Density Functional Theory Studies on the Adsorption of NH2NO2 on Al13 Cluster

Density functional theory method with full geometry optimization was used to study the adsorption of nitroamine (NH₂NO₂) on Al₁₃ cluster. Both dissociative and nondissociative adsorption structures were predicted with different NH₂NO₂ molecule orientations on Al₁₃ cluster surfaces. In dissociative chemisorption, the main decomposition products of NH₂NO₂ are O atom(s) and NH₂NO or NH₂N species. The O atoms being ruptured from the N?CO bond form strong Al?CO bonds with the neighboring Al around the adsorbed sites. In addition, the species obtained as a result of O atom elimination remains bonded to the surface. The largest adsorption energy is ?737.66?kJ/mol when the NH₂NO₂ molecule decomposes into two O atoms and a NH₂N fragment. For nondissociative adsorption, the seriously deformed nitroamine forms various N?CO?CAl bonding configurations with Al. The significant charge transfer occurs for all adsorption configurations. The most charge transfer is 2.068 e from the Al cluster surface to the fragments of the decomposed NH₂NO₂. The change of the electronic structures is obvious due to the adsorption or dissociation of NH₂NO₂ molecule. Nitroamine readily oxidizes the aluminum surface of the Al₁₃ cluster.     

Ab initio studies of isomerization and dissociation reactions of methyl peroxynitrate

Using the CCSD(T)/cc-pVDZ//B3LYP/6-311G(2d,2p) method, we calculated the detailed potential energy surfaces (PESs) for the unimolecular isomerization and decomposition of methyl peroxynitrate (CH₃O₂NO₂). The results show that there are the two most stable isomers, IS1a and IS1b, which are a pair of mirror image isomers. From IS1a and IS1b, different isomerization and unimolecular decomposition reaction channels have been studied and discussed. Among them, the predominant thermal decomposition pathways are those leading to CH₃O₂ + NO₂ and cis-CH₃ONO + O₂. The former is the lowest-energy path through the direct O–N bond rupture in IS1a or IS1b. The PES along the O–N bond in IS1a has been scanned, where the energy of IS1a reaches maximum value of 23.5 kcal/mol when the O–N bond is stretched to about 2.8 Å. This energy is 2.7 kcal/mol larger than the O–N bond dissociation energy (BDE) and 2.8 kcal/mol larger than the experimental active energy. In addition, because the energy barriers of IS1a isomerization to IS2a are 23.8 kcal/mol, close to the 20.8 kcal/mol O–N BDE in IS1a or IS1b, the isomerization reaction may compete with the direct bond rupture dissociation reaction.     

Adsorption and Decomposition Mechanism of 1,1‐Diamino‐2,2‐dinitroethylene on Al(111) Surface by Periodic DFT Calculations

The adsorption of 1,1‐diamino‐2,2‐dinitroethylene (FOX‐7) molecule on the Al(111) surface was investigated by the generalized gradient approximation (GGA) of density functional theory (DFT). The calculations employ a supercell (4×4×2) slab model and three‐dimensional periodic boundary conditions. The strong attractive forces between oxygen and aluminum atoms induce the N? O bond breaking of the FOX‐7. Subsequently, the dissociated oxygen atoms and radical fragment of FOX‐7 oxidize the Al surface. The largest adsorption energy is ?940.5 kJ/mol. Most of charge transfer is 3.31e from the Al surface to the fragment of FOX‐7 molecule. We also investigated the adsorption and decomposition mechanism of FOX‐7 molecule on the Al(111) surface. The activation energy for the dissociation steps of P2 con?guration is as large as 428.8 kJ/mol, while activation energies of other con?gurations are much smaller, in range of 2.4 to 147.7 kJ/mol.     

