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The structural, electronic, and magnetic properties of the stoichiometric (001) surface of double perovskite Sr2FeMoO6 have been studied by using a 10-layer FeMoO4 and SrO terminated (001)-oriented slab model and the first-principles projector augmented wave potential within the generalized gradient approximation as well as taking into account the on-site Coulomb repulsive (U = 2.0 eV for Fe and 1.0 eV for Mo). An outwards relaxation is observed for several layers near surface, and the accompanying layer rumpling has a decrease tend from surface layer to inner layer. Along Fe-O-Mo-O-Fe or Mo-O-Fe-O-Mo chains, the oxygen atom is closer to the adjacent Mo atom than to the adjacent Fe atom. In FeO6 or MoO6 octahedra, the two axial TM−O bonds are not equal, and especially, the surface dangling bond makes the remaining one axial TM−O bond slightly shorter than four equally equatorial TM−O bonds. The half-metallic nature and a complete (100%) spin polarization character ensure the FeMoO4 and SrO terminated (001)-oriented slab of double perovskite Sr2FeMoO6 a potential application in spintronics devices. The Fe+3 and Mo+5 ions are still in the (3 d5, S = 5/2) and (4 d1, S = 1/2) states with positive and negative magnetic moments respectively and thus antiferromagnetic coupling via oxygen between them. There is no direct interaction between two nearest Fe-Fe or Mo-Mo pairs, whereas the hybridizations between Fe 3 d and 4 s, O 2 s and 2 p, as well as Mo 4 d, 5 s and 5 p orbitals are fairly significant. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The geometrical, electronic and magnetic properties of the ZnMoM (M=S, Se and Te) have been studied by spin-polarized first-principles calculation. The optimized lattice constants of 5.535, 5.836 and 6.274 Å for M=S, Se and Te are related to the atomic radius of 1.09, 1.22 and 1.42 Å for S, Se and Te atoms, respectively. The ZnMoM are magnetic half-metallic (HM) with the spin-down conventional band gaps of 2.899, 2.126 and 1.840 eV, while the HM band gaps of 0.393, 0.016 and 0.294 eV for M=S, Se and Te, respectively. At the Fermi level, the less than half-filled Mo- orbital hybridizated with the less M- orbital contributes only spin-up channel leading ZnMoM an HM ferromagnetism. The tetrahedral crystal field formed by adjacent three Zn atoms and one M atom splits the spin-up channel (majority spin) of Mo- orbital into three-fold degenerate states at the Fermi level and double degenerate states below the Fermi level. The exchange splitting energies of the ZnMoM are −2.611, −2.231 and −1.717 eV for M=S, Se and Te, respectively. The results provide an useful theoretical guidance for ZnMoM applications in spintronic devices. [ABSTRACT FROM AUTHOR]

Abstract: The effects of a single C-chain on the structural and electronic properties of the H terminated zigzag AlN nanoribbons (ZAlNNRs) have been investigated systemically by using the first-principles. The results show that in perfect 7-ZAlNNR for example, the states of the lowest unoccupied conduction band (LUCB) and the highest occupied valence band (HOVB) at zone boundary Z are edge states their charges are localized at edge Al and N atoms, respectively. Introducing a single C-chain and changing its position lead to the LUCB and HOVB getting closer with each other. Similar to the edge states existing in perfect ZAlNNR, the flat dispersion border states also exist in a single C-chain decorated ZAlNNR, but their charges are localized at border C–N and C–Al for LUCB and HOVB, respectively. Furthermore, for Nz -ZAlNNR-C(n) with ribbon width Nz =2, 3, 4, 5, 6, 7 and 10, only Nz -ZAlNNR-C(1) has a direct band gap, while the other Nz -ZAlNNR-C(n) has an indirect band gap. Variation of the band gap with C-chain position n shows that, for Nz -ZAlNNR-C(n) of arbitrary width Nz , the Nz -ZAlNNR-C(1) and Nz -ZAlNNR-C(2) have nearly identical the minimum band gap of 0.132eV and nearly identical the maximum band gap of 1eV, respectively, except the maximum band gap of 0.63eV for 2-ZAlNNR-C(2) because it belongs to the group of C-chain substituting the right edge Al–N chain, the band gap of this group decreases linearly with increasing ribbon width Nz . For 3-, 4-, 5-, 6-, 7- and 10-ZAlNNR-C(n), the band gap decreases successively for C-chain position n from 2 to 3, 4, 5, 6, 7 and 10, respectively. [ABSTRACT FROM AUTHOR]

