We report on a study of influence of dopants (Ti and Ni) on the dehydrogenation properties of NaAlH4 using the ab initio density functional method. Calculations show that the influence of dopants on the electronic structure is much localized; only the electronic structures of atoms in the vicinity of the dopants were changed. The mechanisms by which Ti improves the dehydrogenation properties of NaAlH4 are sensitive to the occupation of Ti in NaAlH4. If Ti substitutes for an Al atom, it may form Ti−Al intermetallics, and if it occupies an interstitial site, it may “capture” H atoms to form TiH2 phase. In both cases, the [AlH4] groups were dramatically distorted, which is the main reason why Ti dopant improves the dehydrogenation properties of NaAlH4. The influence of Ni on the dehydrogenation properties of NaAlH4 is relatively in weak comparison to the Ti dopant, mainly because the Ni only affects the electronic distribution in its vicinity, and so no significant changes of the [AlH4] groups were observed in Ni doped systems.

•Negative formation energies of alloyed Cu6Sn5(0 1 0) surface were observed.•All alloying elements prefer to occupy the Cu site of Cu6Sn5(0 1 0) surface.•Alloyed systems show similar electronic structures except the Ce doped systems.Due to the reliability problem and high melting point, the development of lead-free solders is hindered. Alloying is considered to be a promising approach to design new Sn-based solders. Cu6Sn5 plays an important role in the quality of microelectronic packaging that formed at the interface of solder and Cu substrate. In the present study, first principles calculations were employed to study the occupation properties of alloying elements (A = P, Zn, Ag, In, Sb, Ce, Pb, and Bi) and anti-site defects (Cu and Sn) in (0 1 0) surface of Cu6Sn5 and their influence on the electronic structures of Cu6Sn5(0 1 0) surface. Formation energies were calculated to evaluate the occupation preferences of alloying elements in considered eight sites of Cu6Sn5(0 1 0) surface. Different alloying elements show different occupation preferences. The occupations of alloying elements in Cu6Sn5 surface show negative formation energies comparing the positive formation energies in bulk Sn. Therefore, the alloying elements will easily occur in the Cu6Sn5 compound during soldering process. Electronic structures were studied to reveal the occupation mechanisms of alloying elements, and the interactions between them and Cu6Sn5 surface. Large values of density of states appear around the Fermi energy level for Ce contained system. In terms of the lowest work function, the electrons in Ce contained systems will be much easier to lose than that in other contained systems. Therefore, alloying of Ce will greatly affect the stability and electrical properties of solder joints in microelectronic packaging.

•The stoichiometric (0 1 0) surface of O-phase of Ti2AlNb is the most stable surface.•Oxygen atoms prefer to adsorb at fcc-hollow and hcp-hollow sites.•The OTi and ONb bonds are stronger than the OAl bond in oxygen atom adsorbed Ti2AlNb surface.Adsorption behaviors of oxygen on the surfaces of O-phase Ti2AlNb were studied by first principles calculations to clarify the interaction mechanisms between oxygen and Ti2AlNb. The calculated surface energies of low index surfaces of Ti2AlNb indicate that the stoichiometric (0 1 0) surface is the most stable surface of Ti2AlNb. Various adsorption sites of oxygen atom on Ti2AlNb surfaces were considered to search the most stable adsorption configurations. The calculated adsorption energies and the electronic structures illustrate that O atoms tend to bond with Ti and Nb atoms. The hybriding between O p, Nb d and Ti d orbitals was observed, and the charges were found to transfer from nearest Ti and Nb atoms to the adsorbed oxygen, which produce the ONb and OTi bonds rather than the OAl bond. The weaker OAl bonding indicates that at the initial stage the oxidation of O-phase Ti2AlNb in high temperature could not form a protection alumina but instead of the Ti and Nb oxides.Download high-res image (102KB)Download full-size image

•Both carbon and graphene are N-doped with melamine formaldehyde resin.•Combined effect of N-doped graphene and CNTs as conductive matrices in Si-rGO/NCT.•The composite exhibits good rate and cycling performance.A Si-rGO/NCT composite, in which Si nanoparticles (SiNPs) are enwrapped with N-doped carbon and combine with N-doped graphene and CNTs as conductive matrices synthesized by simple solution-mixing and carbonization process with pyrolyzing melamine formaldehyde resin (MFR) is developed as a promising candidate anode material for lithium ion batteries (LIBs). The N-doped carbon outside SiNPs can not only improve the electrical conductivity of the composite, but also buffer the stress causing by huge volume change of SiNPs during the lithiation/delithiation process. The Si-rGO/NCT composite exhibits high specific capacity and good cycling stability (892.3 mAh g−1 at 100 mA g−1 up to 100 cycles), as well as improved rate capability. This approach provides a very facile route to obtain silicon-based anode materials.

The structural, optical and electrical properties of un-doped and (Al,Er) co-doped zinc oxide (ZnO) powders synthesized by hydrothermal method were investigated. The obtained samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive spectroscopy and magnetic measurements. XRD results reveal that the incorporation of Al and Er in ZnO matrix leads to the formation of a nanostructured hexagonal (würtzite) ZnO structure and α-Al2O3 secondary phase. High-resolution transmission electron microscopy image also shows the hexagonal shape of the ZnO nanoparticles. The magnetic behavior of the nanoparticles changes with concentration of dopant elements due to the competition between oxygen vacancies, secondary phase effect and exchange interaction between dopant elements.

