(Fe1-xNix)2P电子结构与磁学特性的X射线近边吸收谱研究

利用X射线近边吸收谱对Fe₂P,Ni₂P及其掺杂物(Fe_1-xNi_x)₂P(x=01,025,05)中Fe,Ni,P的K边进行了研究.结合多重散射理论近边计算,讨论了金属原子不同位置格点3f,3g对近边谱特征的贡献,得出当Ni原子取代Fe原子时将优先占据Fe(3f)格点位置;根据第一性原理对能态的计算发现,不考虑磁性时不同格点P的pDOS未占据态电子结构与P-K近边吸收谱实验相符合;与考虑铁磁性Fe₂P 的DOS相比较后结果显示Fe₂P的磁性主要来源于Fe(3g)格点,铁磁性Ni₂P计算的Ni不同格点原子磁矩均接近于0,与它一般显顺磁性结论相一致. 关键词： X射线近边吸收谱 电子结构 多重散射理论 态密度     

Rh在单壁碳纳米管上吸附的密度泛函理论研究

本文利用密度泛函理论研究了Rh原子在（6,6）单壁碳纳米管内外的吸附行为. 通过对Rh在单壁碳纳米管上不同吸附位的吸附构型与吸附能的研究发现: Rh吸附在管内、外的洞位最稳定, 且管外吸附比在管内强. 这是由于单壁碳纳米管的卷曲效应使得管外电荷密度比管内大造成的. 态密度分析表明, 吸附在管内外的Rh原子的5s电子均转移到了4d轨道上; Rh原子4d轨道上的电子转移到了（6, 6）碳管上, 使Rh带正电, 碳管带负电. 结合能带分析表明, Rh原子吸附在管内磁性较弱, 而吸附在管外较强. 关键词： 密度泛函理论 单壁碳纳米管 Rh原子 吸附     

新超导体MgCNi3的虚晶掺杂研究

用全势线性缀加平面波方法,考虑局域自旋密度近似研究虚晶掺杂MgCNi₃的超导电性和磁性.计算了自旋极化能带结构、体弹性模量和它对压力的导数、原子磁矩m及其变化率.计算结果表明，对于电子掺杂的Mg_1-xAl_xCNi₃(0≤x≤0.5)，超导电性和磁涨落随掺杂量的增加逐渐减小.空穴掺杂的Mg_1-xNa_xCNi₃,在x＝0.12处出现铁磁相变，超导电性消失.在MgCNi₃少量空穴掺杂区域(0≤x<0.12)，表现为超导与磁涨落共存的不稳定状态. 关键词： 超导电性 能带结构 态密度 磁性     

利用密度泛函理论研究BnNi(n≤5)小团簇的结构和磁性

基于第一性原理，用密度泛函理论中的广义梯度近似方法，获得了B_nNi(n≤5)小团簇在不同自旋多重度下的几何构型，确定了最低能量结构，并计算了相应的频率、平均结合能和磁性. 结果表明：B_nNi(n≤5)小团簇最低能量结构的自旋多重度分别为2，1，2，1，2；Ni掺入B团簇后增大了其结合能；Ni原子磁矩和团簇总磁矩随团簇尺寸增大而呈现振荡趋势. 关键词： nNi小团簇')" href="#">B_nNi小团簇 自旋多重度 磁性     

接枝羧基的有限长碳纳米管电子结构的第一性原理研究

基于局域密度泛函理论，采用第一性原理方法，建立了对(5,5)型和(9,0)型有限长碳纳米管接枝羧基官能团的原子模型，通过计算其电子分布和态密度的变化，讨论羧基官能团对碳纳米管电子结构和电子输运特性的影响. 计算表明，接枝羧基的碳纳米管,其电子结构明显改变，其费米能级上的电子态密度下降；最高占据轨道上的非定域程度减弱,致使电子输运性能呈下降趋势. 关键词： 碳纳米管 密度泛函理论 电子结构     

Nb掺杂影响NiTi金属间化合物电子结构的第一性原理计算

采用基于密度泛函理论(DFT)的第一性原理平面波超软赝势方法,计算了Nb元素掺杂对B2构型NiTi金属间化合物电子结构的影响.点缺陷生成能的计算结果表明,Nb原子掺杂后,NiTi中产生Ni原子和Ti原子空位和反位点缺陷所需要的能量均明显升高;态密度计算结果表明,Nb原子掺杂后与临近原子发生了明显的s-s, p-p和d-d电子相互作用,增加了与临近原子之间的电荷密度,有利于Nb与合金原子的成键.这些由Nb掺杂所导致的NiTi电子结构和键合特征的变化均有利于促进Nb与合金原子的相互作用,在一定程 关键词： NiTi金属间化合物 点缺陷 电子结构 第一性原理计算     