Adsorption and decomposition of HMX and CL‐20 on Al(111) surface by DFT investigation

The adsorption and decomposition of HMX and CL‐20 molecules on the Al(111) surface were investigated by the generalized gradient approximation of density functional theory. The calculations employed a supercell (6 × 6 × 3) slab model and three‐dimensional periodic boundary conditions. The strong attractive forces between HMX (or CL‐20) molecule and Al atoms induce the breaking of N‐O and N‐N bonds in nitro group. Subsequently, the dissociated oxygen atoms, NO₂ groups, and radical fragments of HMX or CL‐20 oxidize the Al surface. The largest adsorption energy is ?1792.7 kJ/mol in B1, where CL‐20 decomposes into four O atoms and a CL‐20 fragment. With the number of the radical species in adsorption configurations increases, the corresponding adsorption energy increases greatly. We also investigated the decomposition mechanism of HMX and CL‐20 molecules on the Al(111) surface. The activation energies (E _a) for the dissociations A2, A3, B1, and B6 are 31.2, 47.9, 75.5, and 75.9 kJ/mol, respectively. Although CL‐20 is more sensitive than HMX in its gaseous state, the E _a of CL‐20 is higher than that of HMX when they adsorb and decompose on the Al(111) surface, which indicates that the HMX is even easier to decompose on Al(111) surface as compared with CL‐20. Copyright © 2016 John Wiley & Sons, Ltd.     

Theoretical mechanistic study on the radical-molecule reaction of CH2Br/CHBrCl with NO2

The radical-molecule reaction mechanisms of CH₂Br and CHBrCl with NO₂ have been explored theoretically at the UB3LYP/6-311G(d, p) level. The single-point energies were calculated using UCCSD(T) and UQCISD(T) methods. The results show that the title reactions are more favorable on the singlet potential energy surface than on the triplet one. For the singlet potential energy surface of CH₂Br + NO₂ reaction, the association of CH₂Br with NO₂ is found to be a barrierless carbon-to-oxygen attack forming the adduct IM1 (H₂BrCONO-trans), which can isomerize to IM2 (H₂BrCNO₂), and IM3 (H₂BrCONO-cis), respectively. The most feasible pathway is the 1, 3-Br shift with C–Br and O–N bonds cleavage along with the N–Br bond formation of IM1 lead to the product P1 (CH₂O + BrNO) which can further dissociate to give P4 (CH₂O + Br + NO). The competitive pathway is the 1, 3-H-shift associated with O–N bond rupture of IM1 to form P2 (CHBrO + HNO). For the singlet potential energy surface of CHBrCl + NO₂ reaction, there are three important reaction pathways, all of which may have comparable contribution to the reaction of CHBrCl with NO₂. The theoretically obtained major products CH₂O and CHClO for CH₂Br + NO₂ and CHBrCl + NO₂ reactions, respectively, are in good agreement with the kinetic detection in experiment.     

Structure and energetic properties of 1,5-dinitrobiuret

The two-dimensional potential energy scan shows that the pseudo-trans conformer of 1,5-dinitrobiuret (DNB) is the most stable form of isolated molecule, while the pseudo-cis conformer is about 7.5 kJ/mol higher in energy. Thus, the structure of gaseous DNB is different from that in crystal state, where the molecules have pseudo-cis conformation. The value of enthalpy of formation of gaseous DNB (?257 ± 5 kJ/mol) is calculated from isodesmic reactions using G4 energies. Combining this value with empirically estimated enthalpy of sublimation, the enthalpy of formation of crystal DNB is predicted to be ?415 ± 15 kJ/mol. The bond dissociation enthalpies are calculated for all bonds. The energy of the weakest N–NO₂ bonds is equal to 190–200 kJ/mol. Similar calculations were carried out for biuret. The gaseous biuret exists predominantly in the pseudo-trans form. The calculated enthalpy of formation of gaseous biuret agrees well with the experimental one. The correlation of calculated bond energies with corresponding bond distances and electron density is discussed for biuret and DNB.     

A theoretical study on the structure and hygroscopicity of ammonium dinitramide

Density functional theory (DFT) and the dispersion corrected DFT have been used to investigate the hygroscopicity of ammonium dinitramide (ADN). Calculation results show that the gaseous ADN has a strong hydrogen bond. But the ionic pair structure NH₄ ⁺ · N(NO₂)^? is stabilized upon the addition of water molecules. Natural bond orbital calculations suggest that the intra- and intermolecular orbital interactions LP(O) → σ*(N–H) or LP(O) → σ*(O–H) make the system stabilized as a whole. En energy decomposition analysis reveals that the interactions between ADN and H₂O are dominated by the electrostatic and orbital interactions. The formation reactions become more spontaneous with the increasing number of water molecules but can be weakened by the growing temperature from 200 to 400 K. Moreover, the molecular dynamic method is applied to explore a more realistic cluster model to study the interactions between ADN and H₂O.     

