笼状Au$lt;sub$gt;20$lt;/sub$gt;内掺$lt;i$gt;M$lt;/i$gt;$lt;sub$gt;13$lt;/sub$gt;($lt;i$gt;M$lt;/i$gt;=Fe，Ti)团簇磁性的密度泛函计算研究

采用密度泛函理论中的广义梯度近似方法,对M₁₃（M=Fe,Ti）以及M₁₃内掺Au₂₀团簇的几何结构和磁性进行了计算研究.结果表明：M₁₃和M₁₃内掺Au₂₀团簇的几何结构在0.006—0.05 nm误差范围内保持着I_h对称性.Fe₁₃团簇最低能态的总磁矩为44 μ_B,内掺到Au₂₀笼中后形成的Fe₁₃内掺Au₂₀团簇的最低能态总磁矩为38 μ_B,且Au原子与内掺Fe₁₃团簇之间存在着弱铁磁相互作用.Ti₁₃团簇在总磁矩为6 μ_B时能量最低,掺入Au₂₀笼后形成的Ti₁₃内掺Au₂₀团簇最低能态总磁矩是4 μ_B,内表面12个Ti原子与表面Au壳之间是弱铁磁相互作用,而与中心Ti原子之间是弱反铁磁相互作用.由于Au₂₀笼状外壳的影响,Fe₁₃内掺Au₂₀和Ti₁₃内掺Au₂₀团簇中Fe₁₃和Ti₁₃的磁矩比无金壳的Fe₁₃和Ti₁₃团簇的磁矩分别减少了6.81 μ_B和2.88 μ_B. 关键词： 几何结构 磁性 密度泛函理论     

MPb10(M=Ti,V,Cr,Cu,Pd)几何结构和磁性的密度泛函计算研究

采用密度泛函理论(density functional theory,DFT)中的广义梯度近似(generalized gradient approximation,GGA)对MPb10(M=Ti,V,Cr,Cu,Pd)四种同分异构体的几何结构和磁性进行了计算研究.发现在四种同分异构体中,D4d结构的MPb10(M=Ti,V,Cr,Cu,Pd)具有最大的结合能和能隙,表明D4d结构为其基态几何结构, 具有较高的化学稳定性.磁性计算显示:基态TiPb10团簇的磁矩为2 μB,Ti原子与周围的Pb原子之间存在着弱的铁磁相互作用.基态VPb10团簇的总磁矩为1 μB,V原子与周围的Pb原子之间既存在着弱的铁磁相互作用又存在弱的反铁磁相互作用.基态CuPb10团簇的磁矩为1 μB,Cu原子与周围的Pb原子之间存在着弱的铁磁相互作用.基态CrPb10 和PdPb10团簇的磁矩为零,体现为非磁性.由此可见,可以通过内掺不同过渡金属对Pb10团簇的化学反应活性和磁性进行调制.     

MAl_(12)(M=Ni、Mn)及其阴离子团簇的几何结构和磁性的计算研究

采用密度泛函理论(density functional theory,DFT)中的广义梯度近似(generalized gradient approximation,GGA)分别对Al_(13)和MAl_(12)(M=Ni、Mn)四种初始结构的中性和一价阴离子团簇进行计算研究.发现中性和阴离子团簇的基态几何结构均保持I_h对称性,并且基态阴离子团簇还具有较高的运动学稳定性.电磁性质计算显示:基态的中性和阴离子NiAl_(12)团簇分别带有2_(μB)、3_(μB)的磁矩,Ni原子的磁性几乎完全淬灭;而MnAl_(12)团簇分别带有7_(μB)、6_(μB)的磁矩,Mn原子的磁矩主要由3d轨道提供.基态团簇的表面原子出现了自旋分裂,与中心原子呈现出铁磁性作用.对垂直电离能和垂直亲和能的分析表明:中心原子被替代之后,团簇的得电子能力和失电子能力都有所降低.     

AunLa(n=1-8)团簇的密度泛函研究

采用密度泛函理论（DFT）中的杂化密度泛函B3LYP方法,在LANL2DZ基组水平上研究了AunLa (n=1-8)团簇的几何结构。计算并讨论了基态结构稳定性及电子性质。结果表明,当n=3-8时,基态结构均为三维结构且La原子趋向与更多的Au原子结合。团簇二阶能量差分,能隙和化学硬度计算结果显示除了AuLa外,具有偶数数目的团簇比奇数数目的团簇具有更好的稳定性,其中,Au3La团簇的稳定性相对较好。     