NiMgn(n=1—12)团簇的第一性原理研究

采用基于密度泛函理论(DFT)中的广义梯度近似 (GGA),在考虑自旋多重度的情况下,对NiMg_n(n=1—12)团簇进行了构型优化,频率分析和电子性质计算.结果表明：n=1,2时,体系的基态为自旋三重态,n≥3时,为单重态;Ni原子掺杂使主团簇结构发生了明显变化. n≤8时,三角双锥,四角双锥结构主导着NiMg_n基态团簇的生长行为; n在9—12之间时,主团簇Mg_n+1(n=1—12)的基于三棱柱构型的基态演化行为发生了一定程度的改变;n≥6时,Ni原子陷入了主团簇内部;掺杂使体系的平均结合能增大,能隙减小;n=4,6,10是团簇的幻数;不同尺寸团簇的s, p, d轨道杂化中,Ni原子3d, 4p成分所起作用不同; NiMg₆基态结构具有很高的对称性(O_h),很好的稳定性和化学活性,能隙仅为0.25eV. 关键词： n团簇')" href="#">NiMg_n团簇 几何结构 稳定性 化学活性     

水分子链受限于单壁碳纳米管结构的密度泛函理论研究

本文采用第一性原理的密度泛函理论,主要以(6,6)Armchair型,(11,0)Zigzag型单壁碳纳米管为研究对象,研究了水分子链在碳纳米管内部吸附的稳定结构,以及结合能随其结构的变化.结果表明:当水分子链受限于碳纳米管内部时,引起碳纳米管直径收缩,这主要是由于水分子链与碳纳米管之间的氢键作用以及范德华弱相互作用所引起的.随着碳纳米管半径的增加,两种单体之间的结合能逐渐减小,但当碳纳米管半径增加至6.78时,其结合能又有所增加,这是由于在优化过程中,水分子链单体之间的氢键作用大于水分子链与碳纳米管之 关键词： 水分子链/单壁碳纳米管 密度泛函理论 结构稳定性     

Heusler合金Co2MnAl(100)表面电子结构、磁性和自旋极化的第一性原理研究

基于第一性原理计算方法系统地研究了L2₁和B2结构下的Heusler合金Co₂MnAl(100)表面原子的原子弛豫、电子结构、磁性和自旋极化行为. L2₁和B2结构的Co₂MnAl(100)表面由于Co–Mn和Co–Al的成键差异, 使得不同原子分别发生不同程度的伸缩. 与块体相比, Co和Mn原子的自旋磁矩由于表面效应而明显增大, 电子结构计算显示L2₁结构块体中的带隙被表面态破坏, 表面效应使得两种结构的CoCo端面自旋极化率降低, 但MnAl端面并未受到显著影响, 呈现了较大的自旋极化, 预测其在隧道结中可能具有很好的应用潜力.     

掺杂MgCNi3超导电性和磁性的第一性原理研究

从第一性原理出发，计算了MgCNi₃的电子能带结构.MgCNi₃中C 2p与Ni 3d轨道杂化使穿梭费米面上的Ni 3d能带表现出平面性，费米面落在态密度范霍夫奇异(vHs)峰的右坡上.vHs峰上大的电子态密度和铁磁相变点附近的自旋涨落是决定MgCNi₃超导电性的重要因素.研究了三种替代式掺杂对其超导电性和磁性的影响，发现电子掺杂使费米能级下滑到态密度较低的位置，导致体系转变为无超导电性的顺磁相；同构等价电子数的金属间化合物的轨道杂化，引起费米面上态密度的减少，降低了超导电性；而空穴掺杂使费米面向vHs峰值方向移动，虽然费米面上电子态密度增大可能提高超导电性，但增强了的Ni原子磁交换作用产生铁磁序，破坏了超导电性. 关键词： 电子结构 超导电性 磁性 掺杂     

密度泛函理论研究BnNi(n=6—12)团簇的结构和磁性

基于第一性原理,用密度泛函理论中的广义梯度近似(generalized gradient approximation,GGA)方法,在充分考虑自旋多重度的前提下,优化并得到了B_n(n=6—12)和B_nNi(n=6—12)团簇的平衡构型,按照能量最低原理确定其基态结构. B_n团簇的计算结果与已有的理论结果相一致. 当Ni原子掺杂在B_n团簇 关键词： nNi团簇')" href="#">B_nNi团簇 基态结构 磁性     

Structural,electronic and magnetic properties of hcp Fe,Co and Ni nanowires encapsulated in zigzag carbon nanotubes

The structural, electronic and magnetic properties of hcp transition metal (TM = Fe, Co or Ni) nanowires TM₄ encapsulated inside zigzag nanotubes C(m, 0) (m = 7, 8, 9, 10, 11 or 12), along with TM _n (n = 4, 10 or 13) encapsulated inside C(12, 0), have been systematically investigated using the first-principle calculations. The results show that the TM nanowires can be inserted inside a variety of zigzag carbon nanotubes (CNTs) exothermically, except from the systems TM₄@(7, 0) and TM₁₃@(12, 0) which are endothermic. The charge is transferred from TM nanowires to CNTs, and the transferred charge increases with decreasing CNT diameter or increasing nanowire thickness. The magnetic moments of hybrid systems are smaller than those of the freestanding TM nanowires, especially for the atoms on the outermost shell of the nanowires. The magnetic moment per TM atom of TM/CNT system increases with increasing CNT diameter or decreasing nanowire thickness. Both the density of states and spin charge density analysis show that the spin polarization and the magnetic moments of all hybrid systems mainly originate from the TM nanowires, implying these systems can be applied in magnetic data storage devices.     