Great progress has been made in developing highly efficient thermally activated delayed fluorescent (TADF) materials. However, developing highly efficient long-wavelength TADF emitters is still a challenge because a small energy gap (ΔEST) between the lowest singlet (S1) and triplet excited states (T1) and a relatively high fluorescence rate are difficult to achieve simultaneously in one molecule. Here, eleven donor–acceptor (D–A) type molecules using N3,N3,N6,N6-tetraphenyl-9H-carbazole-3,6-diamine (named DAC-II) as the electron donor and the 2-phenyl-quinoxaline-based electron acceptor are designed via introducing different electron-donating and electron-withdrawing groups into the acceptor and changing the connection position between the donor (D) and the acceptor (A). Quantum chemical calculations indicated that introducing the electron-donating groups (–OCH3, –CH3) into the phenyl ring of the acceptor, molecules 2 and 3, cannot change the emission property of molecule 1, thus molecules 2 and 3 could also be used as green TADF emitters like molecule 1. Introducing an electron-withdrawing unit (–CF3) into molecule 1, molecule 4, reduces the ΔEST value to 0.10 eV, while the radiative decay rate (kVE) is also reduced correspondingly. Changing the connection position between D and A, molecules 5 to 8, cannot reduce the ΔEST value and lowers the kVE value compared with molecules 1 to 4. However, introducing electron-withdrawing groups (–2F, –4F and –CN) into the quinoxaline moiety, molecules 9 to 11, contributes to both small ΔEST and large kVE for the emission process. The values of ΔEST of molecules 9 to 11 are in the range of 0.21 to 0.30 eV, and the maximum emission wavelengths of molecules 10 and 11 are 576 and 590 nm, respectively, which are promising to be used as efficient yellow and orange TADF emitters in organic light-emitting diodes.

The structural stability, electronic and optical properties of α-Si3N4 nanobelts orientating along the different directions with surface H, F and Cl modifications are investigated using first-principles methods. The stabilities of α-Si3N4 nanobelts are greatly affected by the surface modifications and increased in the order of H, Cl and F. All the modified α-Si3N4 nanobelts exhibit semiconductor characteristics. The effective masses of nanobelts are mainly affected by their orientations as well as surface modifications. The band gaps of α-Si3N4 nanobelts are found to be modulated by surface modifications. The Cl-modified nanobelts result in a smaller band gap than that of H- or F-modified ones. The electronic properties of α-Si3N4 nanobelts have significantly affected their optical properties. The linear light response ranges are mainly located in the ultraviolet region, where the absorption and refraction of light mainly occur, while the reflection is very weak. As the halogen coverage increases to 100%, the absorption edges of α-Si3N4 nanobelts have an obvious red-shift and new dielectric peaks appear. The Cl-modified nanobelts possess higher ε2(ω) peaks, lower absorption edges and better photoelectric characteristics than those of H- or F-modified nanobelts. The static optical parameters ε(0) and n(0) of 100% Cl-modified α-Si3N4 nanobelts are significantly larger than those of other nanobelts, indicating special applications in certain optical components.

The electronic structure and charge transport properties of thieno[2,3-b]benzothiophene (TBT) and its eight derivatives are investigated via density functional theory (DFT). The impact of different π-bridge spacers (1, the dimer of TBT; 2, vinyl; 3, phenyl; and 4, tetrafluorophenyl) and substituents (5, phenyl; 6, biphenyl; 7, naphthalenyl; and 8, benzothiophenyl) on the geometric structures, reorganization energy, absorption spectra, frontier orbitals, ionization potentials (IPs) and electron affinities (EAs) of all the compounds is explored to establish the relationship between the structure and properties. All the compounds show wide band gaps and low-lying HOMOs, and the IPs of all the TBT derivatives are higher than that of pentacene. The crystal packing interactions, transfer integrals and charge carrier mobilities of compounds 1, 2, 4 and 6 are also calculated. The calculated results demonstrated that these kinds of materials may exhibit good environmental stability and high charge mobility due to their large conjugated planar structure, close π-stacking arrangement, and multiple intermolecular interactions. For compounds 1 and 4, the predicted hole mobility is as high as 0.28 and 0.17 cm2 V−1 s−1, respectively, indicating that both of them benefit hole transport, while compounds 2 and 6 exhibit balanced charge transport properties with the hole and electron mobilities of 0.012 and 0.013 cm2 V−1 s−1, respectively, for compound 2. Compound 6 shows a relatively lower charge mobilities of 10−3 order of magnitude for both holes and electrons due to the larger reorganization energy and lower transfer integrals.

First principles calculations were carried out to study the interactions between carbon species and a β-spodumene matrix. Stabilities of low-index surfaces of β-spodumene with different terminations were firstly evaluated by surface energy calculations and results indicate that the Si–O–Li terminated (100) surface is the most stable surface with the lowest surface energy among the considered surfaces. The adsorption of carbon on the surface of β-spodumene and the formability of carbon-β-spodumene species are studied to clarify the interaction properties between them. The carbon species will be easily doped into or adsorbed on the surface of β-spodumene. The electronic structures reveal weak bonding interactions between the carbon layer and β-spodumene matrix, while these interactions can be strengthened by the adsorption of Li atoms on the carbon layer resulting in strong bonding interactions between them and therefore increasing the charge transfer between the carbon layer and β-spodumene matrix. Therefore the appearance of Li in the carbon species will improve the binding properties between the carbon species and β-spodumene matrix.

First principles calculations are carried out to study the hydrogen atom passivation properties of TiO2 nanotubes. The influence of charge on the stabilities of the TiO2 nanotubes with or without hydrogen atom passivation is studied. Two types of anatase TiO2 nanotube, denoted as (m, 0) and (0, n) (m = 6, 9 and n = 3, 6), were considered in the present work. The formation energy of the charged systems and the adsorption energy of the hydrogen atoms are evaluated. The negatively charged (6, 0) nanotubes and one charge state containing (0, 3) nanotubes possess low formation energies, indicating that they are easy to form among the considered nanotubes. The electronic structures of the TiO2 nanotubes are analyzed using several methods. It was found that the adsorbed hydrogen atoms can easily donate electrons to the oxygen atoms of the TNTs. Furthermore, the charge and hydrogen atom passivation cause the diverse distribution of states around the Fermi energy level, and therefore, may expand the potential applications of TiO2 nanotubes.