Density-functional study for the NOx (x = 1, 2) dissociation mechanism on the Cu(1 1 1) surface

Spin-polarized density functional theory calculation is employed to study the adsorption and dissociation of NO₂ molecule on Cu(1 1 1) surface. It is shown that the most favorable adsorption structure is the NO₂ (T,T-O-,O′-nitrito) configuration which has an adsorption energy of −1.49 eV. The barriers for step-wise NO₂ dissociation reaction, NO_2(g) → N_(a) + 2O_(a), are 1.05 (for O–N–O bond activation), and 2.08 eV (for N–O bond activation), respectively, and the entire process is 0.6 eV exothermic. The energetics of single N–O dissociation with and without the presence of N atom or O atom on the surface are also calculated. The results indicate that in the presence of O atom on Cu(1 1 1) surface would raise the N–O dissociation barrier, whereas in the presence of N atom decrease it. The interaction nature between adsorbates and substrate is analyzed by the local density of states (LDOS) calculation.     

DFT quantum-chemical calculations of nitrogen oxide chemisorption and reactivity on the Cu(100) surface

A DFT quantum-chemical study of NO adsorption and reactivity on the Cu₂₀ and Cu₁₆ metal clusters showed that only the molecular form of NO is stabilized on the copper surface. The heat of monomolecular adsorption was calculated to be ΔH _m = ?49.9 kJ/mol, while dissociative adsorption of NO is energetically unfavorable, ΔH _d = + 15.7 kJ/mol, and dissociation demands a very high activation energy, E _a = + 125.4 kJ/mol. Because of the absence of NO dissociation on the copper surface, the formation mechanism of the reduction products, N₂ and N₂O, is debatable since the surface reaction ultimately leads to N-O bond cleavage. As the reaction occurs with a very low activation energy, E _a = 7.3 kJ/mol, interpretation of the NO direct reduction mechanism is both an important and intriguing problem because the binding energy in the NO molecule is high (630 kJ/mol) and the experimental studies revealed only physically adsorbed forms on the copper surface. It was found that the formation mechanism of the N₂ and N₂O reduction products involves formation (on the copper surface) of the (O_adN-NO_ad) dimer intermediate that is chemisorbed via the oxygen atoms and characterized by a stable N-N bond (r _N-N ～1.3 Å). The N-N binding between the adsorbed NO molecules occurs through electron-accepting interaction between the oxygen atoms in NO and the metal atoms on the “defective” copper surface. The electronic structure of the (O_adN-NO_ad) surface dimer is characterized by excess electron density (ON-NO)^δ? and high reactivity in N-O_ad bond dissociation. The calculated activation energy of the destruction of the chemisorbed intermediate (O_adN-NO_ad) is very low (E _a = 5–10 kJ/mol), which shows that it is kinetically unstable against the instantaneous release of the N₂ and N₂O reduction products into the gas phase and cannot be identified by modern experimental methods of metal surface studies. At the same time, on the MgO surface and in the individual (Ph₃P)₂Pt(O₂N₂) complex, a stable (O_adN-NO_ad) dimer was revealed experimentally.     

Characterization of <Emphasis Type="Italic">σ</Emphasis>-hole interactions in 1:1 and 1:2 complexes of YOF<Subscript>2</Subscript>X (X = F,Cl, Br,I; Y = P,As) with ammonia: competition between halogen and pnicogen bonds

Ab initio calculations at the MP2/aug-cc-pVTZ level of theory are performed to examine 1:1 and 1:2 complexes of YOF₂X (X = F, Cl, Br, I; Y = P, As) with ammonia. The YOF₂X:NH₃ complexes are formed through the interaction of the lone pair of the ammonia with the σ-hole region associated with the X or Y atom of YOF₂X molecule. The calculated interaction energies of halogen-bonded complexes are between ?1.06 kcal/mol in the POF₃···NH₃ and ?6.21 kcal/mol in the AsOF₂I···NH₃ one. For a given Y atom, the largest pnicogen bond interaction energy is found for the YOF₃, while the smallest for the YOF₂I one. Almost a strong linear relationship is evident between the interaction energies and the magnitudes of the positive electrostatic potentials on the X and Y atoms. The results indicate that the interaction energies of halogen and pnicogen bonds in the ternary H₃N:YOF₂X:NH₃ systems are less negative relative to the respective binary systems. The interaction energy of Y···N bond is decreased by 1–22 %, whereas that of X···N bond by about 5–61 %. That is, both Y···N and X···N interactions exhibit anticooperativity or diminutive effects in the ternary complexes.     