Abstract: Though AlN nanoribbon (AlNNR) with H atom termination is a nonmagnetic semiconductor, the dangling bonds cause magnetic semimetal for zigzag edged AlNNR (ZAlNNR) with bare N edge, magnetic metal for ZAlNNR with bare Al edge or bare N and Al edges, magnetic semiconductor for armchair edged AlNNR (AAlNNR) with bare N edge or bare Al edge. Due to the strong coupling of the dangling bonds of dimeric N and Al atoms at the same edge, the AAlNNR with bare N and Al edges is still a nonmagnetic semiconductor. The magnetic moment of ZAlNNR with either bare N edge or bare Al edge is nearly half of the magnetic moment of AAlNNR with either bare N edge or bare Al edge due to its half number of the dangling bonds in per unit cell with respect to AAlNNR cases. The larger difference charge density between the majority spin and minority spin for edge bare N atoms and decaying for N sub-lattices away from edge, as well as the smaller difference charge density for edge bare Al atoms and without decaying for Al sub-lattices away from edge indicate the magnetic moment of both ZAlNNR and AAlNNR with bare N edge is larger than that of them with bare Al edge. The dangling bonds induce both ZAlNNR and AAlNNR with bare N edge a completely (100%) spin polarization at the Fermi level, indicating such structures can be utilized to construct efficient spin-polarized transport devices. [Copyright &y& Elsevier]

The spin-polarized first-principles calculations are performed to study the structural, electronic and magnetic properties of a single and two identical transition metal (TM) atoms X (X = V, Cr, Mn, Fe, Co and Ni) doped ZnS dilute magnetic semiconductors (DMS). The single V-, Cr-, Fe- and Ni-doped ZnS systems exhibit the magnetic half-metallic (HM) characters, while Mn- and Co-doped ZnS systems display magnetic semiconducting characters. For two identical TM atoms doped ZnS systems, the two identical V, Cr and Ni atoms are in a ferromagnetic (FM) coupling under the double-exchange (DE) mechanism, leading V-, Cr- and Ni-doped ZnS systems to be HM with FM coupling. While two identical Mn- and Co-doped ZnS systems are semiconductors with antiferromagnetic (AFM) coupling consisting with the superexchange (SE) mechanism. Specifically, two identical Fe atoms display a competition between the SE and DE mechanisms. The Zn 70 Fe 2 S 72 system is metal with AFM coupling at the nearest separation of two Fe atoms while HM with FM coupling at the farther separations of two Fe atoms. [ABSTRACT FROM AUTHOR]

The structural, electronic, and magnetic properties of the stoichiometric (001) surface of double perovskite Sr2FeMoO6 have been studied by using a 10-layer FeMoO4 and SrO terminated (001)-oriented slab model and the first-principles projector augmented wave potential within the generalized gradient approximation as well as taking into account the on-site Coulomb repulsive (U = 2.0 eV for Fe and 1.0 eV for Mo). An outwards relaxation is observed for several layers near surface, and the accompanying layer rumpling has a decrease tend from surface layer to inner layer. Along Fe-O-Mo-O-Fe or Mo-O-Fe-O-Mo chains, the oxygen atom is closer to the adjacent Mo atom than to the adjacent Fe atom. In FeO6 or MoO6 octahedra, the two axial TM−O bonds are not equal, and especially, the surface dangling bond makes the remaining one axial TM−O bond slightly shorter than four equally equatorial TM−O bonds. The half-metallic nature and a complete (100%) spin polarization character ensure the FeMoO4 and SrO terminated (001)-oriented slab of double perovskite Sr2FeMoO6 a potential application in spintronics devices. The Fe+3 and Mo+5 ions are still in the (3 d5, S = 5/2) and (4 d1, S = 1/2) states with positive and negative magnetic moments respectively and thus antiferromagnetic coupling via oxygen between them. There is no direct interaction between two nearest Fe-Fe or Mo-Mo pairs, whereas the hybridizations between Fe 3 d and 4 s, O 2 s and 2 p, as well as Mo 4 d, 5 s and 5 p orbitals are fairly significant. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

For the bulk and (001) surface of Ti 2 CoSn Heusler alloy, the electronic and magnetic properties in bulk and the surface effect on the structural, electronic and magnetic properties of the alloy for different terminations of (001) surface have been studied by using first-principles calculations. The spin-gapless semiconductor (SGS) ferromagnetism with the magnetic moment of 3.00 μ B / f . u . is confirmed in the bulk Ti 2 CoSn alloy with Hg 2 CuTi-type structure. For two ideal terminations (TiCo, TiSn) and three modified terminations (CoCo*, TiTi*, SnSn*), the density of states (DOS) indicates that all terminations destroy the SGS character. Furthermore, we find that the atomic magnetic moments (AMM) decrease for the most atoms on the outmost three layers due to structural relaxation of these atoms inward. Both the DOS and AMM of the central layer L 9 are similar to the corresponding bulk characters because surface effects fade out at the position of the inner layer, 12 Å below the surface. [ABSTRACT FROM AUTHOR]

