Structural,electronic and magnetic properties of Fe(1−x)Cox alloy nanowires encapsulated inside (10,0) boron nitride nanotube

The structural, electronic and magnetic properties of Fe–Co alloy nanowires encapsulated inside zigzag (10,0) boron nitride nanotube (BNNT) are investigated by ab initio calculations. Similar to pristine nanotube, the opposite directional relaxations for the N atoms (move outwards) and B atoms (move inwards) from their initial positions are observed for outside BNNT although with the Fe–Co alloy nanowires inside, but the outward relaxations of the N atoms bonding to the Fe or Co atoms are smaller due to their attractions. The combining processes of Fe–Co/BNNT composites are endothermic when Co concentration x≤0.6 and exothermic x>0.6, and the most stable Fe–Co/BNNT composite is at Co concentration x=0.8. So the semiconducting (10,0) BNNT can be used to shield the Co-rich Fe–Co nanowires. The charges are transferred from Fe–Co nanowires to BNNT and the formed Co–N bonds have covalent bond as well as slight ionic bond characters. Although (10,0) BNNT is nonmagnetic and a decrease in the magnetic moment is found after Fe–Co nanowires are encapsulated inside (10,0) BNNT, the Fe–Co/BNNT composites still have large magnetic moment, reflecting they can be utilized in magnetic storage and ultra high-density magnetic recording devices.     

含空位二维六角氮化硼电子和磁性质的密度泛函研究

基于密度泛函理论的第一性原理计算, 研究了含B原子空位(V_B), N原子空位(V_N), 以及含B–N键空位 (V_B+N)缺陷的二维氮化硼(h-BN)的电子和磁性质. 在微观结构上, V_B体系表现为在空位附近的N原子重构成等腰三角形, V_N体系靠近空穴的B 原子形成等边三角形, V_B+N体系靠近空穴处的B和N原子在h-BN平面上重构为梯形. 三种空位缺陷都使h-BN的带隙类型从直接带隙转变为间接带隙. V_B体系的总磁矩为1.0 μ_B, 磁矩全部由N原子贡献. 其中空穴周围的三个N原子磁矩方向不完全一致, 存在着铁磁性和反铁磁性两种耦合方式. 对于V_N 体系, 整个晶胞内的总磁矩也为1.0 μ_B, 磁矩在空穴周围区域呈现一定的分布. 关键词： 二维h-BN 空位 电子结构 磁性     

First-principles study on magnetism and electronic structure of V-doped rutile TiO2

We have investigated the magnetism and the electronic structure of V-doped rutile TiO₂ using the first-principles full potential linearized augmented plane-wave (FP-LAPW) method. Total energy calculations reveal that V-doped rutile TiO₂ has a stable ferromagnetic ground state. Meanwhile, the electronic structure analysis indicates that V-doped rutile TiO₂ is a half-metal within the local density approximation (LDA) while a semiconductor within the LDA + U (Hubbard coefficient). The calculated magnetic moment in V-doped rutile TiO₂ mainly arises from the V atom with a little contribution from the nearest-neighboring O atoms due to the hybridization between the V 3d states and the nearest-neighboring O 2p states.     

Electronic and optical properties of V doped AlN nanosheet: DFT calculations

Electronic and optical properties of pure and V-doped AlN nanosheet have been investigated using density functional theory, and the dielectric tensor is calculated using the random phase approximation (RPA). The results of structural calculations show that the V atoms tend to replace instead of aluminum atoms with the lowest formation energy. In addition, study of the electronic properties shows that pure AlN nanosheet is a p-type semiconductor that by increasing one V atom, it possesses the metallic properties and magnetic moment becomes Zero. Moreover, by replacing two V atoms, the half-metallic behavior with 100% spin polarization can be found, and each supercell gains a net magnetic moment of 3.99 µ_B. Optical properties like the dielectric function, the energy loss function, the absorption coefficients, the refractive index are calculated for both parallel and perpendicular electric field polarizations, and the results show that the optical spectra are anisotropic.     

First-principles study on electronic,magnetic properties and optical absorption of vanadium doped rutile TiO2

The electronic, magnetic properties and optical absorption of vanadium (V) doped rutile TiO₂ have been studied by the generalized gradient approximation GGA and GGA+U (Hubbard coefficient) approach respectively. On the one hand, we consider the influence of vanadium with different doping concentration on the electronic structure. On the other hand, we study double V atoms doped TiO₂, mainly study four V-doped TiO₂ configurations, and find the magnetic ground states are ferromagnetic state. For the TiO₂@V-V1, TiO₂@V-V3 and TiO₂@V-V4 configurations without O ion as bridge between V-V atoms, there will have a metastable state of antiferromagnetic configurations, while, for the TiO₂@V-V2 configurations with an O ion as bridge between V-V atoms, due to the existence of superexchange between V-O-V, there will only exist the ground state of ferromagnetic state and there are no other metastable configurations. Furthermore, the optical properties of V-doped TiO₂ are calculated. The results show that the V-doped TiO₂ has strong infrared light absorption and visible light absorption.     