Comparative theoretical studies of substituted bridged bipyridines and their N-oxides

In this work, the experimental synthesized bipyridines azo-bis(2-pyridine),4,4′-dimethyl-3,3′-dinitro-2,2′-azobipyridine, and N,N′-bis(3-nitro-2-pyridinyl)-methane-diamine and a set of designed bipyridines that have similar frameworks but different linkages and substituents were studied theoretically at the B3LYP/6-31G* level of density functional theory. The gas-phase heats of formation were predicted based on the isodesmic reactions, and the condensed-phase heats of formation and heats of sublimation were estimated in the framework of the Politzer approach. The crystal densities have been computed from molecular packing and results show that incorporation of –N=N–, –N=N(O)–, –CH=N–, and –NH–NH– into bipyridines is more favorable than –CH=CH– and –NH–CH₂–NH– for increasing the density. The predicted detonation velocities (D) and detonation pressures (P) indicate that –NH₂, –NO₂, and –NF₂ can enhance the detonation performance, and –NO₂ and –NF₂ are more favorable. Introducing –N=N–, –N=N(O)–, and –NH–NH– bridge groups into bipyridines is also favorable for improving their detonation performance. The oxidation of pyridine N always but that of –N=N– bridge does not always improve the detonation properties. E4–O, the derivative with –N=N– bridge and two –NF₂ substituent groups, has the largest D (9.90 km/s) and P (47.47 GPa). An analysis of the bond dissociation energies shows that all derivatives have good thermal stability.     

Molecular structure and relative stability of trans and cis isomers of formanilide: gas-phase electron diffraction and quantum chemical studies

Molecular structure of formanilide is determined by gas-phase electron diffraction (GED) augmented by quantum chemical calculations (B3LYP/cc-pVTZ and MP2/cc-pVTZ) and literature microwave (MW) data. The combined GED and MW data are well reproduced for the mixture of trans and cis isomers with the relative abundance of 59 ± 5 and 41 ± 5 %, respectively, at T = 410 K. The trans isomer (C _s symmetry) is planar, while the cis isomer (C ₁ symmetry) has the twisted structure with the amide group rotated by 36.7 ± 2.7° with respect to the phenyl ring. In accord with theoretical calculations, the amide bond –NH–C(O)– is planar in trans formanilide and a somewhat nonplanar in cis isomer. Accurate structural parameters were obtained by a simultaneous fit of the rotational constants reported in the literature and GED intensities obtained in this study. The N–C(O) and N–C_Ph bond dissociation energies in formanilide are calculated using Gaussian-4 method. It is revealed that the strength of N–C(O) bond in formanilide is 50 kJ/mol less than that in benzamide. On the contrary, the strength of adjacent bond (N–C_Ph) increases by 35 kJ/mol compared to aniline. It is rather unexpectedly that the bond strength weakening does not result in the bond elongating, and vice versa.     

Thermal behaviour of <Emphasis Type="Italic">sym</Emphasis>-octahydroacridines and their corresponding N(10)-oxides

We present and discuss results on the thermal behaviour of 1,2,3,4,5,6,7,8-octahydroacridine (OHA), together with six 9-substituted congeners, i.e. R = –Br, –OCH₃, –NH₂, –NO₂, –OH, and furyl (–C₄H₃O), and their corresponding N(10)-oxides, under nitrogen atmosphere and with alumina as reference, at a heating rate of 5 °C min^?1 from room temperature to 300 °C. Chromatography has been carried out on aluminium sheets, with aluminium oxide 60 F254 neutral (Merck). Melting effects are observed for almost all compounds in their corresponding curves, precisely determined by using a Boetius apparatus. Homolysis of the carbon-substituent bond occurs in most cases, a phenomenon which is consistent with the values of the bond dissociation energy. For all compounds, except for hydroxyl congeners, thermal decomposition started with an endothermic peak. Octahydroacridines readily decompose into volatile products, an effect which correlates with their low melting points, while little amounts of residue remain in place of the aromatic amines compared to the N(10)-oxides. The presence of N–O bonds greatly influences the thermal stability of the compound, in the sense of increasing it compared with the parent amine. Quantitative studies of the decomposition products reveal that the melting points, the 9-position substituent, and N–O bond all play an important role upon the thermal behaviour. Mechanistic/kinetic pathways are also proposed as such results are important in further designing laser processing protocols, i.e. matrix-assisted pulsed laser evaporation (MAPLE) or laser-induced forward transfer (LIFT), for thin film deposition and/or device printing.     