•The Ti, Mn, and Ni contained Y(BH4)3 are energetically unstable.•The K contained Y(BH4)3 may easily transform to the KY(BH4)4 compound.•The alkali metals can improve the dehydrogenation property of Y(BH4)3.First principles calculations are performed to study the influence of alloying elements Li, Na, K, Ti, Mn, and Ni and Y vacancy on the stability and dehydrogenation properties of Y(BH4)3. The formation energies of low and high temperature (LT and HT) phases of alloyed Y(BH4)3 are evaluated. Ti, Mn, and Ni elements and the Y vacancy containing Y(BH4)3 systems are endothermic. The Y vacancy is difficult to be generated due to the high energy demand. The alkali metals of Li, Na, and K prefer to occupy the interstitial sites in both the LT and HT phases of Y(BH4)3, especially the K element. The K containing systems show negative formation energy, even if eight K atoms are introduced. The K containing systems show similar structure characteristics with the KY(BH4)4 compound. Therefore, a phase transition from the K alloyed Y(BH4)3 to KY(BH4)4 is expectable. However, the transition from Li/Na alloyed Y(BH4)3 to corresponding Li/Na–Y(BH4)4 compounds is energetically unfavorable. Electronic structures of alloyed Y(BH4)3 are investigated to explore the reasons that why only K alloyed Y(BH4)3 can transform to KY(BH4)4 compound. In term of dehydrogenation properties, all alloyed systems show smaller dehydrogenation energies than the pure Y(BH4)3. The concentrations of alloying elements can greatly affect the dehydrogenation properties of alloyed Y(BH4)3.

•Surface stability of TiMn2 film and its hydrogen adsorption property are studied.•The interface between Mg and TiMn2 film is constructed.•Inserting of TiMn2 layers greatly promotes the hydrogenation properties of Mg.First principles calculations were carried out to study the stability and hydrogen adsorption properties of Mg/TiMn2 interface. The surface stability and hydrogen adsorption of TiMn2 were explored. The Mn terminated (001) is the most stable surface among the considered surfaces of TiMn2 and TiMn2 surface shows better hydrogen adsorption ability than the pure Mg surface. Two models coupling the Mg(0001) surface and the TiMn2(001) surface with different terminations were constructed to explore the Mg/TiMn2 interface. The Mg(0001)/Mn terminated TiMn2(001) with interface is much more stable than that of Ti terminated system. These two interfaces both show good hydrogen adsorption ability, in which the Mn terminated interface shows − 1.62 eV of hydrogen adsorption energy. The electronic structures of the considered systems are evaluated. The negative adsorption energies of hydrogen on the surface and interface systems are further explained by the analysis of the density of states.

•A stable AB stacking with a separation of 1.762 Å is obtained for Mg/Ni interface.•Tetrahedral site on the Ni side of the interface is the preferable site for hydrogen adsorbing.•Ni shows strong bonding interaction to capture hydrogen atoms in interfacial area.We have investigated the interaction of Mg/Ni interface and its hydrogen adsorption characteristics using first-principles calculations to obtain a better understanding of the Mg/Ni interface as a hydrogen storage material. The smallest work of adhesion of Mg/Ni interface is 4.28 J/m2 with AB stacking sequence in the studied systems. Hydrogen adsorption energy and electronic structures were evaluated to study the interaction characteristics between hydrogen and Mg/Ni interface. The hydrogen adsorption is energetically favored on all considered sites. The hydrogen atom prefers to adsorb on the tetrahedral site of the Ni side of the interface owning the lowest adsorption energy. The plane-averaged charge density and the density of states analysis indicate that the absorption of hydrogen could stabilize the Mg/Ni interface owing to the strongly bonding interactions between hydrogen atom and the host Mg and Ni atoms. Therefore, Mg/Ni interface provides a promising medium for hydrogen storage.

The hydrogenation and stability properties of the Mg/Ti interface are studied by first-principles calculations. The strain of lattice and movement of ions were imposed to search for a stable Mg/Ti interface. The anti-symmetrical configuration was found to be the most stable. The easiest transition pathway from anti-symmetrical to symmetrical configuration may be through the diagonal direction with no energy barrier. The hydrogen adsorption at distinguished positions in the Mg/Ti interface is investigated. The negative hydrogen adsorption energy reaches −0.991 eV at the top site in the interface, which will highly favor the thermodynamic stability of the Mg/Ti interface. The electronic structure is studied and it was found that the Ti acts as a hydrogen atom ‘capturer’ and strong interactions between H and its surrounding Ti and Mg atoms are expected. Thus, inserting Ti layers could create an interfacial zone where the adsorptions of hydrogen atoms may get stabilized and therefore improve the hydrogen storage properties of Mg.

•A transport media of Al–H complex was observed in Ti doped Na3AlH6.•Dopant Ti stretches Al–H bond and promotes the hydrogen dissociation from Na3AlH6.•A mechanism that Ti improves dehydrogenation properties of Na3AlH6 was proposed.In the present work, ab initio calculations were performed for the Ti-doped Na3AlH6 to investigate influence of dopant Ti on the hydrogenation/dehydrogenation properties of Na3AlH6. Substitution of Ti for Al and Na atoms, respectively, and an interstitial occupation of Ti in this compound were studied. It was found that Ti prefers to substitute for Al atom with the lowest occupation energy of 0.64 eV among the considered systems. The influence of Ti on hydrogenation/dehydrogenation properties of Na3AlH6 was sensitive to its occupation behavior. Ti greatly decreases the dehydrogenation energy of Na3AlH6 if it substituted for a Na atom. A mechanism described the Ti catalytic reversible reaction of NaAlH4 → Na3AlH6 was proposed based on the electronic analysis in this paper.