The electronic structures, magnetic properties, half-metallicity and optical properties of Zn 1 - x Mo x S ( x =0.00, 0.25, 0.50, 0.75, 1.00) are studied by spin-polarized first-principles calculation. Excepting the Zn 0.5 Mo 0.5 S system with a tetragonal structure, the other systems Zn 1 - x Mo x S ( x =0.00, 0.25, 0.75, 1.00) are all in the cubic structure. The lattice constants (volumes) of the Mo doped systems are larger than those of the pure ZnS due to the atomic radius of 2.01 Å for Mo atom larger than that of 1.53 Å for Zn atom. Although pure ZnS is a nonmagnetic semiconductor with a wide band gap of 3.12 eV, due to incompletely filled Mo-4d orbital both the moderate Mo doped systems Zn 0.5 Mo 0.5 S and Zn 0.25 Mo 0.75 S are magnetic metal, especially the less Mo doped system Zn 0.75 Mo 0.25 S and the completely Mo doped system MoS are magnetic half-metal. For Zn 0.75 Mo 0.25 S system with a magnetic half-metal character as one example, the conducted spin-up channel is only contributed by the threefold degenerate t 2g ( d x y , d y z , d z x ) states due to the tetrahedral crystal field of the S atoms pushing the spin-up channel of the double degenerate e g ( d z 2 , d x 2 - y 2 ) states down below the Fermi level E F . Mo doping not only influences the shape of the original broad absorption peak ranging from 2.5 to 20 eV of pure ZnS, but also leads to two new narrow absorption peaks appeared in the ranges from 0 to 3 eV and from 33 to 43 eV. Moreover, their maximum absorption rate and the corresponding energy increase with increasing Mo content. These results are very useful for Zn 1 - x Mo x S to be applied in optical detectors and spintronics devices. [ABSTRACT FROM AUTHOR]

Adsorptions of SO 2 on Al-, Ca-, Co-, Cu-, Ge-, Ni-, and Si-doped (8, 0) boron nitride nanotube (BNNT) have been studied using first-principles approach based on density functional theory in order to exploit their potential applications as SO 2 gas sensors. The electronic properties of the BNNT-molecule adsorption adducts are strongly dependent on the dopants. The most stable adsorption geometries, adsorption energies, charge transfers, and density of states of these systems are thoroughly discussed. This work reveals that the sensitivity of (8, 0) BNNT based chemical gas sensors for SO 2 can be drastically improved by introducing appropriate dopant. Si is found to be the best choice among all the dopants. [ABSTRACT FROM AUTHOR]

The structural, magnetic, electronic and optical properties of the Zn 0.5 Cr 0.5 S ZB , Zn 0.5 Cr 0.5 S W and Zn 0.5 Cr 0.5 S RS are studied by spin-polarized first-principles calculation. After optimization Zn 0.5 Cr 0.5 S ZB system changes its original cubic structure of ZnS ZB to a tetragonal structure, while Zn 0.5 Cr 0.5 S W and Zn 0.5 Cr 0.5 S RS still remain their original hexagonal structure of ZnS W and tetragonal structure of ZnS RS , respectively. The total moments of these Cr doped ZnS systems are mainly contributed by local magnetic moments of Cr 2+ ion. Zn 0.5 Cr 0.5 S ZB , Zn 0.5 Cr 0.5 S W and Zn 0.5 Cr 0.5 S RS are all half-metal with 100% spin polarization. The Zn 0.5 Cr 0.5 S W has the biggest static dielectric constant ɛ 1 (0) and refractive index n (0). The Zn 0.5 Cr 0.5 S ZB , Zn 0.5 Cr 0.5 S W and Zn 0.5 Cr 0.5 S RS have tow absorption regions in the ranges of 0–27 eV and 41–55 eV, but the absorption width decreases for Zn 0.5 Cr 0.5 S W , Zn 0.5 Cr 0.5 S ZB and Zn 0.5 Cr 0.5 S RS successively. The results will give a guide for design and application of the Zn 0.5 Cr 0.5 S ZB , Zn 0.5 Cr 0.5 S W and Zn 0.5 Cr 0.5 S RS in spintronic devices and optical detectors. [ABSTRACT FROM AUTHOR]