First-principles study of single intrinsic vacancy formation and its effect on the electronic density states and magnetic moment of V-doped ZnO

We calculated the formation energy of single vacancy in V-doped ZnO in different conditions (oxygen or zinc rich) by first principles. Effect of an intrinsic vacancy on the electronic density of states and magnetic moment of V-doped ZnO (Zn₁₅VO₁₆) with and without single vacancy was also calculated. Our calculation was performed by the CASTEP program within spin-polarized GGA approximation implemented in materials studio software. The formation energy showed that oxygen vacancy inclined to stay far from vanadium (V) and zinc vacancy preferred to stay at a position near V. The calculated formation energy also showed that a zinc vacancy may automatically occur but an oxygen vacancy may not appear automatically. Vanadium doping introduced spin-polarization around Fermi level. For an energy favorable vacancy, an oxygen vacancy had little effect on the electronic density of states. A zinc vacancy made the spin-polarization peaks around Fermi level broaden and decreased their magnitude. For the magnetic moment in energy favorable configurations, an oxygen vacancy had little effect on the magnetic moment; a zinc vacancy significantly decreased the magnetic moment (as high as 63.7%). Changes in magnetic moments were consistent with electronic density of states. Our calculation may interpret various experimental magnetic moment values. Our work also provided a reference for preparing V-doped ZnO-based dilute magnetic semiconductors.     

First-Principles Study on Magnetic Properties of V-Doped ZnO Nanotubes

Electronic and magnetic properties of V-doped ZnO nanotubes in which one of Zn^2＋ ions is substituted by V^2＋ ions are studied by the first-principles calculations of plane wave ultra-soft pseudo-potential technology based on the spin-density function theory. The computational results reveal that spontaneous magnetization in Vdoped （9,0） ZnO nanotubes can be induced without p-type or n-type doping treatment, and the ferromagnetism is isotropic and independent of the chirality and diameter of the nanotubes. It is found that V-doped ZnO nanotubes have large magnetic moments and are ferromagnetic half-metal materials. Moreover, the ferromagnetic coupling among V atoms is generated by O 2p electron spins and V 3d electron spins localized at the exchanging interactions between magnetic transitional metal （TM） impurities. The appearance of ferromagnetism in V-doped ZnO nanotubes gives some reference to fabrication of a transparent ferromagnet which may have a great impact on industrial applications in magneto-optical devices.     

Structural,magnetic and optical properties of vanadium doped zinc oxide: Systematic first-principles investigations

The electronic structural, magnetic and optical properties of pure and V-doped ZnO are investigated by first-principles calculations based on the density functional theory. With the introduction of V atoms, the spin-splitting near the Fermi level leads to a net magnetic moment of the system. A significant possibility of room temperature ferromagnetism (RTFM) originated from the Ruderman–Kittel–Kassuya–Yosida (RKKY) exchange is predicted. Oxygen vacancy is positive to enhance the ferromagnetism while zinc vacancy is negative. With respect to the optical properties, the presence of V atoms was found to have an obvious influence on the transmittivity, especially in the low energy region. A slight V-doping can keep a high optical transmission and smoothly modulate the optical bandgap.     

Magnetism and electronic structure of Mn- and V-doped zinc blende ZnTe from first-principles calculations

By means of the first-principles full potential linearized augmented plane-wave method within the local density approximation for the exchange-correlation functional, we have investigated the magnetism and electronic structure of Mn- and V-doped zinc blende ZnTe. Total energy calculations show that, for high doping concentration (12.5%), ZnTe:Mn has an antiferromagnetic ground state while the ferromagnetic state is more favorable than the antiferromagnetic state for ZnTe:V. Furthermore, ZnTe with a low doping of Mn (6.25%) has a stable ferromagnetic ground state, which is in agreement with the experimental results. The calculated magnetic moment of ZnTe doped with Mn (V) mainly originates from transition metal Mn (V) atom with a little contribution from Te atom due to the hybridization between Mn (V) 3d and Te 5p electrons. Electronic structure indicates that Mn-doped ZnTe is a semiconductor, but V-doped ZnTe shows a half-metallic characteristic. We also discuss the difference between electronic and magnetic properties for ZnTe doped with 12.5% and 6.25% Mn.     

