material deposited by the magnetron sputtering method. All predicted structures are mechanically and thermodynamically stable. Theoretical calculations suggest a decrease in hardness H v and fracture toughness K IC of the hP6 phase with zirconium doping but no such effect on the hP3 phase. It was observed that an additional defect in the analyzed structure significantly weakens the hP6 phase but strengthens the hP3 phase. The deposited films are characterized by greater hardness but lower fracture toughness. The results of experiments show that not only is solid solution hardening responsible for strengthening the predicted new material but also the change in microstructure, the Hall–Petch effect and vacancies. [ABSTRACT FROM AUTHOR]

A search has been conducted, by means of ab initio molecular orbital theory, for potential tetrel-bonded complexes formed between the fluorinated methanes methyl fluoride, difluoromethane and fluoroform, and the related hydrides ammonia, water, hydrogen fluoride, phosphine, hydrogen sulphide and hydrogen chloride. Eleven such complexes have been identified, six containing CH3F and five CH2F2. The complexes are typically less strongly bound than their hydrogen-bonded counterparts, and the interaction energies vary in a consistent way with the periodic trend of the electron donors. The intermolecular separations and changes of the relevant intramolecular bond lengths, the wavenumber shifts of the critical vibrational modes and the extents of charge transfer correlate, by and large, with the strengths of interaction. [ABSTRACT FROM AUTHOR]

Crystal structure and phonon spectrum of rare-earth stannates R 2 Sn 2 O 7 and zirconates R 2 Zr 2 O 7 (R = La–Lu) with the pyrochlore structure were studied within the framework of DFT and MO LCAO approach. The calculations were performed by using hybrid functional PBE0 that take into account nonlocal exchange at the Hartree-Fock formalism. The calculation of the phonon spectrum at the Γ -point made it possible to supplement the available experimental data on the IR and Raman spectra of stannates and zirconates. In the framework of the ab initio approach, the change of the elastic properties of zirconium oxide t-ZrO 2 by doping the yttrium was studied. Calculations were performed in the CRYSTAL17 program designed to simulate periodic structures. [ABSTRACT FROM AUTHOR]

The article presents preliminary results of calculations of the potential energy of the interacting O3–O2 complex. The study of this complex is important for modeling the ozone formation reaction in the stratospheric layer of the Earth's atmosphere. Calculations were carried out from the first principles of the quantum theory (ab initio) using explicitly correlated spin-unrestricted coupled cluster method [UCCSD(T)–F12a] in combination with the correlation-consistent basis set [aug-cc-pVTZ] to describe molecular orbitals. The radial dependences obtained at selected angular orientations are discussed in comparison with the O3–N2 complex. [ABSTRACT FROM AUTHOR]

For the ultimate goal of adjusting the physical properties of the tin-carbide (SnC) semiconductor, a meticulous theoretical study based on density functional theory (DFT) and Korringa–Kohn–Rostoker (KKR) method combined with coherent potential approximation (CPA) on transition metals substitution is investigated. Iron (Fe) and chromium (Cr) ions have been chosen for their interesting magnetic properties (spin moment, Curie temperature). A value x corresponding to the substitution concentration is varied between 2% and 24% for both S n 1 - x C r x C and S n 1 - x F e x C compound types. All S n 1 - x F e x C compounds show a half-metallic ferromagnetic nature, while a similar behavior is also revealed for S n 1 - x C r x C compounds with x up to 12. Our self-consistent (SCF) spin-polarized calculations findings revealed that the main contributions to the net magnetization of our compound originate from Fe and Cr ions, with the partial spin moment of Fe is 3.68 μ B for 24 % and is around 2.4 μ B for Cr. The mean field approximation indicates that the Curie temperature reaches its highest value of 502.86K for Fe at the x-value of 12% , whereas with Cr substitution, the greatest value of 712K is found at x=24%. These findings show that S n 1 - x C r x C and S n 1 - x F e x C compounds are promising for spintronics applications. [ABSTRACT FROM AUTHOR]