From the point of view of the half-metallic character and magnetization reduction, the structural, electronic and magnetic properties of the imperfect Sr 2 FeMoO 6 compound containing seven different defects of the Fe Mo or Mo Fe antisites, Fe–Mo interchange, V Fe , V Mo , V O or V Sr vacancies have been studied by using first-principles projector augmented wave (PAW) within generalized gradient approximation (GGA) as well as taking into account on-site Coulomb repulsive interaction (GGA + U). No obvious structural changes are observed for the imperfect Sr 2 FeMoO 6 compound containing Fe Mo or Mo Fe antisites, Fe–Mo interchange or V Sr vacancy defects. However, the six (eight) nearest oxygen neighbors of the vacancy move away from (close to) V Fe or V Mo (V O ) vacancies. The half-metallic character is maintained for the imperfect Sr 2 FeMoO 6 compound containing Fe Mo antisite, V Fe , V O or V Sr vacancies, while it vanishes when Mo Fe antisite, Fe–Mo interchange or V Mo vacancy are presented. So the Mo Fe antisite, Fe–Mo interchange or V Mo vacancy defects have to be avoided in order to preserve the half-metallic character of the Sr 2 FeMoO 6 compound and thus usable in spintronics devices. In Fe Mo or Mo Fe antisites, Fe–Mo interchange cases, the spin moments of Fe (Mo) cations situated on Mo (Fe) antisites are in an antiferromagnetic coupling with those of Fe (Mo) cations on the regular sites. In V Fe , V Mo , V O or V Sr vacancies cases, a ferromagnetic coupling is obtained within each cation sublattice, while two cation sublattices are coupled antiferromagnetically. The total magnetic moments μ tot ( μ B /f.u.) of the imperfect Sr 2 FeMoO 6 compound containing seven different defects decrease in the sequence of V Sr vacancy (4.38), V Mo vacancy (3.92), V O vacancy (3.51), V Fe vacancy (3.40), Fe Mo antisite (3.40), Mo Fe antisite (3.33), Fe–Mo interchange (2.47) and the mechanisms of the saturation magnetization reduction have been discussed. [ABSTRACT FROM AUTHOR]

The electronic structures, magnetic properties, and half-metallicity of full-Heusler alloys Zr 2 CoZ (Z=Al, Ga, In, Sn) with the Hg 2 CuTi -type structure have been studied by using the first-principles projector augmented wave (PAW) potential within the generalized gradient approximation (GGA). The Zr 2 CoZ (Z=Al, Ga, In, Sn) are found to be half-metallic ferrimagnets within a certain range of the lattice constant. The total magnetic moments ( μ t ) of the Zr 2 CoZ alloys are calculated to be 2 for Z=Al, Ga, In and 3 for Z=Sn, linearly scaled with the total number of valence electrons ( Z t ) by μ t = Z t − 18 . The origin of the band gap for these half-metallic alloys is well understood. These new Zr-based Heusler alloys are the ideal candidates for spintronic devices. [ABSTRACT FROM AUTHOR]

To exploit the potential application of nitride nanotube (BNNT), the adsorption of sulfur dioxide (SO 2 ) on pristine and Mn-doped BNNT was theoretically studied using first-principles approach based on density functional theory (DFT). The most stable adsorption geometry, adsorption energy, magnetic moment, charge transfer and density of states of these systems are discussed. SO 2 molecule is weakly adsorbed on the pristine BNNT. The Mn-doped BNNT show high reactivity toward SO 2 regardless of the Mn B site or Mn N site adsorption. The larger formation energies and analysis of density of states show the SO 2 molecules are chemically bonded to Mn-doped BNNT and the covalent interaction between the SO 2 molecule and Mn atom can be formed. Therefore, the Mn-doped BNNT can be used as SO 2 gas sensor manufacturing raw materials, and it may be a potential material for nanodevice applications. [ABSTRACT FROM AUTHOR]

Based on extensive first-principles calculations, we report the equilibrium atomic configuration, mechanical and electronical properties of nonplanar oxygen-passivated armchair graphene nanoribbons (O-AGNRs) under uniaxial strain. We can get more stable and stiffer structures using uniaxial strain. The mechanical properties of the O-AGNRs such as Young’s modulus exhibits nonlinear behavior with strain, and Poisson’s ratio shows a decreasing trend with increasing tensile strain. In addition, under uniaxial strain the band gaps of the nonplanar O-AGNRs not only experience a transition between direct and indirect but also change their widths and can be classified into three families according to the ribbon width of 3 n , 3 n + 1, and 3 n + 2. [ABSTRACT FROM AUTHOR]

The first-principles projector-augmented wave (PAW) potentials within the density function theory (DFT) framework have been used to determine the geometry structures and electronic properties of the zigzag edge AlN nanoribbons (ZAlNNRs) doped with a single Si chain under generalized gradient approximation (GGA). The average Al–Si, Si–Si, Al–N, Si–N, Al–H and N–H bond lengths are 2.39, 2.16, 1.83, 1.74, 1.59 and 1.03 Å, respectively. Pure 7-ZAlNNR is an indirect semiconductor with a large band gap of 2.235 eV, while a semiconductor to metal transformation is taken place after a single Si chain substituting for a single Al–N chain at various positions. In pure 7-ZAlNNR, the HVB and LCB are mainly attributed to the edge N and Al atoms, respectively, while in a single Si chain substituting doped 7-ZAlNNR, the HVB and LCB are mainly attributed to the Si atoms. The Al–N, Al–H and Al–Si bonds are ionic bond, the Si–Si and Si–H bonds are covalent bond, the N–H and N–Si bonds are covalent bond modified ionic bond. [ABSTRACT FROM AUTHOR]