Syntheses, structural, optical and magnetic characterizations of codoped ZnO nanoparticles have been reported. Nanoparticles of Zn1−2xCexMnxO (x=0.00, 0.01, 0.02, 0.03, 0.04, and 0.05) were synthesized using a microwave-assisted combustion method. Structural, optical and magnetic properties were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), diffuse reflectance spectroscopy (DRS), photoluminescence spectroscopy (PL) and a vibrating sample magnetometer (VSM). The observed shift in XRD peak position, change in peak intensity, cell parameters, volume and stress confirmed the substitution of cerium-manganese (Ce–Mn) dopants within ZnO lattice. The synthesized nanoparticles show different microstructure without changing the parent hexagonal wurtzite structure of zinc oxide (ZnO). The average crystallites size was decreased from 43 to 21 nm. Energy dispersive X-ray spectra confirmed the presence of Ce and Mn in ZnO system and the weight percentage was nearly equal to their nominal stoichiometry. DRS analysis showed a decrease in the energy gap with increasing dopants content. The observed luminescence in the green, violet and blue regions strongly depends on the nature of the doping elements and their concentration owing to the formation of different oxygen vacancy, zinc interstitial, and surface morphology. Our results demonstrate that Mn ions doping concentration play an important role in the observed room temperature ferromagnetism (RTFM) of Ce–Mn codoped ZnO nanoparticles. First- principles calculation results indicate that Ce governs the stability, while Mn adjusts the magnetic characteristics in codoped ZnO.

•Ce, Co co doped ZnO nanoparticles are produced using a microwave combustion route.•As synthesized nanoparticles have the wurtzite structure.•Morphological investigation revealed the nanoparticles in the range of 25–60 nm.•DRS measurements showed decrease in the energy gap with increasing dopants content.•DFT indicates Ce governs stability, while Co adjusts the magnetic characteristics.A simple one-step microwave-assisted combustion method using urea as a fuel, was applied to develop the nanophase powders of ((Zn1−2xCexCox) O (x = 0.00, 0.01, 0.02, 0.03, 0.04, and 0.05)). The results emphasize that by changing the codopant concentration it is feasible to fine-tune structural, morphological, optical and magnetic properties. The synthesized nanoparticles gave rise to new microstructures without changing the basic hexagonal wurtzite structure. The substitution of Ce and Co into ZnO lattice was confirmed from the shift in XRD peaks position, changes in peaks intensity, and cell parameters. Energy dispersive X-ray spectra confirmed the presence of Ce and Co within ZnO system; the weight percentage was close to their nominal stoichiometry. Ultraviolet–visible (UV–Vis) spectroscopy analysis indicated that the optical band gap decreased with the increase of Ce and Co codoping concentration. It is clear from SEM images that the average particles size decreased from 50 nm to 25 nm when codoping concentration was increased up to 0.05 M. Photoluminescence spectra exhibited the emission bands in ultra-violet and blue–green regions. Magnetization-Field (M–H) hysteresis loops revealed that the codoped nanopowders exhibited room temperature ferromagnetism (RTFM). Using first principles calculations, based on density functional theory, electronic and magnetic properties of codoped ZnO for different dopants concentration, were predicted. It is found that the observed RTFM is originated mainly from spin polarization of Co-d orbital, Ce-f orbital has partial contribution.Microwave-assisted combustion method was used to develop the nanophase powders. The shift in the XRD peak position, changes in peak intensity, cell parameters, and cell volume confirms the substitution of Ce and Co into ZnO lattice. SEM images show that the average crystal size decreased from 50 nm to 25 nm when co doping concentration was increased. The vibrating sample magnetometer (VSM) revealed that the doped samples exhibited ferromagnetism at room temperature. Using first principles calculations, we predicted the magnetic and electronic properties of co-doped ZnO for different dopants concentration.

•The O-terminate Al2O3(0001) and TiAl(111) interface owns the lowest work of adhesion.•The O–Al bond in TiAl side is stronger than the O–Ti bond.•The O–Al interaction dominates the adhesion between TiAl(111) and Al2O3(0001) surfaces.First principles calculations were carried out for α-Al2O3(0001) surface and γ-TiAl(111)/α-Al2O3(0001) interface to study the adhesion properties of the interface and to clarify the mechanisms that govern the adhesion of TiAl and its oxidation product Al2O3. Two type interface models, the TiAl(111) with Al- and O-terminated α-Al2O3(0001) surfaces denoted as T(A1)-type and T(OT)-type interface, respectively, were considered. The Universal Binding Energy Relation (UBER) was used to determine the separation between TiAl and Al2O3 and the work of adhesion of the γ-TiAl(111)/α-Al2O3(0001) interface. Optimization was then performed for all interfaces considered here using the separation obtained with UBER. The lowest work of adhesion is −1.05 J/m2 for the T(A1)-type interface and is −4.04 J/m2 for the T(OT)-type interface. There exists competition between O–Ti and O–Al (on the TiAl side) interactions; however O–Al bond is stronger than O–Ti bond because the main body of the Al valences is involved in the hybriding with O p electrons, while only part of the Ti d valence is involved in the O–Ti bonding. Thus the O–Al interaction dominates the adhesion between TiAl(111) and Al2O3(0001) surfaces, and it can be inferred that an Al-rich TiAl surface will favor the adhesion between TiAl/Al2O3.

A basic understanding of the affinity between the hydroxyapatite (HA) and α-Ti surfaces is obtained through electronic structure calculations by first-principles method. The surface energies of HA(0001), HA (011̅0), HA (101̅1), and Ti(0001) surfaces have been calculated. The HA(0001) presents the most thermodynamically stable of HA. The HA/Ti interfaces were constructed by two kinds of interface models, the single interface (denoted as SI) and the double-interface (denoted as DI). Two methods, the full relaxation and the UBER, were applied to determine the interfacial separation and the atomic arrangement in the interfacial zone. The works of adhesion of interfaces with various stoichiometric HA surfaces were evaluated. For the HA(0001)/Ti(0001) interfaces, the work of adhesion is strongly dependent on the chemical environment of the HA surface. The values are −2.33, −1.52, and −0.80 J/m2 for the none-, single-, and double-Ca terminated HA/Ti interfaces, respectively. The influence of atomic relaxation on the work of adhesion and interface separation is discussed. Full relaxation results include −1.99 J/m2 work of adhesion and 0.220 nm separation between HA and Ti for the DI of 1-Ca-HA/Ti interface, while they are −1.14 J/m2 and 0.235 nm by partial relaxation. Analysis of electronic structure reveals that charge transfer between HA and Ti slabs occurs during the formation of the HA/Ti interface. The transfer generates the Ti–O or Ti–Ca bonds across the interface and drives the HA/Ti interface system to metallic characteristic. The energetically favorable interfaces are formed when the outmost layer of HA comprises more O atoms at the interface.Keywords: first-principles; HA/Ti interface; hydroxyapatite; work of adhesion