The effect of pressure on band parameters and optical characteristics in the zinc-blende structure of InN has been investigated. An ab initio pseudopotential plane waves method has been used. At zero pressure, our results regarding the fundamental energy band gap, electron effective mass and many optical parameters concord well with recent experimental data. Monotonic and non-linear behavior of most quantities have been shown upon compression. The present study is useful for the use of zinc-blende InN in optoelectronics and microelectronics applications. [ABSTRACT FROM AUTHOR]

Dismutation reaction of superoxide radical catalyzed by EUK-134 has lower activation energy than non-catalytic reaction, and therefore, EUK-134 catalyzes dismutation reaction of superoxide radical. For non-catalytic dismutation reaction of hydrogen peroxide, there are three possible reaction paths, among which MEP3 has the lowest activation energy, and therefore, is thought to be the most probable reaction path. Dismutation reaction of hydrogen peroxide catalyzed by EUK-134 occurs in two successive steps and has lower energy barrier than non-catalytic dismutation reaction, and therefore, EUK-134 is thought to catalyze the dismutation reaction of hydrogen peroxide. HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) and ESP-fitted charge analysis of EUK-134 indicate that Mn atom plays an electron acceptor and donor for dismutation reactions of superoxide radical and hydrogen peroxide catalyzed by EUK-134, respectively. [ABSTRACT FROM AUTHOR]

Zinc ferrite ZnFe 2 O 4 belongs to the spinel-type ferrites that have been proposed as photocatalysts for water splitting. The electronic band gap and the band edge positions are of utmost importance for the efficiency of the photocatalytic processes. We, therefore, calculated the absolute band energies of the most stable surface of ZnFe 2 O 4 , the Zn-terminated (100) surface at self-consistent hybrid density functional theory level. The effect of Fe- and Zn-rich environments, cation exchange as antisite defects and implicit solvation on the band positions is investigated. Calculated flat band potentials of the pristine surface model ranges from - 0.9 to - 0.8 V against SHE in vacuum. For Zn-rich (Fe-rich) models this changes 0.3–0.9 (0.0–0.7) V against SHE. Fe-rich models are closest to the experimental range of reported flat band potentials. Solvent effects lower the calculated flat band potentials by up to 1.8 eV. The calculated band gaps range from 1.5 to 2.9 eV in agreement with previous theoretical work and experiment. Overall, our calculations confirm the experimentally observed low activity of ZnFe 2 O 4 and its dependence on preparation conditions. [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]

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]

Understanding how halogens are distributed among usual hydrous silicates in the lithosphere is important to constrain their deep geochemical cycle and fluid-rock interactions in subduction zones. This article presents first-principles modelling of halogen (F−, Cl−, Br−) incorporation in hydrous silicates including mica, chlorite, serpentine, amphibole, epidote and carpholite. The approach allows studying the impact of crystal chemistry on halogen partitioning by quantification of the energetic cost of halogen incorporation in minerals. Calculations are carried out in large systems where halogens are in minor to trace concentrations. Estimations show that F-bearing defects must be separated at least 9 Å from one another to reproduce trace element behaviour, this value increasing to at least 10 Å for Cl and Br. Results highlight the competition between the effects of electrostatic interactions and steric hindrance for incorporation of halogens, where steric hindrance has greater importance for heavy halogens, in particular for Br. Interaction with alkalis is a major control for F incorporation, especially in mica. Other parameters such as octahedral site occupancy, Si/Al ratio of tetrahedral sites and the nature of alkalis in amphibole and mica (K or Na) appear to play subordinate roles. Partition coefficients have been estimated in mineral assemblages in an effort to be representative of subduction zone metamorphism. Results show that pargasite, biotite and lizardite are favoured hosts for all three halogens, followed by clinochlore, tremolite and carpholite. The energetic cost of incorporating halogens into dioctahedral phyllosilicates and epidote is comparatively higher, and partitioning is predicted as unfavourable to these minerals. Fractionation between halogens in subduction zones is predicted by the evolution of mineral assemblages and partition coefficients, a consequence of the influence of crystal chemistry over halogen incorporation in hydrous silicates. [ABSTRACT FROM AUTHOR]