The F doping effects on the electronic structure and magnetic properties of CrO 2 have been studied using the first principles projector-augmented wave potential within the GGA+ U . The F-doped CrO 2 with low F concentration keeps a high spin polarization. Due to F doping, five different Jahn–Teller structural distortions are observed for the octahedrons around five groups Cr atoms in F-doped CrO 2 , this results from the 3 d electron orbitals are asymmetrically occupied. Compared with pure CrO 2 , the decrease of spin polarization of F-doped CrO 2 is contributed by the shift of Cr IB 3 d state towards low energy region. The impurity moment by substituting F impurities for O atoms are aligned with the host moment and the total magnetic moment increase about 1 μ B by more substituting one F impurity for one O atom, indicating that magnetic moment can be controlled by F doping. For Cr 54 O 102 F 6 , Cr IIA and Cr IIB alternately arrange in a unbroken F–Cr–F zigzag chain along the 〈 111 〉 direction in the ( 1 1 ¯ 0 ) plane, but the additional magnetic moment by substituting F impurity for O does not appear to reside on the Cr ion in the vicinity of the F impurity, but is quite diffuse due to the magnetic double-exchange interaction. [ABSTRACT FROM AUTHOR]

The structural, electronic and magnetic properties of the zigzag Si chains substituting for zigzag Al–N chains in hydrogen terminated hexagonally AlN nanoribbon with 7 zigzag Al–N chains across the ribbon width (7-ZAlNNR) have been investigated systematically using the first-principles calculations. The longer Si–Si bond length leads to a decrease (increase) in armchair (zigzag) Al–N bond length. The pure 7-ZAlNNR is a non-magnetic indirect semiconductor with a large indirect band gap of 2.979 eV. The Si chains doped 7-ZAlNNR is always metallic regardless of the Si chains doping concentrations, while the induced magnetic moment depends on the Si chains doping concentrations, increasing from 0.11 μ B for Si 2 –7-ZAlNNR to 0.45 μ B for pure 7-ZSiNR. The very low Si chains doping concentration makes the Si 1 –7-ZAlNNR a zero magnetic moment. Compared with the total DOS of the pure 7-ZAlNNR, the total DOS of the Si chains doped 7-ZAlNNR is not only broadened and shifted towards the low energy region but also transformed to metal. The magnetic moments of the Si chains doped 7-ZAlNNR are resulted from the zigzag Si chains but are not from zigzag Al–N chains because the Si–Si bond is a covalent σ bond with nonbonding π electrons while the Al–N bond is an ionic bond. Furthermore, on zigzag Si chains, the magnetic moments are mainly localized on the edge Si atoms decaying parallel (antiparallel) to the same (different) inner sub-lattices. With increasing Si chains doping concentration, both spin channels enlarge their distribution regions and thus magnetic moments. [ABSTRACT FROM AUTHOR]

The effects of a single phosphorus doping on the electronic and magnetic properties of the silicene nanoribbons (SiNRs) with both armchair edge (ASiNRs) and zigzag edge (ZSiNRs) have been studied using the first-principles projector-augmented wave potential within the density function theory framework. We analyze the formation energies, electronic band structures, charge densities and magnetic properties of the two edge shaped SiNRs with doping sites ranging from edge to center. We found that phosphorus atom preferentially substitutes at the edges of both ASiNRs and ZSiNRs. Although the pristine ASiNRs and ZSiNRs are non-magnetic semiconductor, the ASiNRs with P doping at edge site change into ferromagnetic (FM) semiconductor due to the spin splitting induced by the impurity, while the ASiNRs with P doping in inner sites change into non-magnetic metal because of the appearance of a half-filled impurity band across the Fermi level. When a P atom is doped in ZSiNRs, an antiferromagnetic (AFM) to FM transition is happened due to spin suppression at doped edge. [ABSTRACT FROM AUTHOR]

Abstract: The effect of antisite, swap and vacancy defects on the magnetic properties and spin-polarization of the full-Heusler Ti2FeAl alloy with the Hg2CuTi-type structure is studied by using the first-principles calculations within density functional theory. The perfect Ti2FeAl Heusler alloy exhibits a ferromagnetic half-metallic behavior with the total magnetic moment of 1µ Β and indirect band gap of 0.543eV. Among swap defect, only the total magnetic moment of the Ti2–Al swap defected is close to the perfect alloy. All defected structures destroy the half-metallicity and only AlTi1 and AlTi2 antisite and Fe vacancy defects maintain relatively high spin polarization. [Copyright &y& Elsevier]

