3d过渡金属Co掺杂核壳结构硅纳米线的第一性原理研究

基于密度泛函理论的第一性原理计算,研究了横截面为五边形和六边形的核壳结构硅纳米线的过渡金属Co原子替代掺杂.通过比较形成能发现,核心位置掺杂、壳层单链掺杂以及外壳层全替代掺杂的硅纳米线都具有稳定性,其中核心位置掺杂结构的稳定性最高.掺杂体系均呈现金属性,随着掺杂浓度的增加,电导通道数增加.Co原子掺杂的硅纳米线呈现铁磁性,具有磁矩.Bader电荷分析表明,电荷从Si原子转移至过渡金属Co原子.与自由态时过渡金属Co原子的磁矩相比,体系中Co原子的磁矩有所降低,这主要是由Co原子4s轨道向3d/4p轨道的电荷转移以及4s,3d,4p的上自旋电子转移至下自旋导致的.     

Effect of codoping with C or N on electronic structures and magnetic properties of ZnO:Cu

Using first-principles calculations based on density functional theory, we investigated systematically the electronic structures and magnetic properties of ZnO:Cu. The results indicate that Cu-doped ZnO prefers a ferromagnetic ground state and behaves like a half-metallic ferromagnet. The magnetic moment mainly localizes at Cu atom and the rest mainly comes from the spin polarized O atoms. It has been found that the ferromagnetic stability can be enhanced slightly by substituting an oxygen atom with one N atom; while the ferromagnetic stability can be weakened by replacing one O atom with a C atom. Due to absence of magnetic ion and the 100% spin polarization of the carriers in ZnO:Cu, one can expect that Cu-doped ZnO would be a useful half-metallic ferromagnet both in practical application and in theoretical studies.     

Magnetic properties of Ni doped gallium nitride with vacancy induced defect

Investigations have been carried out to study the ferromagnetic properties of transition metal (TM) doped wurtzite GaN from first principle calculations using tight binding linear muffin-tin orbital (TBLMTO) method within the density functional theory. The present calculation reveals ferromagnetism in nickel doped GaN with a magnetic moment of 1.13 μ_B for 6.25% of Ni doping and 1.32 μ_B for 12.5% of nickel doping, there is a decrease of magnetic moment when two Ni atoms are bonded via nitrogen atom. The Ga vacancy (V_Ga) induced defect shows ferromagnetic state. Here the magnetic moment arises due to the tetrahedral bonding of three N atoms with the vacancy which is at a distance of 3.689 Å and the other N atom which is at a distance of 3.678 Å .On the other hand the defect induced by N vacancy (V_N) has no effect on magnetic moment and the system shows metallic character. When Ni is introduced into a Ga vacancy (V_Ga) site, charge transfer occur from the Ni ‘d’ like band to acceptor level of V_Ga and formed a strong Ni–N bond. In this Ni–V_Ga complex with an Ni ion and a Ga defect, the magnetic moment due to N atom is 0.299 μ_B .In case of Ni substitution in Ga site with N vacancy, the system is ferromagnetic with a magnetic moment of 1 μ_B.     

Mechanism of ferromagnetism in(Fe,Co)-codoped 4H-SiC from density functional theory

First-principles calculations are performed to investigate the electronic structures and magnetic properties of(Fe, Co)-codoped 4H-SiC using the generalized gradient approximation plus Hubbard U method. We find that 4H-SiC doped with an isolated Fe atom and an isolated Co atom produces a total magnetic moment of 5.98 μ_B and 6.00 μ_B respectively. We estimate T_C of about 263.1 K for the(Fe, Co)-codoped 4H-SiC system. We study ferromagnetic and antiferromagnetic coupling in(Fe, Co)-codoped 4H-SiC. Ferromagnetic behavior is observed.The strong ferromagnetic couplings between local magnetic moments can be attributed to p–d hybridization between Fe, Co and neighboring C. However, the(Fe, Co, V_(Si))-codoped 4H-SiC system shows antiferromagnetic coupling when an Si vacancy is introduced in the same 4H-SiC supercell. The results may be helpful for further study on transition metal-codoped systems.     