The photoassociation of alkali metal molecules (Rb2, Cs2, and RbCs) at short range is investigated in theory. Based on ab initio calculations to rationalize Franck–Condon filtering, the target states of photoassociation have been obtained. They correspond to vibrational transition levels from excited state (Rb2: = 17–21, Cs2: = 21–25, and RbCs: = 18–22) to ground state. By using quantum wave-packet dynamic methods, the yields with time evaluation of the selected states are calculated interacting with a resonant laser pulse. Using gaussian pulse leads to the yield of Rb2 up to 82% at 860 fs. After a laser pulse, the positive chirp promotes the yield of vibrational states to increase, but the negative chirp inhibits it. That is to say, by changing the laser parameters and pulse shapes, it is much easier to control the photochemical process along desired direction. For photoassociation of alkali-metal dimers, homonuclear molecules have a better response to laser pulse than heteronuclear molecules. The efficiency of photochemical reaction of homonuclear molecules is much better and the photoassociative yield is much higher. Those conditions will provide an important reference and suggest a scheme for a feasible photoassociation for further experimental and theoretical research. [ABSTRACT FROM AUTHOR]

The kinetics of hydrogen atom abstraction from methyl propionate (MePr), a biodiesel model, by •H and •CH3 radicals, have been studied. Here, we employ density functional theory (BB1K, BMK, M06-2X, M08-HX, and ωB97XD) and ab initio (MP2, CBS-QB3, and G3) calculations. Rate coefficients of each of six-bimolecular reaction pathways of MePr oxidation were calculated using the conventional transition state theory (TST) with Eckart (Eck) tunneling correction over a wide temperature range, 700-1600 K at pressure 1.0 atm. Branching ratios analysis of different reaction channels indicates that abstraction of H atom from Cα is the most dominated route for MePr fuel consumption. However, rate constants of H-atom abstraction from the terminal methyl groups increase with rising of temperature for both •H and •CH3 radicals. [ABSTRACT FROM AUTHOR]

The effect of the addition of rhodium (Rh), rhenium (Re), tungsten (W), gold (Au), and platinum (Pt) on the shear modulus of face-centered cubic iridium (Ir) was investigated using an ab initio method. The shear modulus was calculated using the second derivative of the strain energy with respect to strain. It was found that both the bulk modulus (G) and the ratio (G/B) between bulk and shear modulus decreased with the addition of elements to the Ir, which meant that all five of these alloy elements lowered the brittleness of the bulk Ir. The decreased shear modulus was the main factor for the lowered brittleness. And the decreasing order of shear modulus in the [112] and [100] crystalline directions was Ir > Rh > Pt > W = Au > Re and Ir > W > Rh > Pt > Au > Re respectively. The reason for the order was both the atomic distance and the bond strength between alloy atoms and Ir atoms. The larger bond strength meant the larger shear modulus, and the smaller atomic distance meant the smaller shear modulus. [ABSTRACT FROM AUTHOR]