The energetic stability and electronic properties of unpassivated, hydrogen (–H) and hydroxyl (–OH) passivated α-Si3N4 nanobelts orientating along the [101], [210], [011], [100], [001], and [110] directions are investigated by first-principles calculations. Calculations show that the energetic stabilities of α-Si3N4 nanobelts depend weakly upon orientations of nanobelts, but sensitively on passivation treatments. The most stable nanobelt is the OH cluster partially passivated α-Si3N4, followed by the H atom fully passivated and the unpassivated systems. All the unpassivated nanobelts show metallic characteristics due to the presence of dangling bonds of surficial atoms in nanobelts, while all the passivated nanobelts exhibit semiconducting characteristics. The valence band maximum (VBM) and the conduction band minimum (CBM) mainly originate from the surface N-2p and Si-3p states, respectively. For α-Si3N4 nanobelts orientating along [101], [210], [011] and [110] directions, the OH passivated systems exhibit a much smaller band gap than the H passivated systems, while the [100] and [001] orientated nanobelts exhibit the opposite band-gap properties.

•Most alloying elements stabilize Mg17Al12 with negative occupation energy.•The alloying element and oxygen co-existed Mg17Al12 are stable.•Strong bonding interactions existed between alloying element and host atoms.Influence of alloying elements (Ca, Mn, Ni, Cu, Zn, Zr, Sn, and La) and oxygen on stability and elastic properties of Mg17Al12 has been studied by first principles total energy calculations. The occupation preferences of oxygen and alloying elements in Mg17Al12 are identified. Ca, Zr, and La tend to substitute for Mg atoms, Zn, Cu, and Ni prefer to occupy Al site, and Mn and Sn show positive occupation energy for substituting both Mg and Al atoms. The impurity oxygen prefers to occupy interstitial sites surrounded by four Mg atoms regardless the presence of alloying elements in this system. Elastic constants were estimated to evaluate the mechanical stability of alloyed systems. The results show that alloys which own negative occupation energy also satisfy the mechanical stability criteria. Electronic structures were analyzed to clarify the intrinsic mechanisms of how alloying elements and oxygen influence the stability of Mg17Al12. The stabilization effect of alloying elements and oxygen was found to originate from the strong bonding interaction with the matrix.

•Bonding of TiAl/TiO2 interface is associated with O transferring from TiO2 to TiAl.•Ti vacancy increases bonding interaction between O and Al atoms at TiAl/TiO2 interface.•Oxygen atoms are shielded by Al atomic layer in Nb-containing TiAl/TiO2 interface.Influence of defects (Ti vacancy and Nb dopant) on the bonding of TiAl/TiO2 interface was studied via first-principles calculations. It was shown that the bonding strength and the stability of TiAl/TiO2 interface were weakened by the presence of Ti vacancy and dopant Nb. The defects could also change the relative stability of the interface with different couplings between the two compounds. Electronic structure of the interface was analyzed and the influence mechanisms of defects on the bonding of interface were presented.

•All doped systems are energetically unstable comparing to the undoped COF-108.•Li and Na can move conduction band crosses the Fermi energy level.•Weakly bonded electrons in Li/Na doped COF-108 are produced near the Fermi energy.•Enhancement of H2 uptake may due to polarization of H2 by weakly bonded electrons.Mechanisms of dopants (Li, Na, Mg, and Al) influence on hydrogen uptake in COF-108 were investigated by means of first principles. The binding energy of dopants in COF-108 was estimated from the first principles total energy calculations. All doped systems are shown positive binding energies with the metallic state of the dopant as the reference. The lowest binding energy of 0.518 eV appeared in the Na-doped system while a large amount of energy (2.692 eV) is required for Al to dope into COF-108. Electronic structure analysis shows that dopants Li and Na move the conduction band crossing the Fermi energy level and introduce weakly bonded electrons near the Fermi energy, which may polarize the hydrogen molecules. It is expectable that interaction between hydrogen molecule and the host COF-108 could be enhanced by the polarization of hydrogen molecule. Therefore the hydrogen uptake will be improved in the doped systems. Dopant Mg slightly reduces the band gap between the valence and conduction bands, but is hard to build chemical bonds with the host atoms owing to the less overlaps between the bond peaks of Mg and the COF-108. It hardly affects the electron distributions of the COF-108 and therefore weakly changes the chemical interactions between atoms in COF-108.

•All dopants prefer to substitute for the Mg atom.•The B substitution has significant influence on H dissociation.•Dehydrogenation was improved by dopants mainly by distorting the BH4 units.First principles calculations on Fe, Ni, and Nb doped Mg(BH4)2 were carried out to study the influence of dopants on dehydrogenation properties of Mg(BH4)2. It was shown that all dopants considered prefer to substitute for Mg with relatively smaller occupation energies comparing to the B substitution and the interstitial occupation. However, the B substitution shows smaller hydrogen dissociation energy than the Mg substitution. Mechanisms that dopants used to improve dehydrogenation properties of Mg(BH4)2 are different. For Mg substitution, Fe strongly interacts with one H atoms of the [BH4] group, distorts its structural stability and therefore lowers the hydrogen dissociation energy, Ni may attract one particular H atom of the [BH4] group and weakens the interactions between the B and other H atoms reducing the hydrogen dissociation energy, and the Nb however may drive the formation of NbB2 and improves the dehydrogenation properties as well. In the B substitution, Fe interacts with the one of H atoms and decreases its structure stability, the Ni will attract its neighbor atoms to form a regular group which is almost identical in structure to that of the NiH4 group in Mg2NiH4, and the NbH2 and MgH2 are likely to be generated by Nb doping.

