过渡金属TM(V,Cr,Mn)掺杂ZnS的电子结构和磁性

采用基于密度泛函理论(DFT)的第一性原理赝势平面波方法,对过渡金属V、Cr、Mn 掺杂ZnS的超晶胞体系进行了几何结构优化,计算了晶格常数、电子结构与磁学性质。研究结果表明：掺入V,Cr后,ZnS表现出明显的半金属性,而掺入Mn后,半金属性不明显;掺入过渡金属TM(V,Cr,Mn)后系统产生的磁矩主要有杂质的3d态电子贡献,且磁矩的大小与过渡金属的电子排布有关。     

Mn掺杂GaN稀磁半导体的电磁特性研究

采用基于密度泛函理论的第一性原理平面波超软赝势法计算了不同浓度Mn掺杂GaN(Ga1-xMnxN,x=0.0625和0.1250)的晶格常数、能带结构和态密度,分析比较了掺杂前后GaN的电子结构和磁性.结果表明:Mn掺入后体系仍为直接带隙半导体,带隙宽度随Mn含量的增加逐步增大.Mn掺杂GaN均使得N2p与Mn3d轨道杂化,产生自旋极化杂质带,自旋向上的能带占据费米面,掺杂后的Ga1-xMnxN表现为半金属铁磁性,适合自旋注入;随着Mn掺杂浓度的增加,体系的半金属性有所增强.     

Mn掺杂GaN稀磁半导体的电磁特性研究

采用基于密度泛函理论的第一性原理平面波超软赝势法计算了不同浓度Mn掺杂GaN（Ga1-xMnxN, x=0.0625和0.1250）的晶格常数、能带结构和态密度,分析比较了掺杂前后GaN的电子结构和磁性。结果表明：Mn掺入后体系仍为直接带隙半导体,带隙宽度随Mn含量的增加逐步增大。Mn掺杂GaN均使得N 2p与Mn 3d轨道杂化,产生自旋极化杂质带,自旋向上的能带占据费米面,掺杂后的Ga1-xMnxN表现为半金属铁磁性,适合自旋注入;随着Mn掺杂浓度的增加,体系的半金属性有所增强。     

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.     

Structural, electronic and magnetic properties of the 3d transition metal-doped GaN nanotubes

We have performed first-principles calculations on the structural, electronic and magnetic properties of seven different 3d transition-metal (TM) impurity (V, Cr, Mn, Fe, Co, Ni and Cu) doped armchair (5,0) and zigzag (8,0) gallium nitride nanotubes (GaNNTs). The results show that there is distortion around 3d TM impurities with respect to the pristine GaNNTs for 3d TM-doped (5,5) and (8,0) GaNNTs. The change of total magnetic moment follows Hund’s rule for 3d TM-doped (5,5) and (8,0) GaNNTs, respectively. The total density of states (DOS) indicates that Cr-, Mn-, Fe- and Ni-doped (5,5) GaNNTs as well as Cr-, Mn-, Ni- and Cu-doped (8,0) GaNNTs are all half-metals with 100% spin polarization. The study suggests that such TM-doped nanotubes may be useful in spintronics and nanomagnets.     

The evolution of electronic configuration and magnetic characterization of Fe<Subscript>9</Subscript>Ni<Subscript>1</Subscript>, Fe<Subscript>8</Subscript>Ni<Subscript>2</Subscript> alloy in theoretical calculation

To analyze the origin of the magnetic enhancement of Fe-Ni alloy, the electronicconfigurations and magnetic properties were investigated using density functional theorybased on the first-principle. The supercell (5 × 1 × 1) of Fe,Fe₉Ni₁ and Fe₈Ni₂ were constructed. Thedefect formation energy, band structure, density of states and electron density differencewere calculated. The results showed that Ni doping changed the electronic configuration ofFe atoms, resulting in the enhancement of spin polarization of Fe and the larger Bohrmagnetic moment in Fe-Ni alloys (Fe₉Ni₁). The results showed thatthe charge transfer and the atomic spacing between Fe atoms and the dopant Ni atoms playedan important role in determination of magnetic moment. The value of Fe supercell(5 × 1 × 1), Fe₉Ni₁ and Fe₈Ni₂ were 23.14,23.34 and 22.61μ _B, respectively.     