The Fe-Co-Cr-Ni quaternary system has been studied extensively in the past decade, not only because of the superior properties achieved like high tensile ductility and fracture toughness, but also it is the foundation for the development of FeCrCoNi-based HEAs. However, most of the investigations are mainly focusing on the equiatomic and semi-equiatomic compositions. The physical properties of non-equiatomic compositions are barely explored. In the current work, the ab initio approach is adopted to predict the lattice parameter, structure stabilities, elastic properties, and enthalpy of formations of fcc Fe-Cr-Co-Ni HEA single crystals with the special quasirandom structure (SQS) method. To expand the design of Fe-Co-Cr-Ni HEAs into a full composition range, the current simulations cover all the binaries, ternaries, and the whole quaternary system. The 2-D composition-property contour diagrams are created to show the physical properties in the ternary and quaternary systems. Our investigation shows that the fcc alloys' lattice parameter increases with the addition of Fe and Cr and decreases with Ni and Co. In addition to the enthalpy of formation at 0 K, the shape distortion rate is proposed to be another essential parameter to evaluate the crystal stability. The results show the addition of Cr would destabilize the fcc lattice and cause symmetry breaking. Finally, the result of Pugh's ratio shows that most of the fcc alloys show ductile behavior ( P > 1.75), especially for the alloys around Fe3Ni, FeCo, and Fe2NiCo ( P > 2.5). The brittle behavior ( P < 1.75) is located around Fe3Cr and Fe2CoCr. Meanwhile, Cr2NiCo and Cr2FeNiCo are considered promising compositions to be tried and verified experimentally because of the higher bulk modulus and moderate shear modulus. [ABSTRACT FROM AUTHOR]

The relevance of a selection of organic impurities for the initiation of the MTO process was quantified in a kinetic model comprising 107 elementary steps with ab initio computed reaction barriers (MP2:DFT). This model includes a representative part of the autocatalytic olefin cycle as well as a direct initiation mechanism starting from methanol through CO-mediated direct C–C bond formation. We find that the effect of different impurities on the olefin evolution varies with the type of impurity and their partial pressures. The reactivity of the considered impurities for initiating the olefin cycle increases in the order formaldehyde < di-methoxy methane < CO < methyl acetate < ethanol < ethene < propene. In our kinetic model, already extremely low quantities of impurities such as ethanol lead to faster initiation than through direct C–C bond formation which only matters in complete absence of impurities. [ABSTRACT FROM AUTHOR]

Unimolecular pyrolysis of isopropyl acetate (IPA) and isopropyl propanoate (IPP) esters as biodiesel surrogates has been carried out using density functional theory (DFT) at BMK/DZ, TZ level and CBS-QB3 ab initio calculations. Results were compared with isopropyl butanoate (IPB). The rate constants for unimolecular decomposition reactions are calculated based on transition state theory (TST) and compared with the available experimental data. Derived reaction rates have been calculated at a wide range of temperatures relevant to the interest of atmospheric and combustion communities. Among all dissociation channels of IPA, IPP and IPB, acid/propene formation is the most favorable reaction path from kinetic and thermodynamic points of view. On the other side, formation of lower esters is obstructed by high activation energy barriers and is improbable to occur except at high temperature for IPP and IPB. Reaction channels involving simple bond scission require less energy than new esters formation. [ABSTRACT FROM AUTHOR]

In the present work, the influence of hybridization on cooperativity between C–H···N hydrogen bonds is theoretically investigated. Here, C2H6, C2H4, and C2H2 are considered as hydrogen bonding donor while NH3, N2H4, N2H2, and N2 act as the hydrogen bonding acceptor. The calculations are performed at MP2/aug-cc-pVTZ level. It is observed that the stability of systems is amplified as C(sp) > C(sp2) > C(sp3) and also N(sp3) > N(sp2) > N(sp). The role of interaction and deformation energies on the stability of the systems is examined. The results indicate the contribution of interaction energy is dominant in all complexes. The strength of C–H···N hydrogen bond is estimated using interaction energy. In agreement with cooperative energies, the C–H···N hydrogen bond is respectively weakened/strengthened in the triads containing C(sp) and C(sp2)/C(sp3) where two hydrogen bonds coexist. On the other hand, the C–H···N hydrogen bond is strengthened in the ternary systems including N(sp3) and N(sp2) while an opposite behavior is obtained in the triad having N(sp). [ABSTRACT FROM AUTHOR]