The interaction between new two-dimensional carbon allotropes, i.e., graphyne (GP) and graphdiyne (GD), and light metal complex hydrides LiAlH4, LiBH4, and NaAlH4 was studied using density functional theory (DFT) incorporating long-range van der Waals dispersion correction. The interaction of light metal complex hydrides with GP and GD is much stronger than that with fullerene because of the well-defined pore structure of GP and GD. Such strong interactions greatly affect the degree of charge donation from the alkali metal atom to AlH4 or BH4, consequently destabilizing the Al–H or B–H bonds. Compared to the isolated light metal complex hydride, the presence of GP or GD can lead to a significant reduction of the hydrogen removal energy. Most interestingly, the hydrogen removal energies for LiBHx on GP and with GD are found to be lowered at all the stages (x from 4 to 1), whereas the H-removal energy in the third stage is increased for LiBH4 on fullerene. In addition, the presence of uniformly distributed pores on GP and GD is expected to facilitate the dehydrogenation of light metal complex hydrides. The present results highlight new interesting materials to catalyze light metal complex hydrides for potential application as media for hydrogen storage. Because GD has been successfully synthesized in a recent experiment, we hope the present work will stimulate further experimental investigations in this direction.

Interaction between atoms in Mg/TiAl sandwiched films and hydrogenation of the films are studied by first-principles calculations. The formation energy is used to estimate the energetic stability of the Mg/TiAl films. The Mg/TiAl sandwiched films are more stable than the pure Mg film. The adsorptions of hydrogen in the Mg/TiAl films are investigated. Inserting TiAl layers can improve the hydrogenation properties of Mg film. The lowest hydrogen adsorption energy of −1.163 eV appears in hydrogen adsorbed Mg(0001)/TiAl(110) film, and the second lowest adsorption energy is −0.333 eV for hydrogen adsorbed Mg(0001)/TiAl(111) film, while the adsorption energy reaches a positive value of 0.089 eV for hydrogen adsorbing in Mg(0001) film. The electronic structure analysis illustrates that strong interactions between H and its surrounding Ti and Mg atoms are expectable. Thus, in the Mg/TiAl films Ti and Mg act as active sites to capture hydrogen atoms and, therefore, hydrogenation properties of Mg/TiAl films are improved compared to the pure Mg film.

We studied the adsorption behavior of oxygen on low index surfaces of γ-TiAl via first principles to investigate the mechanism that drives the adsorption behavior. The (100) surface is the most stable surface energetically followed by the (111), (110) and (001) surfaces. A study of the adsorption of a single oxygen atom on surfaces of TiAl showed that the O atom prefers the Ti-rich environment that has a high potential of generating TiO2. Competition between O-Al bonding and O-Ti bonding was observed in the O adsorbed surface regions. However, the O-Ti interaction dominates the adsorption behavior in all considered systems except when O is adsorbed on an Al-terminated (001) surface as the O–Al bond is stronger than O–Ti bond. A linear relationship between adsorption energy and integration of orbital overlaps between the O atom and the metals is obtained, which indicates that the electronic structure controls the adsorption behavior of an O atom on a γ-TiAl surface — an opportunity to improve the oxidation resistance of γ-TiAl based alloys.Highlights► Surface stability of gamma-TiAl is in the order of (100), (111), (110), and (001). ► O could either adsorb or absorb in (100) surface with similar adsorption energies. ► The fcc-Al and hcp-Al sites are favorable sites if O adsorbs on (111) surface. ► O–Ti bond is stronger than O–Al bond, but a competition between them was observed. ► Oxidation resistance of gamma-TiAl could be improved by enhancing O–Al bonding.

We studied the influence of Ti and Al dopants on the dehydrogenation properties of Mg(BH4)2 via first principles calculations. The dopants only affect the electronic structure of matrix in their vicinity as they use various mechanisms to improve the dehydrogenation properties of Mg(BH4)2. Ti prefers to occupy the Mg site, whereas Al usually substitutes for the B atom and tends to form AlH4. However, one of the Al–H bonds is weak and will be broken during dehydrogenation. In Ti-doped systems, dehydrogenation properties of Mg(BH4)2 change depending on which site the Ti atom occupies. If it substitutes for Mg, the interaction between the Ti and the B atoms is weaker than the Mg–B interaction in the undoped Mg(BH4)2. When Ti substitutes for a B atom, it can only hold two H atoms and so is likely to generate a metal hydride such as TiH2. The other two H atoms are held by weak bonds and so easily may be released during dehydrogenation. This means that Ti is a good candidate to improve the dehydrogenation properties of Mg(BH4)2.

A first principle study was carried out to investigate the dehydrogenation properties of metal (001) surface doped MgH2. Site preference of dopants was identified and dehydrogenation properties of the doped systems were analyzed based on the total energy and electronic structure calculations. It was shown that Al and Ti prefer to substitute for Mg atoms, whereas Mn and Ni prefer to occupy interstitial sites. The mechanisms that dopants improve the dehydrogenation properties of the considered systems were clarified. Al weakens the interactions between the Mg and the H atoms and has high potential to drive a formation of an Al–Mg cluster, and therefore improves the dehydrogenation performance of the Al doped system. Ti strongly interacts with its neighboring H atoms, distorts their positions, and could potentially generate a TiH2 phase by attracting two H atoms. Mn greatly distorts the surface structure and causes a dramatic reduction on the dehydrogenation energy in the Mn interstitially doped system. A Ni–H tetrahedral cluster is observed, which acts as a seed to form Mg2NiH4 phase, in the Ni doped MgH2 (001) surface. Therefore, the improvement of the dehydrogenation properties of Ni doped system is expectable due to the formation of thermodynamically less stable Mg2NiH4 phase.Highlights► Occupation energies of dopants in MgH2 (001) surface are lower than 1.5 eV. 2. ► Al and Ti substitute for Mg atoms, whereas Mn and Ni occupy interstitial sites. ► There is high potential to form a second phase in the doped systems. ► Desorption property is improved by surface distortion & formation of second phase.