Using the first-principles calculations within density functional theory, we investigate the magnetic properties and electronic structures of the Ti2MnZ (Z=Al, Ga, In, Si, Ge, Sn) alloys with the Hg2CuTi-type structure. The Ti2MnZ (Z=Al, Ga, In, Si, Ge, Sn) are found to be half-metallic ferrimagnets. The total magnetic moments (µ t ) of the Ti2MnZ alloys are calculated to be 0 for Z=Al, Ga, In and 1 for Z=Si, Ge, Sn, linearly scaled with the total number of valence electrons (Z t ) by µ t =Z t −18. The origin of the band gap for these half-metallic alloys is well understood. We expect our results to trigger further experimental interest in these alloys. [ABSTRACT FROM AUTHOR]

Abstract: Electronic structure and magnetic calculations properties of the Ti-based Heusler alloys Ti2FeSi have been studied using the first-principles projector augmented wave potential within the generalized gradient approximation taking into account the Coulomb interaction. Calculated the density of states are discussed in terms of the contribution of Ti 3d24s2, Fe 3d64s2, and Si 3s23p2 partial density of states and the spin magnetic moments were also calculated. The density of states of the Ti2FeSi compound shows the spin-up electrons are metallic, but the spin-down electrons are semiconductor with a gap of 0.612eV. Si atom shows only a small magnetic moment, but the magnetic moment of Fe atom is antiparallel to that of Ti atoms. The Ti2FeSi Heusler compound has a magnetic moment of 2μB at the equilibrium lattice constant a=6.057Å. [Copyright &y& Elsevier]

Abstract: Vacancy and doping induced magnetism in BaTiO3 perovskite is investigated by performing first-principles calculations. We demonstrate that all of the vacancies and doping induce ferromagnetism but by different mechanisms. Detailed electronic structure analysis revealed that the ferromagnetisms originate from the spin polarized Ti eg, O px, py and pz, N px and py, and Mn t2g for the O vacancy (VO), Ti vacancy (VTi), N substituting O (DN), and Mn substituting Ti (DMn), respectively. Either vacancy or doping in BaTiO3, exhibits half-metallic properties at O site, while reveals metallic properties at Ti site. The results presented here provide fundamental insights into the design of the multiferroics in conventional ferroelectrics. [Copyright &y& Elsevier]

Highlights: [•] The BaMnO3/(BaSrCa)Ti superlattice is found to be half-metallic ferromagnetic material. [•] There is no interface states at the Fermi level EF in the BaMnO3/(BaSrCa)Ti superlattice. [•] The isovalent cations substation on the A sites less influence the interfacial Mn atoms. [•] The interfacial Mn atom plays the key role in determining the electronic and magnetic properties. [ABSTRACT FROM AUTHOR]

Abstract: The detailed orbital-decomposed electronic structures of the tetragonal zirconia have been investigated by using the first-principles projector augmented wave (PAW) potential within the generalized gradient approximation (GGA) as well as taking into account the on-site Coulomb repulsive interaction (GGA+U). The deviation of the minimization energy from d z =0 to d z =±0.032 for experimental lattice constants (a=3.605Å and c=5.180Å) confirms the alternating displacement of the oxygen atoms, which causes half of the ZrO bonds stronger and the other half weaker compared with the bonds in symmetric (d z =0) zirconia. The distorted tetragonal environment of the eight oxygen anions around Zr site splits the five-fold degenerate d states of a free Zr atom into triply degenerate t2g (d xy , d yz and d zx ) states and doubly degenerate e g ( and ) states. The additional covalent character upon Zr-O ionic bonds are resulted from the hybridization between the O(2s), O(2p) and Zr(5s), triply degenerate t2g (d xy , d yz and d zx ) states of Zr(4d). The O(2s) and O(2p) states are clearly separated and no hybrid bonding states are formed. [Copyright &y& Elsevier]

Abstract: The structural, electronic and magnetic properties of the double perovskite Pb2FeReO6 have been studied by using the first-principles projector augmented wave (PAW) potential within the generalized gradient approximation (GGA) as well as taking into account the on-site Coulomb repulsive and exchange coupling interactions (GGA+U). The optimized crystal structure of the Pb2FeReO6 is a body-centered tetragonal (BCT) with a space group of I4/m and the lattice constants of a=b=5.59Å and c=7.93Å, consistent with the experimental results. The two axial transition metal and oxygen (TM–O) distances are slightly larger than the four equatorial TM–O distances and shows the existence of the Jahn–Teller structural distortion in FeO6 and ReO6 octahedra. The Fe3+ and Re5+ ions are in the states (3d5, S=5/2) and (5d2, S=1) with magnetic moments 3.929 and −0.831μ B respectively and thus antiferromagnetic (AFM) coupling via oxygen between them. The half-metallic (HM) ferromagnetic (FM) nature implies a potential application of this new compound in magnetoelectronic and spintronics devices. [Copyright &y& Elsevier]