应变和C掺杂对单层BN纳米片的电子结构和磁学性质的影响

利用基于密度泛函理论的第一性原理计算方法, 研究了应变和C原子掺杂对单层BN纳米片的电子结构和磁学性质的影响. 计算结果表明未掺杂的单层BN纳米片具有宽的直接带隙, 在压缩和拉伸应变的作用下, 带隙会分别增大和减小, 但应变对带隙的调制整体效果不太明显. 单个C原子掺入BN纳米片的态密度揭示体系呈现出半金属性(Half-metallicity), 磁矩主要源于C 2p态, 而B 2p和N 2p态在极化作用下也能提供部分磁矩. 两个C原子掺入BN纳米片时, 磁性基态会随着C原子的间距发生变化: 当两C原子为最近邻(nn)和次近邻(nnn)时, 反铁磁态为磁性基态; 而当两C原子为次次近邻(nnnn)时, 铁磁态为基态, 并且其态密度也显示出半金属性.     

First-principles studies of BN sheets with absorbed transition metal single atoms or dimers: stabilities, electronic structures, and magnetic properties

BN sheets with absorbed transition metal (TM) single atoms, including Fe, Co, and Ni, and their dimers have been investigated by using a first-principles method within the generalized gradient approximation. All of the TM atoms studied are found to be chemically adsorbed on BN sheets. Upon adsorption, the binding energies of the Fe and Co single atoms are modest and almost independent of the adsorption sites, indicating the high mobility of the adatoms and isolated particles to be easily formed on the surface. However, Ni atoms are found to bind tightly to BN sheets and may adopt a layer-by-layer growth mode. The Fe, Co, and Ni dimers tend to lie (nearly) perpendicular to the BN plane. Due to the wide band gap of the pure BN sheet, the electronic structures of the BN sheets with TM adatoms are determined primarily by the distribution of TM electronic states around the Fermi level. Very interesting spin gapless semiconductors or half-metals can be obtained in the studied systems. The magnetism of the TM atoms is preserved well on the BN sheet, very close to that of the corresponding free atoms and often weakly dependent on the adsorption sites. The present results indicate that BN sheets with adsorbed TM atoms have potential applications in fields such as spintronics and magnetic data storage due to the special spin-polarized electronic structures and magnetic properties they possess.     

Tuning the electronic and magnetic properties of boron nitride nanotubes

Density Functional Theory is used to investigate the effect of altering the B/N ratio and carbon doping on the electronic and magnetic structure of zigzag, (7, 0) and armchair (5, 5) boron nitride nanotubes. The calculations indicate that increasing the boron content relative to the nitrogen content significantly reduces the band gap to a value typical of a semiconductor. Calculations of carbon doped semiconducting BN tubes, which have more boron atoms than nitrogen atoms have a net spin and a difference in the density of states at the valence band between the spin up and spin down state.     

Energetics and electronic properties of BN nanocones with pentagonal rings at their apexes

The geometric structures, energetics and electronic properties of the recently discovered BN nanocones are investigated using first-principles calculations based on the density-functional theory. We have proposed one particular structure for BN nanocones associated with the 240^° disclination, derived by the extraction of four 60^° segments, presenting as characteristic four pentagons at the apex and termination in two atoms. The cones are simulated by three clusters containing 58 B plus N atoms and additional 12 H atoms to saturate the dangling bonds at the edge. The most stable configuration is obtained when the two terminating atoms are one B and one N. For the cases where the two terminating atoms are of the same kind, the tip with B atoms is determined to have lower binding energy than with N atoms. The local densities of states of these BN nanocones are investigated and sharp states are found in the regions close (below and above) to the Fermi energy. Received 14 October 2002 / Received in final form 6 December 2002 Published online 11 February 2003 RID="a" ID="a"e-mail: ppiquini@smail.ufsm.br     

Atomic and electronic structure of single-walled BN nanotubes containing N vacancies as well as C and O substitutes of N atoms

Defective single-walled BN nanotubes of armchair- and zigzag-type chiralities with uniform diameter can be simulated using a total geometry optimization for the 1D-periodic model. For calculations, we have applied the formalism of localized Gaussian-type atomic functions using the Hamiltonian containing hybrid (DFT+HF) non-local exchange-correlation functional B3PW as implemented in CRYSTAL code. Single N vacancy as well as C and O substitutes of N atom cause an appearance of the energy levels inside the BN NT band gap accompanied by relaxation of the nearest atomic spheres closest to the point defect and electronic charge redistribution around it.     