双金属掺杂M2@Si20(M=Ti, Zr, Hf)团簇结构和性质的理论研究

采用密度泛函理论(DFT)和相对论有效原子核势近似(RECP),对M2@Si20(M=Ti,Zr,Hf)团簇的几何结构和电子结构性质进行研究,发现内嵌的金属二聚体和十二面体硅笼构成了稳定的富勒烯结构。通过对团簇电子结构的分析,结果表明Si20团簇掺杂双金属后稳定性得到了提高。对团簇的电荷布局分析表明过渡金属原子(Ti, Zr, Hf)和硅笼之间发生了电荷反转。     

Fe、Co、Ni混合团簇磁性的密度泛函研究

基于13原子二十面体结构,采用密度泛函方法系统计算研究了Fe、Co及Ni单质及二元混合团簇的磁性.发现有限温度下团簇磁性随结构畸变的敏感性随Fe、Co、Ni顺序逐渐减弱,同时发现二十面体结构Fe_(13)及Co_(13)均具有不同磁矩的近简并低能态.对FeNi及CoNi混合团簇、其磁矩随组分的变化不存在反常现象,但对于FeCo混合团簇、其磁矩随组分的演化行为存在个别反常现象.我们认为:这种反常现象能够对FeCo非晶合金中的实验观测结果提供一种可能的理论解释.     

Ge_nMn(n≤8)团簇的电子结构与磁性的密度泛函理论研究

采用密度泛函理论下广义梯度近似方法,对Mn掺杂Ge基半导体团簇Ge_nMn(n≤8)的结构与磁性进行了理论研究.结果表明:Ge_nMn(n≤8)的最稳定构型与相应的Ge_(n+1)团簇相似.Mn掺杂后团簇的原子平均结合能与纯锗团簇比较近似;能量二次差分表明:Ge_3Mn和Ge_5Mn团簇较相邻团簇表现出较高的稳定性;当n=1,3和6时,HMO-LUMO能隙较大,n=2时,能隙较小,说明GeMn、Ge_3Mn和Ge_6Mn具有相对较好的化学稳定性,而Ge_2Mn具有较高的化学活性.对Ge_nMn(n≤8)团簇的磁性研究发现,除Ge_8Mn的总磁矩为1μB外,其他团簇的总磁矩均为3μB,且团簇的磁性主要来源于Mn原子.     

密度泛函理论计算Ga_nZn(n=1～7)团簇的几何结构和稳定性

采用密度泛函理论(Density Functional Theory,简称:DFT)中的广义梯度近似(Generalized Gradient Approximation,简称:GGA)中的B3LYP方法,选择LANL2DZ基组,对GanZn(n=1~7)小团簇的各种可能结构进行了优化,得到了每一种团簇的基态平衡结构.对每一种团簇中最稳定的团簇计算了平均键能、二阶差分能和分裂能,计算结果表明,Zn掺杂到Ga团簇中,稳定性出现奇偶交替的现象,当Ga原子为偶数时,团簇表现出较稳定的状态,当Ga原子为奇数时,团簇表现出不稳定的状态.与Gan纯团簇的比较发现Zn掺杂到Ga团簇时提高了其化学活性.     

混合团簇Cu11Fe2的的密度泛函研究

以Cu13非紧致低对称性基态结构及四种13原子高对称性（Ih、Oh、D5h、D3h）密堆积结构为初始构型，通过不等价位原子替换，利用密度泛函理论系统研究了Cu11Fe2混合团簇的稳定性及磁性．结果表明：对四种高对称性结构相应中心位替代构型稳定性均高于双表面位替代构型；Cu11Fe2团簇的基态结构为含一个中心位替代和一个表面位替代的Ih替换结构，这与Cu13的基态结构完全不同；Cu11Fe2无明显近基态同分异构现象；相较Cu13团簇、Cu11Fe2团簇的稳定性及磁性均得到增强．     

密度泛函理论计算GanZn(n=1-7)团簇的几何结构和稳定性

采用密度泛函理论(Density Functional Theory，简称：DFT)中的广义梯度近似(Generalized Gradient Approximation，简称：GGA)中的B3LYP方法，选择LANL2DZ基组，对GanZn(n=1-7)小团簇的各种可能结构进行了优化，得到了每一种团簇的基态平衡结构。对每一种团簇中最稳定的团簇计算了平均键能、二阶差分能和分裂能，计算结果表明，Zn惨杂到Ga团簇中，稳定性出现奇偶交替的现象，当Ga原子为偶数时，团簇表现出较稳定的状态，当Ga原子为奇数时，团簇表现出不稳定的状态。与对Gan纯团簇的比较发现Zn参杂到Ga团簇时提高了其化学活性。     