Dried duckweed-Lm aquatic plant was subjected to molecular modifications using quantum mechanical calculations. The molecular modeling simulates aquatic weed as a composite of cellulose/lignin/glycine. This model suggests the ability to remove inorganic pollutants from wastewater according to unique hydrogen bonding and high total dipole moment. For verifications, experimental efforts are performed for the phytoremediation of Cr (VI) from aqueous solution using a species of Duckweed Lemna minor (Lm) through adsorption process. Duckweed-Lm biomass was prepared and characterized by X-ray diffraction (XRD), scan electron microscope (SEM), Fourier-transform infrared (FTIR) and Brunauer– Emmett–Teller (BET). The effect of several important parameters, such as pH, sorbent dose, contact time, temperature, sorption and desorption processes, was studied. The phytoremediation of Cr(VI) ion was found to be pH-dependent with a maximum removal of 64% achieved at pH of 3.8 and a lowest removal of 25% at pH of 9.5. The obtained adsorption results indicated that duckweed-Lm can be effective for chromium ion removal from aqueous solutions. [ABSTRACT FROM AUTHOR]

The structural, optoelectronic, and thermoelectric properties of CaTe, Ca0.5Ba0.5Te, CaTe0.5Se0.5, and Ca0.5Ba0.5Te0.5Se0.5 alloys are studied using the full-potential linearized augmented plane wave method within the framework of density functional theory. The calculated ground-state properties agree well with available data. The electronic and bonding behavior of the materials is studied and further verified by electron density contours. Additionally, mechanical stability is confirmed by calculating the shear modulus, Young's modulus, bulk modulus, and hardness values. From the brittle/ductile analysis, the newly predicted compounds are found to be less brittle (more ductile) than the parent CaTe compound. The valence band maxima and the conduction band minima (CBM) of the Ca0.5Ba0.5Te, CaTe0.5Se0.5, and Ca0.5Ba0.5Te0.5Se0.5 alloys are located at the Г point, resulting in a direct bandgap. The optical properties of the materials are calculated for the energy range of 0–13.5 eV. As expected, the highest Seebeck coefficient value is observed as 245.8 μV/K and 248.6 μV/K for CaTe0.5Se0.5 and Ca0.5Ba0.5Te0.5Se0.5 alloys, respectively, at 300 K. The present work exhibits the optoelectronic and thermoelectric properties, but the available material flexibility has various other applications. [ABSTRACT FROM AUTHOR]

Using density functional theory calculations within the generalized gradient approximation, the electronic density of states and band structure of NdMnO 3 simple perovskite are analyzed. It is found that the compound behaves as a ferromagnetic half-metal material. By using Monte Carlo simulations within the framework of the Ising model, the effects of the crystal field and the exchange interaction between the magnetic atoms Mn–Mn and Nd–Mn on the magnetization, susceptibility, specific heat, and internal energy are investigated. The magnetocaloric effect of NdMnO 3 is also examined. It is observed that the relative cooling power (RCP) increases when the applied magnetic field or Mn–Mn exchange interaction is increased, whereas the RCP decreases when the crystal field or Nd–Mn exchange interaction is increased. These results show that NdMnO 3 is a potential candidate for use in magnetic refrigeration and spintronic applications. [ABSTRACT FROM AUTHOR]

The O–H bond strength was calculated by the G4 and the M06-2X/MG3S methods for 2‑hydroxy-3-methylcyclopent-2-en-1-one (maple lactone), 4-hydroxy-2,3-dimethyl-2H-furan-5-one (sotolon), 4-hydroxy-5-methylfuran-3-one, 4-hydroxy-2,5-dimethylfuran-3-one (strawberry furanone), (2R)-2-[(1S)-1,2-dihydroxyethyl]-3,4-dihydroxy-2H-furan-5-one (ascorbic acid), 5-hydroxy-2-(hydroxymethyl)pyran-4-one (kojic acid), 3-hydroxy-2-methylpyran-4-one (maltol), 3-hydroxy-2-ethylpyran-4-one (ethylmaltol), 4-hydroxy-6-methylpyran-2-one, and 5-hydroxy-6-methyl-3,4-dihydro-2H-pyran-4-one (dihydromaltol). The calculations indicated the presence of a weak O–H bond of less than 82.0 kcal/mol in 4-hydroxyfuran-3-one derivatives. The experimental rate constant of the reaction of the compound with the lowest O–H bond strength, 4-hydroxy-2,5-dimethylfuran-3-one, with peroxyl radicals in chlorobenzene and acetonitrile was comparable to the data for dibutylhydroxytoluene, but the stoichiometric coefficient of inhibition was 0.17 (PhCl) and 0.66 (MeCN), which was significantly smaller than for dibutylhydroxytoluene. The activation enthalpy for hydrogen atom elimination from 4-hydroxy-2,5-dimethylfuran-3-one by peroxyl radicals calculated by the SMD(PhCl)-M05/MG3S method correlated well with the data for 5-hydroxy and 5-aminouracil derivatives, which is indicative of the common mechanism of interaction of these compounds with peroxyl radicals. [ABSTRACT FROM AUTHOR]

