ConAl (n= 1–8)合金团簇结构和磁性质研究

采用密度泛函理论中的广义梯度近似(DFT-GGA)对Co_nAl (n= 1–8)合金团簇进行了系统的几何、 电子结构和磁性质研究. 研究结果表明Al原子倾向于与Co原子形成最大的成键数, 即Al原子均处在团簇原子拥有最大配位数的位置上. Al掺杂后Co_nAl团簇的稳定性减弱, 磁性降低. 磁性降低的幅度与实验上对较大Co_nAl_M团簇的磁性检测结果获得了很好地符合. 在所有Co_nAl团簇的最稳定结构中, 除Co₄Al外, Al与近邻Co原子均呈现反铁磁性耦合. 相对于纯Co团簇,非磁性Al元素的掺入以及Al掺杂后Co原子整体自旋极化的减弱 是导致Co_nAl团簇磁性的降低主要原因. 关键词： nAl合金团簇')" href="#">Co_nAl合金团簇 几何结构 磁性 自旋极化     

Geometries, stabilities and electronic properties of small Nb-doped gallium clusters: A density functional theory study

The host Ga_n+1 and doped Ga_nNb (n=1-9) clusters with several spin configurations have been systematically investigated by a relativistic density functional theory (DFT) with the generalized gradient approximation. The optimized equilibrium geometries tend to prefer the close-packed configurations for small Nb-doped gallium clusters up to n=9. The average binding energies per atom (E_b/atom), second-order differences of total energies (Δ₂E), fragmentation energies (E_f) and HOMO-LUMO gaps of Ga_n+1 and Ga_nNb (n=1-9) clusters are studied. The results indicate the doping of Nb atom in gallium clusters improves the chemical activities. In particular, the clusters with sizes of Ga₄Nb and Ga₇Nb are found to be more stable with respect to their respective neighbors. Our calculated vertical ionization potentials (VIPs) exhibit an obvious oscillating behavior with the cluster size increasing, except for Ga₃ and Ga₄Nb, suggesting the Ga₃, Ga₅, Ga₇, GaNb, Ga₃Nb, Ga₆Nb and Ga₈Nb clusters corresponding to the high VIPs. In the case of vertical electron affinities (VEAs) and chemical hardness η, VEAs are slightly increasing whereas chemical hardness η decreasing as Ga_nNb cluster size increases. Besides, the doping of Nb atom also brings the decrease as the cluster sizes increases for atomic spin magnetic moments (μ_b).     

Structures, stabilities and electronic properties of FePbn (n=1-14) clusters: Density-functional theory investigations

The structures, stabilities and electronic properties of FePb_n (n=1-14) clusters have been studied using the density-functional theory (DFT). Extensive search of the ground-state structures has been carried out by considering a larger number of structural isomers for each cluster size. The Fe atom gradually falls into the interior of the Pb framework as the number of Pb atom increases from 1 to 14. The FePb_n clusters at n=3, 5, 10, 12 have relatively higher stability by analyzing the averaged binding energy and the second-order energy difference. Especially, FePb₁₂ is more stable, owing to its highest symmetrical icosahedron structure. The magnetic moments of FePb_n clusters do not quench when Fe atom is encapsulated in the Pb framework and mostly originate from 3d state of Fe atom.     

Pt_nAl(n=1—8)小团簇的密度泛函理论研究

采用密度泛函理论方法,在BPW91/LANL2DZ水平下详细研究了Pt n Al(n=1—8)团簇的几何结构、稳定性和电子性质.同时,分析了团簇的结构演化规律、平均结合能、二阶能量差分、能隙、磁性、Mulliken电荷和电极化率.结果表明:除Pt2Al外,所有Pt n Al(n=1—8)团簇的基态几何结构都可以用Al原子替换Pt n+1基态构型中的Pt原子得到,且Al原子位于较高的配位点上.二阶能量差分、能隙的分析结果表明,PtAl和Pt4Al团簇相对其他团簇具有较高的稳定性.Mulliken电荷分析表明,Al原子所带的电荷转移到Pt原子上,Al原子是电荷的捐赠者.磁性的分析说明,单个Al原子的加入对Pt n团簇的平均每原子磁矩随尺寸的变化趋势没有影响,但总体上降低了Pt n团簇的平均磁矩.极化率的研究表明,富Pt团簇的非线形光学效应强,容易被外场极化.     