Magnetism of single-walled silicon carbide nanotubes doped by boron,nitrogen and oxygen

We calculated, using spin polarized density functional theory, the electronic properties of zigzag (10,0) and armchair (6,6) semiconductor silicon carbide nanotubes (SiCNTs) doped once at the time with boron, nitrogen, and oxygen. We have looked at the two possible scenarios where the guest atom X (B, N, O), replaces the silicon X_Si, or the carbon atom X_C, in the unit cell. We found that in the case of one atom B @ SiCNT replacing a carbon atom position annotated by B_C exhibits a magnetic moment of 1 μ_B/cell in both zigzag and armchair nanotubes. Also, B replacing Si, (B_Si), induce a magnetic moment of 0.46 μ_B/cell in the zigzag (10,0) but no magnetic moment in armchair (6,6). For N substitution; (N_C) and (N_Si) each case induce a magnetic moment of 1 μ_B/cell in armchair (6,6), while N_Si give rise to 0.75 μ_B/cell in zigzag (10,0) and no magnetic moment for N_C. In contrast the case of O_C and O_Si did not produce any net magnetic moment in both zigzag and armchair geometries.     

Structural and electronic properties of boron-doped double-walled silicon carbide nanotubes

The effects of boron doping on the structural and electronic properties of (6,0)@(14,0) double-walled silicon carbide nanotube (DWSiCNT) are investigated by using spin-polarized density functional theory. It is found that boron atom could be more easily doped in the inner tube. Our calculations indicate that a Si site is favorable for B under C-rich condition and a C site is favorable under Si-rich condition. Additionally, B-substitution at either single carbon or silicon atom site in DWSiCNT could induce spontaneous magnetization.     

Magnetism in transition-metal-doped silicon nanotubes

Using first-principles density functional calculations, we show that hexagonal metallic silicon nanotubes can be stabilized by doping with 3d transition metal atoms. Finite nanotubes doped with Fe and Mn have high local magnetic moments, whereas Co-doped nanotubes have low values and Ni-doped nanotubes are mostly nonmagnetic. The infinite Si24Fe4 nanotube is found to be ferromagnetic with nearly the same local magnetic moment on each Fe atom as in bulk iron. Mn-doped nanotubes are antiferromagnetic, but a ferrromagnetic state lies only 0.03 eV higher in energy with a gap in the majority spin bands near the Fermi energy. These materials are interesting for silicon-based spintronic devices and other nanoscale magnetic applications.     

Effect of point defects on electronic and magnetic properties of single-layer SiO

Based on spin-polarised density functional theory calculations, we investigated the effect of point defects on electronic and magnetic properties of the single-layer (SL) asymmetric washboard silicon oxide (aw-SiO). The SL-aw-SiO is a counterpart of black phosphorene, and a new candidate of two-dimensional material family. This structure is dynamically and thermally stable and is a nonmagnetic semiconductor with a direct band gap. We found that single vacancy and divacancy give rise to significant change in the electronic and magnetic properties of SL-aw-SiO. The band gap of aw-SiO can be tuned by the substitution of Si atom instead of O atom, the antisite defect, the O atom vacancy and two atom vacancies. In addition, impurity states due to the defects can occur in the band continua and hence the band gap of aw-SiO is reduced. Having an integer magnetic moment, SL-aw-SiO upon Si vacancy and by substitution of O atom instead of Si atom may display half-metallic features.     

聚铜络合物[Cu(L)μ-1,3-N3]n(ClO4)n的密度泛函计算及磁性研究

基于广义梯度近似密度泛函和全势能线性缀加平面波方法,本文对聚铜络合物[Cu(L)μ-1,3-N3]n(ClO4)n(其中L=tridentate Schiff base为三齿席夫基)的态密度和磁矩进行了计算.磁矩计算结果表明:①该聚铜络合物晶体格子的总磁矩为1.00 μB;②中心铜原子(离子)具有最大的原子磁矩,为0.531 μB;③铜原子和它周围最邻近的氮原子的原子磁矩是该聚铜络合物晶体格子总磁矩的主要来源.通过对中心铜原子及其最邻近氮原子的自旋态密度图进行分析,得出了铜原子和它周围最邻近氮原子的磁性主要分别来源于它们的d轨道和p轨道,同时还发现了中心铜离子的d轨道与叠氮末端氮原子的p轨道之间存在杂化现象, 以及中心铜离子向叠氮末端氮原子的自旋退局域化现象.自旋退局域化效应通过叠氮这一旁道使相邻两中心铜离子发生铁磁性相互作用.     