Monoclinic lithium vanadium phosphate Li3V2(PO4)3 is a very promising cathode candidate for applications in Li-ion batteries, with a high operational voltage (~ 4 V vs. Li+/Li) and a high theoretical capacity of 197 mAh/g. However, the underlying electrochemical mechanism of monoclinic Li3V2(PO4)3 is not yet fully understood, due to its complexity. To gain more knowledge about the electrochemical performance of the monoclinic Li3V2(PO4)3, we perform density functional calculations of structural, electrochemical, electronic, and magnetic properties of LixV2(PO4)3 for x = 3, 2, 1, based on the full-potential linearized augmented plane wave (FP-LAPW) method. The generalized gradient approximation corrected with the present work self-consistently calculated Hubbard parameter U (GGA+U method) shows that it can successfully reproduce the experimental average lithium intercalation voltage for the redox couple V4+/V3+ within 7% error, and within 2% error for the transition x: 3 ➔ 2. The present work method is fully ab initio and without any arbitrary parameters. In the literature, the existence of charge ordering in Li2V2(PO4)3 is subject to discrepancy. By analyzing the present calculated structural, magnetic, and electronic properties of Li2V2(PO4)3, the existence of charge ordering had been confirmed. The present work method sets the path for accurately predicting the redox potential of future lithium and sodium phosphate compounds for the next-generation batteries technology. [ABSTRACT FROM AUTHOR]

The energies, structures, and vibrational frequencies of M(H2O)n, M = Tl3+, Hg2+, n = 0–9, 18 have been calculated at 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. The metal–oxygen distances and totally symmetric stretching frequency of the aqua ions were compared with each other and with solution measurements. The results are consistent with thallium(III) and mercury(II) being hexacoordinate in aqueous solution. The use of symmetry is shown to be advantageous. [ABSTRACT FROM AUTHOR]

We present a joint experimental and computational terahertz (THz) spectroscopy study of the most stable polymorph (form I) of an antihypertensive pharmaceutical solid, felodipine (FLD). The vibrational response has been analyzed at room temperature by combining optical (THz-TDS, FT-IR, THz-Raman) and neutron (INS) terahertz spectroscopy. With the challenging example of a large and flexible molecular solid, we illustrate the complementarity of the experimental techniques. We show how the results can be understood by employing ab initio modeling and discuss current progress in the field. To this end, we employ plane wave formulation of density functional theory (plane wave DFT) along with harmonic lattice dynamics calculations (HLD) and ab initio molecular dynamics (AIMD) simulations. Based on a comprehensive theoretical analysis, we discover an inconsistency in the commonly accepted structural model, which can be linked to a distinct librational dynamics of the side ester chains. As a result, only a moderate agreement with the experimental spectra can be achieved. We, therefore, propose an alternative structural model, effectively accounting for the influence of the large-amplitude librations and allowing for a comprehensive analysis of the vibrational resonances up to 4.5 THz. In that way, we illustrate the applicability of the computationally supported THz spectroscopy to detect subtle structural issues in molecular solids. While the provided structural model can be treated as a guess, the problem calls for further revision by means of high-resolution crystallography. The problem also draws a need of extending the THz experiments toward low-temperature conditions and single-crystal samples. On the other hand, the studied system emerges as a challenge for the DFT modeling, being extremely sensitive to the level of the theory used and the resulting description of the intermolecular forces. FLD form I can be, hence, considered as a testbed for the use of more sophisticated theoretical approaches, particularly relying on an advanced treatment of the van der Walls forces and going beyond zero-temperature conditions and harmonic approximation. [ABSTRACT FROM AUTHOR]