Molecular structure and binding energies of monosubstituted hexacarbonyls of chromium,molybdenum, and tungsten: Relativistic density functional study

Relativistic density functional calculations have been carried out for the group VI transition metal carbonyls M(CO)₅L (M=Cr, Mo, W; L=OH₂, NH₃, PH₃, PMe₃, N₂, CO, OC (isocarbonyl), CS, CH₂, CF₂, CCl₂, NO⁺). The optimized molecular structures and M(SINGLE BOND)L bond dissociation energies, as well as the metal–carbonyl bond energy of the trans CO group, have been calculated. Besides the marked dependence of the trans M(SINGLE BOND)CO bond length on the type of ligand L, such an effect on the that bond energy is also observed. For the chromium compounds, the trans Cr(SINGLE BOND)CO bond length varies from 184 to 199 pm and its bond energy from 242 to 150 kJ/mol. For the molybdenum compounds, the range is 197 to 216 pm and 253 to 128 kJ/mol and, for tungsten, 198 to 214 pm and 293 to 159 kJ/mol. The observed trends can be explained with the π acceptor strength of the L ligand. © 1997 John Wiley & Sons, Inc. J Comput Chem 18 : 1985–1992, 1997     

First principle study of hydrogen storage on the graphene-like aluminum nitride nanosheet

Employing density functional calculations including an empirical dispersion term, we investigated the hydrogenation of an aluminum nitride nanosheet (h-AlN) with atomic and molecular hydrogen. It was found that atomic H prefers to be adsorbed on an N atom rather than Al, releasing energy of 21.1 kcal/mol. The HOMO/LUMO energy gap of the sheet is dramatically reduced from 107.9 to 44.5 kcal/mol, upon the adsorption of one hydrogen atom. The adsorption of atomic H on the h-AlN presents properties which are promising for nanoelectronic applications. The molecular H₂ was found to be adsorbed collinearly on an N atom and dissociated to two H atoms on Al–N bond. Calculated barrier and adsorption energies for this dissociation process are about +18.9 and ?1.9 kcal/mol. We predict that each nitrogen atom in an AlN sheet can adsorb two hydrogen molecules on opposite sides of the sheet, and thus the gravimetric density for hydrogen storage on AlN sheet is evaluated to be about 8.9 wt%.     

Theoretical calculation of nitro-1-(2,4,6-trinitrophenyl)-1H-azoles energetic compounds

In order to study the properties of new energetic compounds formed by introducing nitroazoles into 2,4,6-trinitrobezene, the density, heat of formation and detonation properties of 36 nitro-1-(2,4,6-trinitrobenzene)-1H-azoles energetic compounds are studied by density functional theory, and their stability and melting point are predicted. The results show that most of target compounds have good detonation properties and stability. And it is found that nitro-1-(2,4,6-Trinitrophenyl)-1H-pyrrole compounds and nitro-1-(2,4,6-trinitrop-enyl)-1H-Imidazole compounds have good thermal stability, and their weakest bond is C NO₂ bond, the bond dissociation energy of the weakest bond is 222–238 kJ mol⁻¹ and close to 2,4,6-trinitrotoluene (235 kJ mol⁻¹). The weakest bond of the other compounds may be the C NO₂ bond or the N N bond, and the strength of the N N bond is related to the nitro group on azole ring.     

N2O reduction over hexagonal BN nanosheet: effects of Stone–Wales defect and carbon pair doping

Nitrous oxide (N₂O) adsorption on the pristine and Stone–Wales (SW)-defected hexagonal BN nanosheets were investigated using density functional calculations including dispersion correction. It was found that N₂O is weakly adsorbed on the pristine sheet (h-BN) through van der Waals interaction with adsorption energy of ?1.2 kcal/mol. SW-defected sheet was found to be more reactive toward N₂O molecule having no significant change in electronic properties. However, the formation of B–B and N–N bond pairs in SW-defected sheet can be avoided, if there is a C–C pair doped in sheet (C₂-SW-h-BN). In this case, a strong adsorption is found due to large adsorption energy (?23.7 kcal/mol) and short bond length compared to the SW-h-BN complex. Interestingly, it was indicated that the N₂O molecule could be reduced into the N₂ on the C₂-SW-h-BN.     