密度泛函理论研究ZrnCo(n=1—13)团簇的结构和磁性

利用密度泛函理论中的广义梯度近似对Zr_nCo(n=1—13)团簇进行了结构优化、能量和频率的计算,研究了Zr_nCo团簇的平衡几何结构、稳定性、电子性质和磁性.结果表明：Zr₄Co,Zr₇Co,Zr₉Co和Zr₁₂Co团簇的基态稳定性较高,是幻数团簇,尤其是Zr₁₂Co团簇基态为I_{h< 关键词： n}Co团簇')" href="#">Zr_nCo团簇 平衡几何结构 稳定性和磁性     

WnNim(n+m=8)团簇结构与电子性质的理论研究

采用密度泛函理论(DFT)中的B3LYP方法,在Lanl2dz基组水平上对W_nNi_m(n+m=8)团簇的各种可能构型进行了几何参数全优化,得到了它们的基态构型;并对基态构型的平均结合能、Wiberg键级(WBI)、磁学性质、NBO进行了分析,结果表明:团簇随着W原子数的增多,稳定性增强,n≥5时,结构中都含有纯钨团簇的结构基元;W-W键级高于W-Ni键和Ni-Ni键;W₅Ni₃,W₆Ni₂团簇发生了"磁矩猝灭"的现象;在W,Ni原子内部,轨道电荷发生了转移,产生了"轨道杂化"现象,W,Ni原子之间也发生了电荷转移形成了较强的化学键. 关键词： nNi_m(n+m=8)团簇')" href="#">W_nNi_m(n+m=8)团簇 几何结构 电子性质 密度泛函理论     

Geometrical, electronic, and magnetic properties of small AunSc (n=1-8) clusters

Geometrical, electronic, and magnetic properties of the Sc-doped gold clusters, Au_nSc (n=1-8), have been studied using the density-functional theory within the generalized gradient approximation. An extensive structural search shows that the Sc atom in low-energy Au_nSc isomers tends to occupy the most highly coordinated position. The substitution of a Sc atom for an Au atom in the Au_n+1 cluster markedly changes the structure of the host cluster. Moreover, we confirm that the ground-state Au₆Sc cluster has a distortion to a lower D_2h symmetry. The relative stabilities and electronic properties of the lowest-energy Au_nSc clusters are analyzed based on the averaged binding energies, second-order energy differences, fragmentation energies, chemical hardnesses, and HOMO-LUMO gaps. It is found that the magic Au₃Sc cluster can be perceived as a superatom with high chemical stability and its HOMO-LUMO gap is larger than that of the closed-shell Zr@Au₁₄ cluster. The high symmetry and spin multiplicity of the Au₃Sc and Au₆Sc clusters are responsible for their large vertical ionization potential and electron affinity. The magnetism calculations indicate that the magnetic moment of the Sc atom in the ground-state Au_nSc (n=2-8) clusters gradually decreases for even n and is completely quenched for odd n.     

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     

密度泛函理论计算GenFe(n=1—8)团簇的基态结构及其磁性

基于第一性原理，利用密度泛函理论中的广义梯度近似 (GGA)对Ge_nFe(n=1—8)团簇进行了结构优化、能量及频率的计算，得到了 Ge_nFe(n=1—8)团簇在不同自旋多重度下的平衡构型及其基态结构.结果表明：Ge_nFe混合团簇的平均结合能明显比相应纯锗团簇的平均结合能有所增大，即掺杂Fe原子可以提高锗团簇的稳定性；纯锗团簇的基态除了Ge₂为自旋三重态外其他均为单重态，而混合团簇Ge_nFe(n=1—8)的基态均为自旋三重态；对Ge_nFe(n=1—8)团簇的磁性做了较系统的研究，发现团簇总磁矩随团簇尺寸增大基本稳定在2μ_B (只有Ge₈Fe的总磁矩2.391μ_B较明显地偏离了2μ_B)，另外团簇中Fe原子的磁矩在2.5μ_B左右振荡. 关键词： nFe团簇')" href="#">Ge_nFe团簇 密度泛函理论(DFT) 自旋多重度 磁矩     

Geometries,stabilities, electronic and magnetic properties of small PdnIr (n = 1–8) clusters from first-principles calculations

The geometrical structures, relative stabilities, electronic and magnetic properties of small Pd_nIr (n = 1–8) clusters have been systematically investigated using density functional theory at the B3PW91 level. The optimised geometries show that the lowest-energy structures of Pd_nIr clusters prefer a three-dimensional configuration. The relative stability of these clusters was examined by analysis of the binding energies per atom, fragmentation energies, the second-order difference of energies and the HOMO–LUMO energy gaps as a function of cluster size. The obtained results exhibit that the Pd₂Ir, Pd₃Ir and Pd₅Ir clusters are more stable than their neighbouring clusters. The energy gap of the Pd₂Ir cluster is the largest of all the clusters (2.258 eV). In addition, the charge transfers, vertical ionisation potentials, vertical electron affinities and chemical hardness were calculated and discussed. The magnetism calculations indicate that the total magnetic moment of Pd_nIr clusters is mainly localised on the iridium atom for Pd_1–6Ir clusters. Meanwhile, the 5d orbital plays the key role in the magnetic moment of the iridium atom.     