First-principle study on magnetic properties of Mn/Fe codoped ZnS

We studied the magnetic properties of Mn/Fe codoped ZnS comparatively with and without defects using first-principle calculation. The calculated results indicate that the Mn/Fe codoped ZnS system tends to stabilize in a ferrimagnetic (FiM) configuration. To obtain a ferromagnetic (FM) configuration, we consider the doped system with defects, such as S or Zn vacancy. The calculated results indicate that the doped system with Zn vacancy favors FiM states. Although the FM states of the doped system with S vacancy are more stable than the FiM states in negative charge states, the FM states are not stable enough to exist. Finally, we replaced an S atom by a C atom in the doped system. The C atom prefers to substitute the S atom connecting Mn and Fe atoms. The formation energy of this defect is −0.40 eV, showing that Mn/Fe/C codoped ZnS can be fabricated easily by experiments. Furthermore, the FM state was lower in energy than the FiM state by 114 meV. Such a large energy difference between the FM and FiM states implies that room temperature ferromagnetism could be expected in such a system.     

Electronic and magnetic properties of silicene nanoflakes by first-principles calculations

The geometric, electronic, and magnetic properties of silicene nanoflakes (SiNFs) and corresponding two-dimensional (2D) framework assembled by SiNFs are studied by first-principles calculations. We find that the hexagonal SiNFs exhibit semiconducting behavior, while the triangular SiNFs is magnetic. Although the triangular SiNFs linked directly is antiferromagnetic, the system linked with an odd-number Si chains can exhibit ferromagnetic (FM) behavior, which is ascribed to anti-parallel spin rule on Si atoms, consistent with the Lieb–Mattis criterion. More interestingly, the 2D framework composed of triangular SiNFs linked by a Si atom shows a half-metallic character with an integer magnetic moment. These results provide a better understanding for silicene-based nanoflakes, and expect to pave an avenue to assemble FM silicon materials in spintronics.     

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     

Electronic properties of a silicon carbide nanotube under uniaxial tensile strain: a density function theory study

The electronic properties of an armchair (4,4) single-walled silicon carbide nanotube (SWSiCNT) with the length and diameter of 22.4 and 6.93 Å, respectively under different tensile strains are investigated by density functional theory (DFT) calculation. The change of highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO–LUMO) gap of the nanotube has been observed during the elongation process. Our results show that the gap will significantly decrease linearly with the increase of axial strain. Two different slopes are found before and after an 11% strain in the profiles of the HOMO–LUMO gap. The radial buckling has been performed to investigate the radial geometry of nanotube. The partial density of states (PDOS) of two neighboring Si and C atoms of the nanotube are further studied to demonstrate the strain effect on the electronic structure of SiC nanotube. The PDOS results exhibit that the occupied states of Si atom and the unoccupied states of C atom are red-shifted and blue-shifted under stretching, respectively. Mulliken charge analysis reveals that Si and C atoms will become less ionic under the larger strain. The electron differences of silicon carbide nanotube (SiCNT) on tensile loading are also studied.     

Theoretical study of the magnetic properties of ordered vacancies in 2D hexagonal structures: Graphene, 2D-SiC,and h-BN

The magnetic properties of vacancies in 2D hexagonal structures—graphene and 2D-SiC and h-BN monolayers—have been studied. It has been found that a local magnetic moment exists in all listed systems in the presence of vacancies. However, in 2D hexagonal silicon carbide, the local magnetic moment appears only in the presence of silicon vacancy. In addition, the effect of the distance between vacancies in a monolayer on transitions between the ferromagnetic and antiferromagnetic states has been revealed.     

5d过渡金属原子掺杂氮化铝纳米管电子结构、磁性性质的第一性原理计算

采用基于密度泛函理论(DFT)的第一性原理计算方法, 研究了5d过渡金属原子(Lu、Hf、Ta、W、Re、Os、Ir、Pt、Au、Hg)取代AlN纳米管(AlNNTs)中的铝原子或氮原子时体系的几何结构、电子结构和磁性性质; 并且以理想AlN纳米管(AlNNTs)、Al缺陷体系(VAl)和N缺陷体系(VN)的结果作为对比. 研究发现: 5d 原子取代Al(Al5d)时体系的局域对称性接近于C3v, 但是取代N(N5d)时体系的局域对称性偏离C3v对称性较大; 当掺杂的5d元素相同时, Al5d的成键能比N5d的成键能大; 当掺杂体系相同时(Al5d或N5d), 其成键能基本上随着5d原子的原子序数的增大而降低; 掺杂体系中出现了明显的杂质能级, 给出了态密度等结果; 不同掺杂情况的磁矩不同, 总磁矩呈现出较强的规律性. 利用C3v对称性和分子轨道理论解释了过渡金属原子取代Al时杂质能级的产生和体系磁性的变化规律.     