Electronic transport for impurity-doped armchair-edge graphene nanoribbons

We investigate the electronic transport for an impurity-doped armchair-edge graphene nanoribbon (AGNR), with 7 or 8 dimer lines along zigzag direction, sandwiched between two normal leads. By using the standard nonequilibrium Green’s function technique, it is demonstrated that, the impurity influence on the transport properties for system with semiconducting 7-AGNR system is more sensitive than that for one with metallic 8-AGNR system in the vicinity of the impurity energy level. In particular, in the absence of impurity the density of states (DOS) and linear conductance G possess a small zero value interval for 7-AGNR system and a large nonzero plateau for 8-AGNR one, respectively. Interestingly, as impurity included the DOS and G show a single sharp resonant peak around the impurity energy level for 7-AGNR system due to resonant tunneling, while a small dip appears in the same position for 8-AGNR system due to the antiresonance states. Moreover, we have also inspected the behavior of the differential conductance upon varying the impurity concentration for the systems. The findings here may suggest it is more favorable to fabricate an electric switch with high on-off ratio by using an impurity-assisted semiconducting AGNR.     

Half-Heusler合金Cu1-xFexMnSb的电子结构和反铁磁-铁磁相变

基于密度泛函理论（DFT）,使用局域密度近似（LDA）研究了Heusler合金Cu1-xFexMnSb的电子结构和反铁磁-铁磁相变。研究发现,两种磁状态下的合金晶格常数随掺杂浓度x变化很好地满足Vegard定理。当x>0.5时,铁磁态合金的总磁矩很好地符合SP规律,然而当x<0.5时,却发生了明显的偏离。由于整个体系存在RKKY和超交换磁耦合的竞争,因而在x=0.25时,我们观察到了独特的反铁磁—铁磁相变。进一步的态密度分析发现,Cu的掺杂浓度可以有效调整铁磁态合金的费米面位置,并且反铁磁态合金由于不同自旋方向的Mn原子的分波态密度相互补偿,总态密度形成了几乎完全对称的自旋向上带和自旋向下带。     

Half-Heusler合金Cu1-xFexMnSb的电子结构和反铁磁-铁磁相变简

基于密度泛函理论(DFT),使用局域密度近似(LDA)研究了Heusler合金Cu1-xFex MnSb的电子结构和反铁磁-铁磁相变.研究发现,两种磁状态下的合金晶格常数随掺杂浓度x变化很好地满足Vegard定理.当x0.5时,铁磁态合金的总磁矩很好地符合SP规律,然而当x0.5时,却发生了明显的偏离.由于整个体系存在RKKY和超交换磁耦合的竞争,因而在x=0.25时,我们观察到了独特的反铁磁—铁磁相变.进一步的态密度分析发现,Cu的掺杂浓度可以有效调整铁磁态合金的费米面位置,并且反铁磁态合金由于不同自旋方向的Mn原子的分波态密度相互补偿,总态密度形成了几乎完全对称的自旋向上带和自旋向下带.     

Screening of Local Magnetic Moment by Electrons of Disordered Graphene

Based on the Anderson impurity model and self-consistent approach, we investigate the condition for the screening of a local magnetic moment by electrons in graphene and the influence of the moment on electronic properties of the system. The results of numerical calculations carried out on a finite sheet of graphene show that when the Fermi energy is above the single occupancy energy and below the double occupancy energy of the local impurity, a magnetic state is possible. A phase diagram in a parameter space spanned by the Coulomb energy U and the Fermi energy is obtained to distinguish the parameter regions for the magnetic and nonmagnetic states of the impurity. We find that the combined effect of the impurity and finite size effect results in a large charge density near the edges of the finite graphene sheet. The density of states exhibits a peak at the Dirac point which is caused by the appearance of the edge states localized at the zigzag edges of the sheet.     