Synthesis and structure of [Hg2(L)2(NO3)2] (L = (4-nitrophenyl)pyridin-2-ylmethyleneamine); a theoretical study on Hg–Hg bond in this and in linear Hg2X2 (X = F, Cl, Br, I, Ph) complexes

A new binuclear mercury(I) complex, [Hg₂(L)₂(NO₃)₂] (L = (4-nitrophenyl)pyridin-2-ylmethyleneamine), 1, has been synthesized and characterized by CHN analyses, IR, UV–vis spectroscopy and X-ray crystal structure analysis. The complex contains a metal–metal bonded core, [Hg–Hg]²⁺, in which a single bidentate imine ligand is coordinated to each mercury atom. The Hg atoms have an additional interaction with the oxygen atom of the NO₃ ^? ion. Theoretical studies show that the interaction energy between the two {Hg(L)NO₃} fragments is about 45–59 kcal/mol depending on the level of calculation. The Mayer-Mulliken and Wiberg bond indices (WBI) for Hg–Hg bond at different levels of theory are about 0.75–0.88 and 0.60–0.70, respectively, and are significantly larger than that for Hg–N and Hg–O bonds. The NBO calculations by using different methods and basis sets also show that the S character in Hg–Hg bond is very large (94.65–97.81 %). All above data for this complex are compared with those for linear Hg₂X₂ (X = F,Cl, Br, I, Ph) complexes. Interestingly, the bond order for Hg–Hg bond in complex 1 is comparable with that for Hg₂F₂ and larger than those in above linear complexes. This is consistent with the experimental data indicating that the Hg–Hg bond in 1 is shorter than that in all above complexes, except Hg₂F₂.     

Theoretical study on the radical–radical reaction mechanism of CH2I + NO2

The mechanisms of CH₂I with NO₂ reaction were investigated on the singlet and triplet potential energy surfaces (PESs) by the UB3LYP method. The energetic information is further refined at the UCCSD(T) and UQCISD(T) levels of theory. Our results indicated that the title reaction is more favorable on the singlet PES thermodynamically, and less competitive on the triplet one. On the singlet PES, the title reaction is most likely to be initiated by the carbon-to-oxygen approach forming the adduct IM1 (H₂ICONO-trans) without any transition state, which can isomerizes to IM2 (H₂ICNO₂) and IM3 (H₂ICONO-cis), respectively. The most feasible pathway is the 1, 3-I shift with C–I and O–N bonds cleavage along with the N–I bond formation of IM1 lead to the product P1 (CH₂O + INO), which can further dissociate to give P3 (CH₂O + I + NO). The competitive pathway is 1, 3-H shift associated with O–N bond rupture of IM1 to form P2 (CHIO + HNO). The theoretically obtained major product CH₂O and adducts IM1 and IM2 are in good agreement with the kinetic detection in experiment. The similarities and discrepancies between CH₂I + NO₂ and CH₂Br + NO₂ reactions are discussed in terms of the electronegativity of halogen atom and the barrier height of the rate-determining process. The present study may be helpful for further experimental investigation of the title reaction.     

First‐principles calculations of oxygen adsorption on the Ti3Al (0001) surface

Adsorption energies and density of states for O atoms adsorption on the Ti₃Al (0001) surface have been calculated using first‐principles calculations based on density functional theory. It is found that the order of O atom adsorption on the Ti₃Al (0001) surface is associated with the adsorption energy as well as the distance of O atoms because of the interaction. The adsorption energy mainly depends on the bond number and bond strength between O and Ti atoms, and the adsorption site with rich‐Ti surface (H_I and HCP_Al) is first priority. The adsorption energy decreases with the increase of the oxygen coverage because of the characteristics of the valence d‐orbitals of transition metals surface. Furthermore, the density of states indicates that the hybridization peak of O and Ti atoms is mainly from the contribution of Ti 3d‐ and O 2p‐orbitals, and the hybridization peak of O and Al atoms from the contribution of Al 2p‐ and O 2p‐orbitals. Copyright © 2016 John Wiley & Sons, Ltd.