Au和3d过渡金属元素混合团簇结构、电子结构和磁性的研究

采用基于密度泛函理论的第一性原理方法系统研究了Au与3d过渡元素构成的混合小团簇的结构、稳定性、电子结构及磁性,得到了Au与3d过渡元素构成的混合小团簇的稳定结构.计算结果表明,Au与3d元素可形成大量的低能异构体,特别是有些异构体在结构上极相近,这不同于共价或离子键类型的团簇.与纯过渡金属团簇类似,这类团簇也表现出复杂的磁性.过渡金属元素的磁矩相比体材料而言既有增强的、也有减弱的,与轨道的交换劈裂密切相关.对于基态构型,AuCr₂,Au₂Cr_{2关键词： 密度泛函理论 第一性原理方法 团簇 电子结构}     

Magnetic properties in transition-metal-doped gold clusters: M@Au6 (M = Ti, V, Cr)

The electronic structure and magnetic properties in a series of transition-metal-doped Au clusters, MAu6- (M = Ti, V, Cr), are investigated experimentally using photoelectron spectroscopy (PES) and density functional calculations. PES features due to the impurity atoms and the host are clearly observed. It is found that all the MAu6- and MAu6 clusters possess a planar structure, in which the transition metal atom is located in the center of an Au6 ring and carries large magnetic moments (2, 3, and 4 muB for MAu6, M = Ti, V, and Cr, respectively).     

密度泛函方法研究NiSin(n=1~13)团簇

基于第一性原理,利用密度泛函理论中的广义梯度近似(GGA)系统研究了NiSin(n=1～13)团簇,在充分考虑自旋多重度的基础上讨论了这些团簇的生长行为,电子性质及其磁性,结果表明:NiSin 1的基态结构是在NiSin的基态结构上带帽一个Si原子而得到;随着团簇尺寸的增大,Ni原子逐渐从吸附在sin团簇的表面位置移动到Sin团簇笼内;掺杂Ni原子提高了硅团簇的稳定性;NiSi10团簇的稳定性在所有团簇中是最高的;电子总是从si向Ni转移,Ni原子所带的电荷数不仅与Ni原子的配位数有关,还与Nisin团簇的基态结构密切相关;n=1～2时,团簇的自旋总磁矩为2 μB,当n≥3时,团簇的磁性消失,这可能与Ni原子内部较强的sp-d杂化以及si原子内部的s-p杂化有关.     

Magnetism of Fe clusters embedded in Cu,Ag, and Au fcc matrices: density functional calculations

We present extensive first principles density functional theory (DFT) calculations dedicated to analyze the magnetic properties of small Fe _n clusters (n = 2,3) embedded in Cu fcc, Ag fcc and Au fcc matrices. We consider several dimers and trimers having different interatomic distances. In all cases the Fe atoms are embedded as substitutional impurities in the metallic network. For the case of the Fe dimers we have considered two magnetic configurations: ferromagnetic (antiferromagnetic), when the atomic magnetic moment of the Fe atoms are parallel (antiparallel) each other. For the case of dimers immersed in Cu and Ag matrices, the ground state corresponds to the ferromagnetic Fe dimer whose interatomic distance is a/√2. For Fe dimer immersed in the Au matrix the ground state corresponds to a ferromagnetic coupling when the interatomic distance is a√(3/2). In the case of the Fe trimers we have considered three or four magnetic configurations, depending on the Fe cluster geometry. For the case of Fe trimer immersed in Cu and Ag matrices we have found that the ground state corresponds to the ferromagnetic trimer forming an equilateral triangle with an interatomic distance equal to a/√2. The ground state for the Fe trimer immersed in the Au matrix corresponds to the ferromagnetic Fe trimer forming a right angle triangle.     

Theoretical study of the coadsorption of CO and O2 on doped cationic gold clusters MAun + (M = Ti, Fe, Au; n = 1, 6, 7)

We present a study based on first-principles calculations of the adsorption of CO on selected equilibrium configurations of MAu_nO₂ ⁺ (M = Ti, Fe; n = 1, 6, 7) complexes resulting from the adsorption of O₂ on doped cationic gold clusters MAu_n ⁺. Empirical rules for the formation of CO₂-MAu_nO⁺ complexes are outlined. The desorption energy of CO₂ is calculated. The adsorption of a second CO molecule on the residual MAu_nO⁺ complex leads in some cases to the formation of CO₂-MAu_n ⁺. The desorption of a second CO₂ molecule brings back to the initial doped gold cluster MAu_n ⁺.     