Structural,electronic,optical,and magnetic properties of Co-doped Cu_2O

We investigate the magnetic properties of Co-doped Cu_2O. We studied first the electronic and structural properties of Cu_2O using the optimization of the lattice constant which is 4.18 . The calculated gap is found between 0.825 eV and1.5 eV, these values are in good agreement with the experimental results. The Co atoms are inserted in Cu_2O by means of the density functional theory(DFT) using LSDA, LSDA +U, and LSDA + MBJ approximations in the WIEN2 k code, based on the supercell model by setting up 12, 24, and 48 atoms in(1×1 × 2),(1 × 2 × 2), and(2 × 2×2) supercells respectively with one or two copper atoms being replaced by cobalt atoms. The energy difference between the ferromagnetic and antiferromagnetic coupling of the spins located on the substitute Co has been calculated in order to obtain better insight into the magnetic exchange coupling for this particular compound. The studied compound exhibits stable integer magnetic moments of 2 μBand 4 μBwhen it is doped with 2 atoms of Co. Optical properties have also been worked out. The results obtained in this study demonstrate the importance of the magnetic effect in Cu_2O.     

Influence of background carriers on magnetic properties of Mn-doped dilute magnetic Si

Using hybrid exchange density functional calculations we show that the type of background carriers has profound effects on magnetic interactions in Mn doped dilute magnetic Si. The p- and n-type Si were simulated by introducing an extra hole and an extra electron, respectively in the 64 atoms Si supercell. In case of p-type Si compensated by a homogeneous background potential and 1.6% Mn, the ground state is ferromagnetic, whereas other conditions remaining the same, the ground state becomes antiferromagnetic for the n-type Si. The exchange energies in Mn-doped extrinsic Si are higher by about 1 eV/Mn atom compared to the Mn doped intrinsic Si. Calculated electronic structures reveal that in p-type Si:Mn the hole localises over Mn and the short range magnetic coupling increases. Our calculations indicate that localisation of magnetic polarons at the Mn site is likely, which in turn enhances long range magnetic interaction between Mn ions and responsible for FM stabilisation. On the other hand, in the n-type host electron–electron repulsion increases within Mn–Si impurity band and the short range coupling decreases, which destroys the long range spin polarisation. These calculations explain the observed ferromagnetism in the p-type Si:Mn at higher temperatures than in the n-type Si:Mn and the magnetic moments of the systems compare well with experiments.     

First principles study on magnetic and electronic properties with rare-earth atoms doped SWCNTs

The adsorptions of rare-earth (RE) atoms on (6, 0) and (8, 0) single-walled carbon nanotubes (SWCNTs) have been investigated by using the first-principles pseudopotential plane wave method within density functional theory (DFT). The binding energy, Mulliken charge, magnetic properties, band structure and DOS were calculated and analyzed. Most of RE atoms including Nd, Sm and Eu have a magnetic ground state with a significant magnetic moment. Some electrons transfer between RE-5d, 6s and C-2p orbitals. Owing to the curvature effect, the values of binding energy for RE atoms doped (6, 0) SWCNT are lower than those of the same atoms on (8, 0) SWCNT. The pictures of DOS show that hybridizations between RE-5d, 6s states and C-2p orbitals and between RE-4f and C-2p orbitals appear near the Fermi level. Results indicate that the properties of SWCNTs can be modified by the adsorptions of RE atoms.     

Electronic and magnetic properties of NdCrSb3: A first principles study

The electronic and magnetic properties of NdCrSb₃ are calculated by the first principles full-potential linearized augmented plane wave (FP-LAPW) method based on the density functional theory (DFT). Density of states (DOS), magnetic moments and band structures of the system are presented. For the exchange and correlation energy, local spin density approximation (LSDA+U) with the inclusion of Hubbard potential U is used. Our calculation shows that the 3d state electron of Cr and 4f state electrons of Nd contribute to the total DOS and the band structures. The effective magnetic moment is found to be 5.77μ_B, which is comparable to the earlier experimental results of NdCrSb₃.     

新型稀磁半导体Mn掺LiCaP的磁电性质

采用基于密度泛函理论的第一性原理平面波超软赝势方法,对纯LiCaP、Mn掺杂LiCaP、Li过量和不足时Mn掺杂LiCaP体系进行几何结构优化,计算并分析了体系的电子结构、能带结构、态密度等.结果表明:Li1±y(Ca1-xMnx) P(x=0. 125,y=0. 125)体系均表现为100%自旋注入,材料均具有半金属亚铁磁性,半金属性稳定,磁矩较大且主要来源于Mn掺入形成的深能级杂质带. Li过量时材料的导电性得到改善,Li不足时体系的居里温度(Tc)提高,说明LiCaP半导体的磁性和电性可以分别通过Mn的掺入和Li的含量进行调控.     