Geometries, stabilities, and electronic properties of gold-magnesium (AunMg) bimetallic clusters

The geometrical structures, relative stabilities, and electronic properties of bimetallic Au_nMg (n=1-8) clusters have been systematically investigated by means of first-principle density functional theory. The results show that the ground-state isomers have planar structures for n=1-7. Here, the calculated fragmentation energies, the second-order difference of energies, the highest occupied-lowest unoccupied molecular orbital energy gaps, and the hardness exhibit a pronounced odd-even alternation, manifesting that the clusters, especially Au₂Mg, with even-number gold atoms have a higher relative stability. On the basis of natural population analysis, the charge transfer and magnetic moment are also discussed.     

Density functional theory study of AunMn(n=1-8) clusters

Equilibrium geometries, relative stabilities, and magnetic properties of small Au_nMn (n=1-8) clusters have been investigated using density functional theory at the PW91P86 level. It is found that Mn atoms in the ground state Au_nMn isomers tend to occupy the most highly coordinated position and the lowest energy structure of Au_nMn clusters with even n is similar to that of pure Au_n+1 clusters, except for n=2. The substitution of Au atom in Au_n+1 cluster by a Mn atom improves the stability of the host clusters. Maximum peaks are observed for Au_nMn clusters at n=2, 4 on the size dependence of second-order energy differences and fragmentation energies, implying that the two clusters possess relatively higher stability. The HOMO-LUMO energy gaps of the ground state Au_nMn clusters show a pronounced odd-even oscillation with the number of Au atoms, and the energy gap of Au₂Mn cluster is the biggest among all the clusters. The magnetism calculations indicate that the total magnetic moment of Au_nMn cluster, which has a very large magnetic moment in comparison to the pure Au_n+1 cluster, is mainly localized on Mn atom.     

密度泛函理论对CoBen(n=1—12)团簇结构和性质的研究

采用密度泛函理论中的广义梯度近似(GGA)对CoBe_n(n=1—12)团簇的几何构型进行优化，并对能量、频率和磁性进行了计算，同时考虑了电子的自旋多重度.得到了CoBe_n(n=1—12)团簇最低能量结构的自旋多重度是2和4.在CoBe_n(n=1—12)团簇中，Co原子的磁矩出现了奇偶振荡，当n=6时，Co原子的4s，3d和Be原子的2s，2p较强杂化、Co-Be键长的减小以及对称性的降低导致Co原子的磁矩最小.通过对CoBe_n(n=1—12)团簇电子性质的分析，得出了掺杂可以增强团簇稳定性和有利于增加合金化学活性的结论.n=5，10是团簇的幻数. 关键词： n团簇')" href="#">CoBe_n团簇 自旋多重度 磁矩 电子性质     

Structures, stabilities and magnetic properties of FeCon−1 (n≤16) clusters

Under GGA, size dependence of the geometrical structures, stabilities and magnetic properties of FeCo_n−1 clusters (n≤16) have been investigated together with the Co_n clusters for comparison using DFT within the PAW method implemented in VASP. The replaced Fe atom is favorable to occupy the surface position except for FeCo₁₃. The peaks appeared at n=6, 9 and 11 for FeCo_n−1 clusters and at n=6, 9 and 12 for Co_n clusters on the size dependence of second difference of total energy imply that these clusters possess relatively higher stability. The magnetic moment is strongly correlated with the effective hybridization, which is closely related to the average bond length 〈d〉 and average coordination number 〈n_c〉. A small change in the total charge of Fe atom in FeCo_n−1 clusters will lead to a relative large reverse change in the total magnetic moment of Fe atom.     

Structure and magnetic properties of La-doped Si<Subscript>n</Subscript> (n = 1–12, 24) clusters: a density functional theory investigation

In the framework of density functional theory (DFT), the structure and magnetic properties of La-doped Si_n clusters have been systematically studied. It is found that La atom always prefers locating on the surface site of the clusters and no cage-like structures are found up to n = 12. The La atom doping remarkably enhances the stabilities of silicon clusters. In contrast to some other clusters with the magnetic moment completely quenched, La doping is shown to invariable magnetism with the total spin magnetic moment of LaSi_n clusters 1 _¼B up to n = 24, as that of a free La atom.     