Electronic structure and magnetism of R(Fe,Si)12 (R = Y, Nd)

The newly developed full-potential linearized augmented plane wave (LAPW) and local orbitals (lo) based on standard APW methods are briefly introduced, and the structure and magnetic properties of R(Fe, Si)12 compounds (R = Y, Nd) are calculated using the method. The distribution of Si at different sites is analyzed based on total energy of one crystal unit with structure having been optimized. The characters of magnetic moments, total density of states (TDOS) and partial density of states (PDOS) for different crystal sites Si occupies are obtained and analyzed. The results show that the total magnetic moments of RFe10Si2 (R = Y, Nd) are larger than those of RFe10M2 (M = Ti, V, Cr, Mn, Mo and W) and the hybridization mechanism is seen as follows. Si(8j) reduce the magnetic moments of Fe at three sites, however, Si(8f) mainly reduce the magnetic moments of Fe(8i) and Fe(8j) atoms. The Curie temperature is markedly enhanced by the introduction of Si atoms according to spin fluctuation of DOS at Fermi level.     

Mössbauer spectroscopy studies of Dy(Fe,M)12 (M=Si,V,Ti) alloys

The⁵⁷Fe Mössbauer spectra have shown that the hyperfine field of DyFe₁₀Si₂ alloy and its quadrupole splitting at the 8i sites change steeply at 210 K, which are attributed to the spin reorientation transition. The stabilizing elements for the formation of the ThMn₁₂-structure can affect on the spin reorientation transition temperature. The differences of spin reorientation transition temperature of DyFe₁₀Si₂, DyFe₁₀V₂ and DyFe₁₁Ti alloys had been discussed. The quadrupole splitting at 8i sites of DyFe₁₀Si₂ alloy changes its sign at 210 K.     

Structural and magnetic properties of Ti12M clusters (M=Sc to Zn)

The geometries, electronic, and magnetic properties of the 3d atom doped icosahedron (ICO) Ti₁₂M (M=Sc to Zn), where a dopant atom replaces either the centra l(Ti₁₂M^c) or surface (Ti₁₂M^s) Ti atom in ICO Ti₁₃ cluster, have been systematically investigated by using the density functional theory. The structures of all the optimized Ti₁₂M^c and Ti₁₂M^s clusters are distorted ICO. Sc, Ni, Cu, and Zn atoms prefer to displace surface Ti atom, V, Cr, Mn, and Fe atoms prefer to displace central Ti atom. The position of impurity atom depends on the strength of the interaction between the central atom and the surface atoms. As compared to the pure Ti₁₃ cluster, Ti₁₂M^c and Ti₁₂M^s (M=V, Fe, Co, and Ni) clusters are more stable, Ti₁₂M^c and Ti₁₂M^s (M=Sc, Cr, Mn, Cu, and Zn) are less stable. Both Ti₁₂Ni^s and Ti₁₂Ni^c are magic clusters, which originate from their electronic as well as geometric closed shells. Because the exchange interaction prevails over the crystal field in Ti₁₂M clusters, the valence electrons fill molecular orbitals in terms of Hund’s rule of maximum spin.     

The relativistic density functional investigations on geometries, electronic and magnetic properties of Irn (n=1-13) clusters

<正>The Ir_n(n=1-13) clusters are studied using the relativistic density functional method with generalized gradient approximation.A series of low-lying structures with different spin multiplicities have been considered.It is found that all the lowest-energy Ir_n(n=4-13) geometries prefer non-compact structures rather than compact structure growth pattern.And the cube structure is a very stable cell for the lowest-energy Ir_n(n8) clusters.The second-order difference of energy,the vertical ionization potentials,the electron affinities and the atomic average magnetic moments for the lowest-energy Ir_n geometries all show odd-even alternative behaviours.     

Two-dimensional MTe2 (M = Co,Fe, Mn,Sc, Ti) transition metal tellurides as sodium ion battery anode materials: Density functional theory calculations

We performed density functional theory calculations to probe sodium adsorption and diffusion properties on two-dimensional (2D) MTe₂ (M = Co, Fe, Mn, Sc, Ti) first-row transition metal tellurides, and gauge their potentials as anode materials for sodium-ion batteries (NIBs). In this work, we found that all considered MTe₂ possess strong sodium adsorption properties and excellent diffusion kinetics. Moreover, sodium atoms prefer to bind on sites that are farther apart rather than on nearby sites, implying that (1) the sodium clustering is not favored and (2) the large adsorption energies are essentially due to the sodium-MTe₂ interaction. We further adopted ab initio random structure search to compute probable stable sodium adsorption configurations, to obtain more accurate capacities and open circuit voltages. The calculated capacities and open circuit voltage are reasonable, and are suitable for anode applications. Our results show that in general, 2D MTe₂ sheets have suitable sodium adsorption energies and diffusion barriers, and could be applied as sodium ion battery anode materials.