Effect of impurities in the large Au-Au distances in gold nanowires

Experimentally obtained atomically thin gold nanowires have presented exceedingly large Au-Au interatomic distances before they break. Since no theoretical calculations of pure gold nanowires have been able to produce such large distances, we have investigated, through ab initio calculations, how impurities could affect them. We have studied the effect of H, B, C, N, O, and S impurities on the nanowire electronic and structural properties, in particular how they affect the maximum Au-Au bond length. We find that the most likely candidates to explain the distances in the range of 3.6 A and 4.8 A are H and S impurity atoms, respectively.     

Optical properties of boron-group (V) hexagonal nanowires: DFT investigation

The paper presents structural, electronic and optical properties of boron-group V hexagonal nanowires (h-NW) within the framework of density functional theory. The h-NW of boron-group V compounds with an analogous diameter of 12 Å have been designed in (1 1 1) plane. Stability analysis performed through formation energies reveal that, the stability of these structures decreases with increasing atomic number of the group V element. The band nature predicts that these nanowires are good electrical conductors. Optical behaviour of the nanowires has been analysed through absorption coefficient, reflectivity, refractive index, optical conductivity and electron energy loss spectrum (EELS), that are computed from the frequency-dependent complex dielectric function. The analysis reveals high reactivity of BP and BAs h-NWs to the incident light especially in the IR and visible ranges, and the optical transparency of BN h-NW in the visible and UV ranges.     

3d过渡金属元素掺杂Al12N12纳米线几何结构和电子性能的第一性原理研究

基于密度泛函理论的第一性原理计算方法,系统地研究了不同3d过渡金属元素(Sc、Ti、V、Cr、Mn、Fe、Co和Ni)掺杂Al₁₂N₁₂纳米线的几何结构、稳定性和电子结构.结果表明：所有掺杂体系均是热力学稳定的;掺杂Ni时体系保留了原有的非磁性间接带隙半导体特性;当掺杂其它原子(Sc、Ti、V、Cr、Mn、Fe、Co)时体系仍然保持为半导体,但带隙明显减小.掺杂过渡金属原子对于Al₁₂N₁₂纳米线的电子结构具有明显的调控作用,在能带调控和光电方面有潜在的应用前景.     

Electronic and magnetic properties of multishell Co nanowires coated with Cu

The structural, electronic, and magnetic properties of ultrathin Cu-coated Co nanowires have been studied by using empirical genetic algorithm simulations and a tight-binding spd model Hamiltonian in the unrestricted Hartree-Fock approximation. For some specific stoichiometric compositions, Cu atoms occupy the surface, while Co atoms prefer to stay in the interior, forming the perfect coated multishell structures. The outer Cu layers lead to substantial variations in the magnetic moment of interior Co atoms, depending on the structure and thickness of Cu layers. In particular, single Co atom row at the center of nanowire is found to be nonmagnetic when coated with two Cu layers. All the other Co nanowires in the coated Cu shell are still magnetic but the magnetic moments are reduced as compared with Co nanowires without Cu coating. The interaction between Cu and Co atoms induces nonzero magnetic moment for Cu atoms.     

Half-metallic silicon nanowires: first-principles calculations

From first-principles calculations, we predict that specific transition metal (TM) atom-adsorbed silicon nanowires have a half-metallic ground state. They are insulators for one spin direction, but show metallic properties for the opposite spin direction. At high coverage of TM atoms, ferromagnetic silicon nanowires become metallic for both spin directions with high magnetic moment and may have also significant spin polarization at the Fermi level. The spin-dependent electronic properties can be engineered by changing the type of adsorbed TM atoms, as well as the diameter of the nanowire. Present results are not only of scientific interest, but also can initiate new research on spintronic applications of silicon nanowires.     

Magnetic and electronic properties of zigzag BN nanoribbons with nonmetallic atom terminations: A first-principles study

The boron nitride (BN) nanosheet is an isostructural analog of graphene and can be viewed as the structure that C atoms in graphene are replaced with alternating B and N. The easily modulated band-gap of BN nanosheet by simply passivating its edge(s) makes it is promising for many potential applications in nanodevices and nanoelectronics. We further systematically theoretically study the magnetic and electronic properties of passivated-ZBNNR by nonmetallic atom(s), here. According to our calculations, all considered structures show magnetic feature, and the ZBNNRs can be metal or half-metal or semiconductor depending on the termination details. The great application-potential of the passivated-ZBNNRs is further confirmed based on our results.