The effects of the stereoelectronic interaction on the structural and conformational properties of fluoromethyl methyl ether (1) and its analogues containing Cl (2), Br (3), and I (4) atoms were investigated by means of hybrid-density functional based method (B3LYP/Def2-TZVPP) and natural bond orbital (NBO) interpretation. Consistent with the reported experimental data, the chiral gauche conformations of compounds 1–4 are more stable than their corresponding anti conformations. The results showed that the energy barriers of the racemization processes of the chiral gauche-conformations of compounds 1–4 via the plane symmetrical anti conformations are smaller than the plane symmetrical eclipsed transition structures. According to the NBO analysis, the hyperconjugative generalized anomeric effect (HCGAE) increased from compound 1 to compound 4, which explains the increase of the energy discrepancy between their corresponding chiral gauche- and plane symmetrical anti-conformations. In contrast to the trend for the HCGAE, the determined dipole moment discrepancy between the chiral gauche- and plane symmetrical anti-conformations (µanti–µgauche) reduced from compound 1 to compound 4. This fact reveals that there is no correlation between the variations of the conformational preferences in compounds 1–4 and the electrostatic effects associated with the dipole–dipole interactions. There is an excellent agreement between the racemization energy barriers and the proportion between the GAE for compounds 2–4 and compound 1 (i.e., GAEx/GAE1) as well as the difference between the Wiberg Bond Indexes of C1–O2 bonds (Δ[WBIanti-gauche(C1–O2)]). The associations between the HCGAE, pairwise steric exchange energies (PSEE), WBI, dipole moments, orbital integrals, structural parameters, and conformational behaviors of compounds 1–4 have been studied. [ABSTRACT FROM AUTHOR]

The properties of the hydrogen-bonded complexes of chloroform and bromoform with ammonia, water, hydrogen fluoride, phosphine, hydrogen sulphide and hydrogen chloride were studied by means of ab initio calculations. The properties of interest were the molecular structures, the interaction energies, the vibrational spectra and the nature of the orbital interactions involved in the formation of the complexes. Of particular interest was the determination of whether the various interactions exhibited red-shifted or blue-shifted hydrogen bond behaviour. The complexes optimized in three distinct structural models, singly bonded, cyclic and cage. The interaction energies, in the main, varied systematically with changes of the haloform and of the partner molecules. Changes of the CH or YH (Y = N, O, F, P, S and Cl) bond lengths correlated in most cases with the interaction energies, subject to some inconsistencies, with opposite behaviour being shown by the two sets. Similarly, the CH and YH stretching wavenumber shifts also displayed a dependence on the interaction energies, tracking with the bond length changes. Based on the diagnostic utility of these structural and spectroscopic properties, the complexes were found to be almost exclusively red-shifted, for binding through both the CH and YH groups. The orbital interactions responsible for the stability of the complexes were determined to be donation from a Y atom lone pair orbital of the partner molecule to a CH σ antibonding orbital and from a X lone pair orbital (X = Cl and Br) of the haloform to a YH σ antibonding orbital. [ABSTRACT FROM AUTHOR]