Abstract: Under generalized gradient approximation (GGA), the structural and electronic properties of AlN and Si sheets, hydrogen terminated AlN and Si nanoribbons with hexagonal morphology and 2, 4, 6 zigzag chains across the ribbon width and the hexagonally bonded heterosheets AlNSi x (x=2, 4, and 6) consisting of hexagonal networks of AlN (h-AlN) strips and silicene sheets with zigzag shaped borders have been investigated using the first-principles projector-augmented wave (PAW) formalism within the density function theory (DFT) framework. The AlN sheet is an indirect semiconductor with a band gap of 2.56eV, while the Si sheet has a metallic character since the lowest unoccupied conduction band (LUCB) and the highest occupied valence band (HOVB) meet at one k point from Γ to Z. In the semiconductor 6-ZAlNNR, for example, the states of LUCB and HOVB at zone boundary Z are edge states whose charges are localized at edge Al and N atoms, respectively. In metallic 6-ZSiNR, a flat edge state is formed at the Fermi level E F near the zone boundary Z because its charges are localized at edge Si atoms. The hybridizations between the edge states of h-AlN strips and silicene sheets result in the appearance of border states in the zigzag borders of heterosheets AlNSi x whose charges are localized at two atoms of the borders with either bonding or antibonding π character. [Copyright &y& Elsevier]

Abstract: Under GGA, the structural, electronic properties and stabilities of four different (1×1) terminations of cubic PbTiO3 (111) surface, the directly cleaved (111)-Ti and (111)-PbO3 terminations and the constructed (111)-TiO and (111)-PbO2 ones, have been systematically studied by using projector-augmented wave method implemented in VASP. For (111)-Ti and (111)-PbO3 terminations, Ti–O bonds between the outermost two layers are enhanced after relaxation, while those between the second and the third layers are weakened. In addition, a contraction of O–O distance in surface PbO3 layer is also found for (111)-PbO3 termination. Moreover, electronic structures of both (111)-Ti and (111)-PbO2 terminations are significantly influenced by structure relaxations, and the effects of the surface on the DOS are dominantly on the Ti layers, especially the CB. For a constructed (111)-TiO termination, the relaxation results show both Ti–O bonds between the outermost two layers and those between the second PbO3 layer and the third Ti layers are enhanced. For a constructed (111)-PbO2 termination, Ti–O bonds between the outermost two layers are also enhanced as in the (111)-TiO termination, however, inequivalent Ti–O bonds between the second layer Ti atom and the third layer O atoms are found, with two bonds expanding and the other one contracting. Results of electronic structure calculations show these two constructed terminations are all insulating and changes of DOS originate dominantly from modifications of surface compositions. Furthermore, it is found that for all four different (111) terminations, the movements of the cation and/or anion on the outermost layer along the surface normal direction after relaxation all result in a reduction of the space electric field. In O and Pb external environments, it is predicted that (111)-PbO2 termination is the most stable one in O- and Pb-rich environments, however, the (111)-Ti termination is stable one in O- and Pb-poor conditions. The (111)-TiO termination also shows a stability domain in moderate O and Pb environments. [Copyright &y& Elsevier]

By using first-principles calculations, we have systematically investigated the structural and electronic properties of an infinite linear monatomic Cu chain with an adsorbed CO molecule. We find that the bridge geometry is energeticabsally favored not only when the Cu–Cu bond below the molecule is unstretched, but also for a wide range of d Cu–Cu up to about 4.20 Å, while the substitutional geometry is favored only in the hyperstretched situation d Cu–Cu >4.80 Å. Charge density differences point out the electron transfer is from the Cu atoms to the adsorbed CO molecule. The binding mechanism of CO to Cu chain can be described by the Blyholder’s model, in terms of σ-donation of electron density from the nonbonding CO-5σ orbital into empty metal orbitals and π-backdonation from the occupied metal d orbitals to empty CO-2π ⁎ orbital. The donation/backdonation process leads to the formation of bonding/antibonding pairs, 5σ b /5σ a and 2π b ⁎ /2π a ⁎ , with the 5σ a lying above E f and the 2π b ⁎ below E f . [ABSTRACT FROM AUTHOR]