BenLa (n=1—18) 团簇的结构、电子性质和磁性

采用基于密度泛函理论的第一性原理方法,在多种初始构型下充分考虑自旋多重度,研究了Be_nLa团簇的平衡几何结构、电子性质和磁性.结果表明：Be_nLa团簇的基态附近有许多能量非常接近的同分异构体,说明该团簇结构较复杂,对其基态的寻找极具挑战性.Be_nLa团簇具有磁性且稳定性远高于Be_n+1团簇,由此可知通过选择合适的掺杂元素可能得到高稳定性的磁性团簇.Be_{1 关键词： n}La团簇')" href="#">Be_nLa团簇 平衡几何结构 电子性质和磁性     

密度泛函理论研究Run和RunAu(n=1-12)团簇的结构和电子性质

采用密度泛函理论中的广义梯度近似(GGA) 对 Ru_n Au和Ru_n 团簇的几何构型进行优化,并对能量、频率、电子性质和磁性质进行了计算. 结果表明,Ru_n Au团簇的最低能量结构可以通过Au原子代替Ru_n+1团簇中的Ru原子生长而成.除了局域的结构畸变,Ru_n Au和Ru_n+1团簇具有相似的几何结构.二阶能量差分、电离势、亲和势和分裂能表明Ru₅, Ru₈, Ru₅Au, Ru₈Au 是稳定的团簇,Au的掺杂没有改变Ru_n 的相对稳定性.通过电子性质的分析发现,当Au原子掺杂在Ru_n 中,团簇的化学活性增加,且团簇的能隙主要由电子的配对效应决定;对于大多数团簇来说,Au原子掺杂提高了Ru_n Au的磁矩. 关键词： n Au和Ru_n 团簇')" href="#">Ru_n Au和Ru_n 团簇 几何结构 电子性质     

A comparative study on geometries,stabilities, and electronic properties between bimetallic AgnX（X=Au,Cu;n=1-8）and pure silver clusters

Using the meta-generalized gradient approximation (meta-GGA) exchange correlation TPSS functional, the geo- metric structures, the relative stabilities, and the electronic properties of bimetallic Ag n X (X=Au, Cu; n=1–8) clusters are systematically investigated and compared with those of pure silver clusters. The optimized structures show that the transition point from preferentially planar to three-dimensional structure occurs at n = 6 for the Ag n Au clusters, and at n = 5 for Ag n Cu clusters. For different-sized Ag n X clusters, one X (X=Au or Cu) atom substituted Ag n+1 structure is a dominant growth pattern. The calculated fragmentation energies, second-order differences in energies, and the highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) energy gaps show interesting odd–even oscillation behaviours, indicating that Ag 2,4,6,8 and Ag 1,3,5,7 X (X=Au, Cu) clusters keep high stabilities in comparison with their neighbouring clusters. The natural population analysis reveals that the charges transfer from the Ag n host to the impurity atom except for the Ag 2 Cu cluster. Moreover, vertical ionization potential (VIP), vertical electronic affinity (VEA), and chemical hardness (η) are discussed and compared in depth. The same odd–even oscillations are found for the VIP and η of the Ag n X (X=Au, Cu; n=1–8) clusters.     

Thermal expansion and magnetostriction in Pr(n+2)(n+1)Nin(n−1)+2Sin(n+1) compounds

Thermal expansion and magnetostriction of members of a homologous series of compounds based on the alloy series Pr_(n+2)(n+1)Ni_n(n−1)+2Si_n(n+1) have been measured. The crystal structures of these compounds are closely interrelated because they form trigonal prismatic columns in which the number of trigonal prisms that form the base of the trigonal columns is determined by the value of n in the chemical formula. Two compositions were investigated, Pr₅Ni₂Si₃ and Pr₁₅Ni₇Si₁₀, corresponding to n=3$n=3$ and n=4,$n=4,$ respectively. The results were analyzed and used to determine the location of magnetic phase transitions by calculating the magnetic contribution to thermal expansion using the Gruneisen–Debye theory. This allowed more precise determination of the magnetic transition temperatures than could be achieved using the total thermal expansion. The results show two phase transitions in each material, one corresponding to the Curie temperature and the other at a lower temperature exhibiting characteristics of a spin reorientation transition.     

Structural, electronic and magnetic properties of Mn, Co, Ni in Gen for (n=1-13)

The structural, electronic and magnetic properties of TMGe_n (TM=Mn, Co, Ni; n=1-13) have been investigated using spin polarized density functional theory. The transition metal (TM) atom prefers to occupy surface positions for n<9 and endohedral positions for n≥9. The critical size of the cluster to form endohedral complexes is at n=9, 10 and 11 for Mn, Co and Ni respectively. The binding energy of TMGe_n clusters increases with increase in cluster size. The Ni doped Ge_n clusters have shown higher stability as compared to Mn and Co doped Ge_n clusters. The HOMO-LUMO gap for spin up and down electronic states of Ge_n clusters is found to change significantly on TM doping. The magnetic moment in TMGe_n is introduced due to the presence of TM. The magnetic moment is mainly localized at the TM site and neighbouring Ge atoms. The magnetic moment is quenched in NiGe_n clusters for all n except for n=2, 4 and 8.