Peroxides play a central role in many chemical and biological processes such as the Fenton reaction. The relevance of these compounds lies in the low stability of the O–O bond which upon dissociation results in radical species able to initiate various chemical or biological processes. In this work, a set of 64 DFT functional-basis set combinations has been validated in terms of their capability to describe bond dissociation energies (BDE) for the O–O bond in a database of 14 ROOH peroxides for which experimental values of BDE are available. Moreover, the electronic contributions to the BDE were obtained for four of the peroxides and the anion H 2 O 2 - at the CBS limit at CCSD(T) level with Dunning's basis sets up to triple- ζ quality providing a reference value for the hydrogen peroxide anion as a model. Almost all the functionals considered here yielded mean absolute deviations around 5.0 kcal mol - 1 . The smallest values were observed for the ω B97 family and the Minnesota M11 functional with a marked basis set dependence. Despite the mean deviation, order relations among BDE experimental values of peroxides were also considered. The ω B97 family was able to reproduce the relations correctly whereas other functionals presented a marked dependence on the chemical nature of the R group. Interestingly, M11 functional did not show a very good agreement with the established order despite its good performance in the mean error. The obtained results support the use of similar validation strategies for proper prediction of BDE or other molecular properties by DFT methods in subsequent related studies. [ABSTRACT FROM AUTHOR]

In this study, the pKa value of the phenylpropanolamine, dissolved in water, was theoretically calculated at T = 298.15, 303.15, 308.15, 313.15, 318.15, and 323.15 K using ab initio and DFT methods with B3LYP/6-31+G(d) level of theory basis set. Tomasi's method was used to study on the hydrogen bonds (IHB,s) between various species of phenylpropanolamine and water molecule. Some structural properties such as total atomic charge, au, the bond lengths between the indicated atoms, d, the angles between the indicated atoms, A, and the dihedral angle between the indicated atoms, D, were calculated for phenylpropanolamine in water at constant temperature. In addition, the changes in entropy (ΔS) and enthalpy (ΔH) were obtained for deprotonation process of phenylpropanolamine in water. In this research work, we showed that there is a good agreement between the experimentally determined and theoretically calculated pKa of the phenylpropanolamine, in water, at T = 298.15 K. [ABSTRACT FROM AUTHOR]

Calculations using the density-functional theory (DFT) in combination with the single defect method were carried out to determine the heat of mixing behaviour of mineral solid solution phases. The accuracy of this method was tested on the halite–sylvite (NaCl–KCl) binary, pyrope–grossular garnets (Mg3Al2Si3O12–Ca3Al2Si3O12), MgO–CaO (halite structure) binary, and on Al/Si ordered alkali feldspars (NaAlSi3O8–KAlSi3O8); as members for coupled substitutions, the diopside–jadeite pyroxenes (CaMgSi2O6–NaAlSi2O6) and diopside–CaTs pyroxenes (CaMgSi2O6–CaAlAlSiO6) were chosen for testing and, as an application, the heat of mixing of the tremolite–glaucophane amphiboles (Ca2Mg5Si8O22(OH)2–Na2Mg3Al2Si8O22(OH)2) was computed. Six of these binaries were selected because of their experimentally well-known thermodynamic mixing behaviours. The comparison of the calculated heat of mixing data with calorimetric data showed good agreement for halite–sylvite, pyrope–grossular, and diopside–jadeite binaries and small differences for the Al/Si ordered alkali feldspar solid solution. In the case of the diopside–CaTs binary, the situation is more complex because CaTs is an endmember with disordered cation distributions. Good agreement with the experimental data could be, however, achieved assuming a reasonable disordered state. The calculated data for the Al/Si ordered alkali feldspars were applied to phase equilibrium calculations, i.e. calculating the Al/Si ordered alkali feldspar solvus. This solvus was then compared to the experimentally determined solvus finding good agreement. The solvus of the MgO–CaO binary was also constructed from DFT-based data and compared to the experimentally determined solvus, and the two were also in good agreement. Another application was the determination of the solvus in tremolite–glaucophane amphiboles (Ca2Mg5Si8O22(OH)2–Na2Mg3Al2Si8O22(OH)2). It was compared to solvi based on coexisting amphiboles found in eclogites and phase equilibrium experiments. [ABSTRACT FROM AUTHOR]