5d过渡金属原子掺杂氮化铝纳米管电子结构、磁性性质的第一性原理计算

采用基于密度泛函理论(DFT)的第一性原理计算方法, 研究了5d过渡金属原子(Lu、Hf、Ta、W、Re、Os、Ir、Pt、Au、Hg)取代AlN纳米管(AlNNTs)中的铝原子或氮原子时体系的几何结构、电子结构和磁性性质; 并且以理想AlN纳米管(AlNNTs)、Al缺陷体系(VAl)和N缺陷体系(VN)的结果作为对比. 研究发现: 5d 原子取代Al(Al5d)时体系的局域对称性接近于C3v, 但是取代N(N5d)时体系的局域对称性偏离C3v对称性较大; 当掺杂的5d元素相同时, Al5d的成键能比N5d的成键能大; 当掺杂体系相同时(Al5d或N5d), 其成键能基本上随着5d原子的原子序数的增大而降低; 掺杂体系中出现了明显的杂质能级, 给出了态密度等结果; 不同掺杂情况的磁矩不同, 总磁矩呈现出较强的规律性. 利用C3v对称性和分子轨道理论解释了过渡金属原子取代Al时杂质能级的产生和体系磁性的变化规律.     

First-principles study on the magnetic property of C-doped wurtzite ZnS

We have studied the structure, electronic and magnetic properties of wurtzite (WZ) ZnS semiconductor doped with one or two C atoms using first-principles calculations. The moderate formation energy implied that C-doped ZnS could be fabricated experimentally. The total magnetic moment of the 72 atom super cell was 2.02μB, mainly due to the 2p component of the C atom. Electronic structures showed ZnS doped with C atom was p-type half-metallic ferromagnetic (FM) semiconductor and hole mediation was responsible for the ferromagnetism. The large energy difference (154 meV) between the FM and antiferromagnetic (AFM) state implied room-temperature ferromagnetism for C-doped WZ ZnS, which has great potential in spintronic devices.     

Transport properties of boron-doped single-walled silicon carbide nanotubes

The doped boron (B) atom in silicon carbide nanotube (SiCNT) can substitute carbon or silicon atom, forming two different structures. The transport properties of both B-doped SiCNT structures are investigated by the method combined non-equilibrium Green’s function with density functional theory (DFT). As the bias ranging from 0.8 to 1.0 V, the negative differential resistance (NDR) effect occurs, which is derived from the great difficulty for electrons tunneling from one electrode to another with the increasing of localization of molecular orbital. The high similar transport properties of both B-doped SiCNT indicate that boron is a suitable impurity for fabricating nano-scale SiCNT electronic devices.     

Electronic structure and magnetic properties of substitutional transition-metal atoms in GaN nanotubes

The electronic structure and magnetic properties of the transition-metal(TM) atoms(Sc–Zn, Pt and Au) doped zigzag GaN single-walled nanotubes(NTs) are investigated using first-principles spin-polarized density functional calculations. Our results show that the bindings of all TM atoms are stable with the binding energy in the range of 6–16 eV. The Sc- and V-doped GaN NTs exhibit a nonmagnetic behavior. The GaN NTs doped with Ti, Mn, Ni, Cu and Pt are antiferromagnetic. On the contrary, the Cr-, Fe-, Co-, Zn- and Au-doped GaN NTs show the ferromagnetic characteristics. The Mn- and Codoped GaN NTs induce the largest local moment of 4μB among these TM atoms. The local magnetic moment is dominated by the contribution from the substitutional TM atom and the N atoms bonded with it.     

Cr掺杂ZnO纳米线电子性质和磁性质

本文采用第一性原理密度泛函理论系统的研究了Cr原子单掺杂和双掺杂两种尺寸ZnO纳米线的电子性质和磁性质.所有掺杂纳米线的形成能都比纯纳米线的形成能低,表明掺杂增强了纳米线的稳定性.研究发现Cr原子趋于替代纳米线表面的Zn原子.所有掺杂纳米线都显示了金属性.纳米线的总磁矩主要来源于Cr原子3d轨道的贡献.由于杂化,相邻的O原子和Zn原子也产生了少量自旋.在超原胞内,Cr和O原子磁矩反平行排列,表明它们之间是反铁磁耦合.表面双掺杂纳米线铁磁态能量比反铁磁态能量低149 meV,表明Cr掺杂ZnO纳米线可能获得室温铁磁性.