基于密度泛函理论研究掺杂Pd石墨烯吸附O2及CO

基于第一性原理的密度泛函理论研究了单个O₂和CO气体分子吸附于本征石墨烯和掺杂钯(Pd)的石墨烯的体系, 通过石墨烯掺Pd前后气体分子的吸附能、电荷转移及能带和态密度的计算, 发现掺Pd后气体分子吸附能和电荷转移显著增大, 这是由于Pd的掺杂, 在本征石墨烯能带中引入了杂质能级, 增强了石墨烯和吸附气体分子间的相互作用; 氧化性气体O₂和还原性气体CO吸附对石墨烯体系能带结构和态密度的影响明显不同, 本征石墨烯吸附O₂后, 费米能级附近态密度变大, 掺Pd后在一定程度变小; 吸附还原性的CO后, 石墨烯费米能级附近态密度几乎没有改变, 表明掺杂Pd不会影响石墨烯对CO的气体灵敏度, 但由于CO对石墨烯的吸附能增大, 可以提高石墨烯对还原性气体的气敏响应速度.     

First principles study the ferromagnetic properties and electronic structure of boron doped ZnSe

Using the full-potential linearized augmented plane wave method with generalized gradient approximation, the magnetic properties and the electronic structure of the boron-doped ZnSe (zinc blende phase) are investigated. Spin polarization calculations show the magnetic moment of the 64-atoms supercell containing one B_Se (B_Zn) is 3.00 (0.015) μ_B. The density of states indicates the magnetic moments of the B_Se doped configuration mainly come from the doped boron atoms and a few from its neighboring zinc atoms. The ferromagnetic and antiferromagnetic calculations for several doped configurations suggest B_Se could induce stable ferromagnetic ground state in ZnSe hosts and ferromagnetic couplings exist between the doped boron atoms. Electronic structures show that B_Se is p-type ferromagnetic semiconductor and hole-mediated double exchange is responsible for the ferromagnetism, while the B_Zn doped configuration is n-type semiconductor. Relative shallow acceptor and donor levels indicate boron-doped ZnSe is ionized easily at working temperatures.     

Ab initio study of the (2 × 2) phase of barium on graphene

We present a first-principles density functional theory study on the structural, electronic and dynamical properties of a novel barium doped graphene phase. Low energy electron diffraction of barium doped graphene presents clear evidence of (2 × 2) spots induced by barium adatoms with BaC₈ stoichiometry. First principles calculations reveals that the phase is thermodynamically stable but unstable to segregation towards the competitive BaC₆ monolayer phase. The calculation of phonon spectrum confirms the dynamical stability of the BaC₈ phase indicating its metastability, probably stabilized by doping and strain conditions due to the substrate. Barium induces a relevant doping of the graphene π states and new barium-derived hole Fermi surface at the M-point of the (2 × 2) Brillouin zone. In view of possible superconducting phase induced by foreign dopants in graphene, we studied the electron–phonon coupling of this novel (2 × 2) obtaining λ = 0.26, which excludes the stabilization of a superconducting phase.     

第一性原理研究Co2MnSi和Co2MnGe半金属与磁性的稳定性

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,对Co2MnSi和Co2MnGe在晶格常数发生变化的情况下进行电子结构和磁矩的自旋极化计算,得到了它们的自旋态密度分布以及总磁矩和各原子磁矩。计算结果的分析表明：（1）Co2MnSi 和Co2MnGe具有半金属性质;（2）晶格常数的改变分别为-5%~ 4%和-6%~1%时,Co2MnSi 和 Co2MnGe仍保持稳定的半金属质性;（3）Co2MnSi 和Co2MnGe的总磁矩为5.00µB/formula。总磁矩主要来源于Mn和Co的原子磁矩,Si和Ge的原子磁矩对总磁矩的贡献极小而且为负值。（4）Co2MnSi 和 Co2MnGe的晶格常数变化分别为-6% ~ 6%和-7%~ 4%时,虽然各原子磁矩都发生了变化,但是它们总磁矩稳定于5.00µB/formula.