Abstract: First-principles nonmagnetic calculations reveal a metallic character in zigzag SiGe nanoribbons (ZSiGeNRs) regardless of their width. The partial DOS projected onto the Si and Ge atoms of ZSiGeNR shows that a sharp peak at the Fermi level is derived from the edge Si and Ge atoms. The charge density contours show the Si–Ge bond is covalent bond, while for the Si–H bond and Ge–H bond, the valence charges are strongly accumulated around H atoms due to their stronger 1s potential and the higher electronegativity of 2.20 than that of 1.90 for Si atom and 2.01 for Ge atom, so that a significant charge transformation from Si or Ge atoms to H atoms and thus an ionic binding feature. Spin–polarization calculations show that the band structures of ZSiGeNR are modified by the dangling bonds. Compared with perfect ZSiGeNR which is a ferrimagnetic semiconductor, the bands of the ZSiGeNRs with bare Si edge, bare Ge edge, and bare Si and Ge edges shift up and nearly flat extra bands appear at the Fermi level. The ZSiGeNR with bare Si edge or bare Ge edge is a ferrimagnetic metal, while ZSiGeNR with bare Si and Ge edges is a nonmagnetic metal. [Copyright &y& Elsevier]

Abstract: Using the first-principles calculation, we investigate the structural and electromagnetic properties of the zigzag edge Si nanoribbons (ZSiNRs) decorated with double C chains. The results show that double C chains decorated ZSiNRs are always metallic independent of the ribbon width. The defect states contributed from double C chains are composed of two degenerated bands across the Fermi level. The perfect ZSiNR has a FM ground state, while double C chains decorated one have an AFM ground state. The C chains are always close to straight ones thereby resulting in a transverse contraction near the C chains and thus the ribbon width. The C–Si bond displays an ionic binding feature and the C–H bond is a typical covalent one because of the electronegativity and the bound force difference between H, C and Si atoms. [Copyright &y& Elsevier]

Abstract: The structural and electronic properties of zigzag edge silicene nanoribbons (ZSiNRs) doped with a single C chain have been studied by first-principles projector augmented wave (PAW) potential within the density function theory (DFT) framework. The results show that the C chain is almost close to a straight one which results in a transverse contraction near C chain and thus the ribbon width. The C–Si and Si–H bonds are typical ionic bonds while the C–H bond is a covalence bond. ZSiNRs doped with a single C chain are all metallic independent of the position of the C chain. All these results have been explained satisfactory from the electronegativity difference and the bound force to the electrons because of the atom radius difference between the elements. [Copyright &y& Elsevier]

Abstract: Using the first-principles calculations, we investigate the structural and electronic properties of the armchair silicene nanoribbons (ASiNRs) with a monovacancy or a divacancy. We find that either a monovacancy or a parallel oriented divacancy changes a direct semiconductor ASiNR to an indirect one, while a slanting oriented divacancy changes it to a metallic character. However, neither a monovacancy nor a divacancy can change the nonmagnetic character of the ASiNR even the metallic ASiNR with a slanting oriented divacancy. Furthermore, the optimized vacancy structure and the electronic properties are independent of the vacancy positions relative to the edge of the nanoribbon. [Copyright &y& Elsevier]

Abstract: Under the generalized gradient approximation (GGA), the magnetic and electronic properties have been investigated for a Fe atom chain wrapped in armchair (n,n) carbon nanotubes (CNTs) (2≤ n ≤6)) by using the first-principles projector-augmented wave (PAW) potential within the density function theory (DFT) framework. After simply moving the Fe atom chain parallel to tube axis to make Fe atom locates on the perpendicular of the tube wall through the center of a hexagon by carbon–carbon bonds, all Fe@(n,n) systems including the narrow Fe@(2,2) and Fe@(3,3) systems exhibit metallic character and the Fe atom chain maintains its magnetic moment. Total density of states (DOS) and projected densities of states (PDOS) analyses show that the spin polarization and the magnetic moment of Fe@(n,n) systems come mostly from the Fe atom chain. And with increasing n and thus tube diameter, the difference between the minority spin and the majority spin at the Fermi level increases for the PDOS onto Fe atom and thus for the DOS of Fe@(n,n) systems. This trend is also indicated quantitatively by the magnetic moment on Fe atom and spin polarization for Fe@(n,n) systems. The higher magnetic moment and spin polarization of the Fe@(6,6) system show it can be used as magnetic nanostructure possessing potential current and future applications in permanent magnetism, magnetic recording, and spintronics. [ABSTRACT FROM AUTHOR]

Abstract: Under the generalized gradient approximation (GGA), the structural, electronic and magnetic properties of zigzag BN nanoribbon (ZBNNR) with period vacancy located at different sites across ribbon width are investigated by using the first-principles projector-augmented wave (PAW) potential within the density function theory (DFT) framework. It is found that the formation of the N vacancy is easier than that of the B vacancy at each equivalent geometrical site and both of them are endothermic. Furthermore, the inward relaxations of the three nearest B atoms around N vacancy are smaller than the outward relaxations of the three nearest neighbor N atoms around the B vacancy. Except for the N vacancy at N side and the B vacancy at B side, the N or B vacancies at other sites induce magnetic moment and spin polarization implying such vacancy defected ZBNNRs can be utilized to construct efficient spin-polarized transport devices. [ABSTRACT FROM AUTHOR]