First principle study of the electronic and magnetic properties of a single iron atomic chain encapsulated in boron nitrite nanotubes

The electronic and magnetic properties for a single Fe atom chain wrapped in armchair (n,n) boron nitride nanotubes (BNNTs) (4≤n≤6) are investigated through the density functional theory. By increasing the nanotube diameter, the magnetic moments, total magnetic moments and spin polarization of systems are increased. We have calculated the majority and minority density of states (DOS) of armchair BNNT. Our results show that the magnetic moment of the system come mostly from the Fe atom chain. The magnetic moment on an Fe atom, the total magnetic moment and spin polarization decrease by increasing the axial separation of the Fe atom chain for the system. The BNNT can be used in the magnetic nanodevices because of higher magnetic moment and spin polarization.     

Mag netic properties of $$\hbox{Ni}_{13- n}\hbox{Al}_ n$$ clusters with n = 0–13

We report the magnetic properties of small Ni_13-nAl_n\hbox{Ni}_{13-n}\hbox{Al}_n clusters with n = 0–13 calculated in the framework of density functional theory. The cluster magnetic moment decreases with the sequential substitution of Ni by Al atoms, which can be attributed to a greater degree of hybridization that forces the pairing of the electrons in the molecular orbitals of Ni and Al. For Ni₇Al₆, the complete quenching of the cluster magnetic moment appears to be due to the antiferromagnetic alignment of atomic spins as revealed by the spin density plots.     

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.     

Structures,energetics and magnetic properties of (NiSn)<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> clusters with <Emphasis Type="Italic">n</Emphasis> = 1–6

We report the results of calculations which were performed to investigate equilibrium structures, electronic and magnetic properties of stoichiometric (NiSn) _n clusters with n = 1–6 within the framework of density functional theory. The calculated results show that the structural arrangement of (NiSn) _n clusters is dominated by the Ni-Sn and Ni-Ni interactions. We find that these binary clusters show significant variation in the geometries as compared to that of the host nickel clusters. The preference for tetrahedron unit of Ni₃Sn is seen in the lowest-energy configuration of these clusters. The multi-centre bonding between Ni atoms play an important role in stabilizing the stoichiometric Ni-Sn clusters. Doping of Sn atoms enhances the binding energy and reduces the ionization potential of nickel clusters. These binary clusters prefer the lowest spin state. For (NiSn)₆ the magnetic moment is 0 μB. The complete quenching of the cluster magnetic moment appears to be due to the antiferromagnetic alignment of atomic spins as revealed by the spin density plots.     

Structural, curvature and electronic properties of Rh adsorption on armchair single-walled carbon nanotube

This paper systematically studies the rolling effects of the (n, n) single-wall carbon nanotubes (SWCNT) with different curvatures on Rh adsorption behaviours by using density functional theory. The outside charge densities of SWCNTs are found to be higher than those inside, and the differences decrease with the increase of the tube radius. This electronic property led to the discovery that the outside adsorption energies are higher than the inside ones, and that the differences are reduced with the increase of the tube radius. Partial density of states and charge density difference indicate that these strong interactions induce electron transfer between Rh atoms and SWCNTs.     

First principles studies on the electronic structures of LiMxFe1-xPO4 （M = Co, Ni and Rh）

The local crystal structures and electronic structures of LiMxFe1-xPO4 （M = Co, Ni, Rh） are studied through first-principles calculations. The lattice constants and unit cell volumes are smaller for the Co and Ni doped materials than for pure LiFePO4, while larger than for the Rh doped material. The local structures around M atoms in the doped materials are studied in details. The total density of states （DOS） and atomic projected DOS （PDOS） are all calculated and analysed in detail. The results give a reasonable prediction to the improvement of electronic conductivity through Fe-site doping in LiFePO4 material.     

A quantum explanation of the magnetic properties of Mn-doped graphene

Mn-doped graphene is investigated using first-principles calculations based on the density functional theory(DFT).The magnetic moment is calculated for systems of various sizes,and the atomic populations and the density of states(DOS)are analyzed in detail.It is found that Mn doped graphene-based diluted magnetic semiconductors(DMS)have strong ferromagnetic properties,the impurity concentration influences the value of the magnetic moment,and the magnetic moment of the 8×8 supercell is greatest for a single impurity.The graphene containing two Mn atoms together is more stable in the 7×7 supercell.The analysis of the total DOS and partial density of states(PDOS)indicates that the magnetic properties of doped graphene originate from the p–d exchange,and the magnetism is given a simple quantum explanation using the Ruderman–Kittel–Kasuya–Yosida(RKKY)exchange theory.