First principle calculations have been performed to explore the adsorption characteristics of water molecule on (001) and (110) surfaces of magnesium hydride. The stable adsorption configurations of water molecule on the surfaces of MgH2 were identified by comparing the total energies of different adsorption states. The (110) surface shows a higher reactivity with H2O molecule owing to the larger adsorption energy than the (001) surface, and the adsorption mechanisms of water molecule on the two surfaces were clarified from electronic structures. For both (001) and (110) surface adsorptions, the O p orbitals overlapped with the Mg s and p orbitals leading to interactions between O and Mg atoms and weakening the O–H bonds in water molecule. Due to the difference of the bonding strength between O and Mg atoms in the (001) and (110) surfaces, the adsorption energies and configurations of water molecule on the two surfaces are significantly different.Research highlights► H2O prefers to adsorb on (110) surface with an adsorption energy of − 0.96 eV. ► Surface structure was distorted by the adsorption of H2O. ► Bonding interactions between O and Mg atoms affect adsorption of water molecule. ► It could potentially generate Mg(OH)2 if H2O dissociates on surfaces of MgH2.

We report a study of the influence of Ti and Ni dopants on the stability and bonding interactions of LiAlH4 using the first-principles method. Both the Ti and the Ni prefer to occupy an interstitial site in the LiAlH4 owing to lower occupation energies estimated from the total energy calculations. Calculations show that the bonding interactions between the Al and the H atoms within the [AlH4] groups were significantly reduced by the dopants, and both the stability and the geometry of the [AlH4] group were distorted in the doped LiAlH4 systems. However, Ti and Ni use different mechanisms to improve the dehydrogenation properties of LiAlH4. The Ti dopant tends to interact with the Al atom in its neighbouring [AlH4] to ‘free’ the H atoms from these [AlH4] groups. The effect of Ni dopant on the stability and the bonding interactions of the LiAlH4 is due to the induction of the Ni d electrons that could cause a bonding interaction between the Ni and the Al atoms, strengthening the interactions between the Li and the H atoms, and ‘freeing’ the H atoms from the neighbouring [AlH4] groups as well.

First principles calculations on an Al, Ti, Mn, and Ni doped MgH2 (110) surface were carried out to study the influence of dopants on the dehydrogenation properties of MgH2. It was shown that Al prefers to substitute for an Mg atom, whereas Ti, Mn, and Ni prefer to occupy interstitial sites. The dopants used different mechanisms to improve the dehydrogenation properties of MgH2. Al weakens the interactions between the Mg and the H atoms in its vicinity and so slightly improved the dehydrogenation properties of the Al doped system. The H atoms near the dopants of the transition metal doped systems were dramatically distorted. Ti has a high potential to generate a TiH2 phase by attracting two H atoms, which frees one H atom from its host Mg atom. The dehydrogenation properties of the Mn doped system were improved by the formation of a Mn−H cluster with a similar structure to Mg3MnH7 but weaker interactions between its atoms. If the MgH2 (110) surface is doped with Ni, the Ni will attract four H atoms to form a regular tetrahedral NiH4 group almost identical in structure to that in Mg2NiH4. The improvement of the dehydrogenation properties of Ni-doped MgH2 is expected as the bonding between the Mg and the H atoms is weakened, and there is a high possibility that the Mg2NiH4 phase will be formed, which is thermodynamically less stable than the MgH2 in this system.

Electronic structure and the total energy of the Mg(NH2)2 were calculated using first principle theory. The bonding characteristics and decomposition mechanism of the Mg(NH2)2 were clarified based on the electronic structure and the total energies. The bonding interactions of the Mg atoms with the two [NH2] ligands are slightly different, while it shows a significant difference in the bonding interactions between the N and the H atoms within the [NH2] ligands. The weakest bond is the N2–H2 bond in the [NH2](2) ligand. A decomposition mechanism of the Mg(NH2)2 was proposed based on the bonding characteristics. The decomposition of the Mg(NH2)2 is performed by two steps. First H+ cations decompose from the [NH2] ligands due to their weaker bonds with the matrix, and then [NH2]− anions decompose. The H+ cations and [NH2]− anions therefore react each other to generate NH3. For the Mg(NH2)2 + LiH systems, it is most likely that the Mg(NH2) decomposes to MgNH, H+cation, and [NH2]− anion first, and then the released H+ cation and [NH2]− anion either react each other to form NH3 and then reacts with LiH, or directly react with Li+ cation and H− anion if LiH is decomposed. Both of the reactions generate the LiNH2 and the H2. And the LiNH2 further mixes with MgNH to form the LiMgN2H3. The is the first step of a multi-step dehydrogenation process of the Mg(NH2)2–LiH system [Isobe S, Ichikawa T, Leng H, Fujii H, Kojima Y. Hydrogen desorption processes in Li–Mg–N–H systems. J Phys Chem Solids 2008;69:22234.].

The stability and bonding mechanism of ternary magnesium based hydrides (Mg, X, Y)H2, X or Y = Fe or Ni, were studied by means of electronic structure and total energy calculations using the FP-LAPW method within the GGA. The influence of the selected alloying elements on the stability of the hydride was determined from the difference between the total energy of the alloyed systems and those of the pure metal and the hydride. Full relaxation was carried out against the overall geometry of the supercell and the internal coordinates of the H atoms. The bonding interactions between the alloying atoms and their surrounding H atoms were estimated using the variation of the total energy against the coordinates of H atoms. The alloying elements, Fe and Ni, destabilised MgH2. This combined with the weak bonds between the alloying elements and H atoms improved the dehydrogenation properties of MgH2.

•Oxygen atoms are the adhesion media connecting TiAl and TiO2 slabs in the TiAl/TiO2 interface.•Alloying elements improve the adhesion ability TiO2 and TiAl and enhance the stability of TiAl/TiO2 interface.•Alloying elements distort electronic structures of TiO2 slab and affect adhesion ability between TiAl and its oxide scale.First-principles calculations were performed to study the adhesion of the M alloyed TiAl and TiO2 interface (M = Si, Cr, Co, Ni, Y, Zr, Nb, Mo, Pd, and W). The occupation of alloying elements in the TiAl/TiO2 interface was examined and the influence of alloying elements on the adhesion of the interface was then clarified. The alloying elements stabilize both the TiAl surface and TiAl/TiO2 interface but with different degrees.The Y, Nb and Pd greatly improve the adhesion of TiO2 on TiAl matrix, while others illustrate relatively weak effect. The geometric configuration and electronic structures of elements in the interface zone were studied to investigate the bonding interactions between the alloyed TiAl and TiO2 layers. The oxygen atoms are found to be the adhesion media connecting the alloyed TiAl and TiO2 slabs in the TiAl/TiO2 interface and may affect the spallation of oxide scale from TiAl matrix.

We report a study of the influence of Ti and Ni dopants on the stability and bonding interactions of LiAlH4 using the first-principles method. Both the Ti and the Ni prefer to occupy an interstitial site in the LiAlH4 owing to lower occupation energies estimated from the total energy calculations. Calculations show that the bonding interactions between the Al and the H atoms within the [AlH4] groups were significantly reduced by the dopants, and both the stability and the geometry of the [AlH4] group were distorted in the doped LiAlH4 systems. However, Ti and Ni use different mechanisms to improve the dehydrogenation properties of LiAlH4. The Ti dopant tends to interact with the Al atom in its neighbouring [AlH4] to ‘free’ the H atoms from these [AlH4] groups. The effect of Ni dopant on the stability and the bonding interactions of the LiAlH4 is due to the induction of the Ni d electrons that could cause a bonding interaction between the Ni and the Al atoms, strengthening the interactions between the Li and the H atoms, and ‘freeing’ the H atoms from the neighbouring [AlH4] groups as well.

The hydrogenation and stability properties of the Mg/Ti interface are studied by first-principles calculations. The strain of lattice and movement of ions were imposed to search for a stable Mg/Ti interface. The anti-symmetrical configuration was found to be the most stable. The easiest transition pathway from anti-symmetrical to symmetrical configuration may be through the diagonal direction with no energy barrier. The hydrogen adsorption at distinguished positions in the Mg/Ti interface is investigated. The negative hydrogen adsorption energy reaches −0.991 eV at the top site in the interface, which will highly favor the thermodynamic stability of the Mg/Ti interface. The electronic structure is studied and it was found that the Ti acts as a hydrogen atom ‘capturer’ and strong interactions between H and its surrounding Ti and Mg atoms are expected. Thus, inserting Ti layers could create an interfacial zone where the adsorptions of hydrogen atoms may get stabilized and therefore improve the hydrogen storage properties of Mg.

The structural stability, electronic and optical properties of α-Si3N4 nanobelts orientating along the different directions with surface H, F and Cl modifications are investigated using first-principles methods. The stabilities of α-Si3N4 nanobelts are greatly affected by the surface modifications and increased in the order of H, Cl and F. All the modified α-Si3N4 nanobelts exhibit semiconductor characteristics. The effective masses of nanobelts are mainly affected by their orientations as well as surface modifications. The band gaps of α-Si3N4 nanobelts are found to be modulated by surface modifications. The Cl-modified nanobelts result in a smaller band gap than that of H- or F-modified ones. The electronic properties of α-Si3N4 nanobelts have significantly affected their optical properties. The linear light response ranges are mainly located in the ultraviolet region, where the absorption and refraction of light mainly occur, while the reflection is very weak. As the halogen coverage increases to 100%, the absorption edges of α-Si3N4 nanobelts have an obvious red-shift and new dielectric peaks appear. The Cl-modified nanobelts possess higher ε2(ω) peaks, lower absorption edges and better photoelectric characteristics than those of H- or F-modified nanobelts. The static optical parameters ε(0) and n(0) of 100% Cl-modified α-Si3N4 nanobelts are significantly larger than those of other nanobelts, indicating special applications in certain optical components.

The electronic structure and charge transport properties of thieno[2,3-b]benzothiophene (TBT) and its eight derivatives are investigated via density functional theory (DFT). The impact of different π-bridge spacers (1, the dimer of TBT; 2, vinyl; 3, phenyl; and 4, tetrafluorophenyl) and substituents (5, phenyl; 6, biphenyl; 7, naphthalenyl; and 8, benzothiophenyl) on the geometric structures, reorganization energy, absorption spectra, frontier orbitals, ionization potentials (IPs) and electron affinities (EAs) of all the compounds is explored to establish the relationship between the structure and properties. All the compounds show wide band gaps and low-lying HOMOs, and the IPs of all the TBT derivatives are higher than that of pentacene. The crystal packing interactions, transfer integrals and charge carrier mobilities of compounds 1, 2, 4 and 6 are also calculated. The calculated results demonstrated that these kinds of materials may exhibit good environmental stability and high charge mobility due to their large conjugated planar structure, close π-stacking arrangement, and multiple intermolecular interactions. For compounds 1 and 4, the predicted hole mobility is as high as 0.28 and 0.17 cm2 V−1 s−1, respectively, indicating that both of them benefit hole transport, while compounds 2 and 6 exhibit balanced charge transport properties with the hole and electron mobilities of 0.012 and 0.013 cm2 V−1 s−1, respectively, for compound 2. Compound 6 shows a relatively lower charge mobilities of 10−3 order of magnitude for both holes and electrons due to the larger reorganization energy and lower transfer integrals.