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1.
We investigate magnetic and structural properties of iron clusters up to Fe 32, well extending into the size range accessible by experiment. A density-functional based tight-binding scheme fully incorporating the effects of spin polarisation and charge transfer in a self-consistent manner has been used. The potential hypersurfaces have been scanned by an unconstrained search using a genetic algorithm. Results for smaller clusters up to Fe 17 are validated against more sophisticated density functional theory calculations. Our magnetic moment data show a strong change around Fe 13 being unique in this size range. For the larger cluster sizes a smooth decrease of the clusters average spin magnetic moments is found in good agreement with experimental data. 相似文献
2.
We perform ab initio calculations to investigate Ni 13 clusters reaction under an oxygen atmosphere. We dynamically evaluate the effect on structural, electronic, and magnetic properties for pristine and oxidated clusters. As oxygen chemisorption increases, the pristine icosahedral cluster tends to adopt a cubic sodium chloride configuration, resistant to further oxidation. Although each chemisorbed O atom draws one electron, the cluster magnetization stays in the 4-8 μ B range, with magnetic moment localized at Ni atoms. Oxygen effect on the electronic structure is to hybridize O(p) − Ni(s, d) among low-lying occupied states and to induce a HOMO-LUMO gap opening, while also shifting downwards the electronic band edges, making them favorably aligned with photocatalytic reactions. 相似文献
3.
A systematic quantum chemical investigation on the geometric, energetic, electronic and magnetic properties of vanadium-copper nanoalloy clusters ( n = 1–12) is performed by using BPW91/LanL2DZ calculations. The calculated results show that the structural evolution of Cu n V clusters favors a compact and icosahedral growth pattern and V atom favors occupying the most highly coordinated position. Energetic properties show that doping of one V atom contributes to strengthening the stability of the copper clusters with the growth of the clusters. The stacking mode of clusters apparently has a more important effect on the clusters stability than the electronic structure. However, electronic structures have some contribution to the stability of Cu n V clusters as well. The electronic properties of Cu n V are analyzed through vertical ionization potential (VIP), vertical electron affinity (VEA) and chemical hardness (η). The magnetism calculations show that when doping V atom in copper clusters, the cluster system generate a very large magnetic moment and its contribution mainly comes from the 3 d orbital of doping-V atom. 相似文献
4.
The local magnetic property, d electronic structure and the charge transfer effect of Fe impurity in Al clusters have been studied by using a tight-binding model Hamiltonian in the unrestricted Hartree-Fock approximation, which includes intra-atomic and interatomic Coulomb interactions. We have obtained that local magnetic moment of Fe impurity in FeAl N clusters decreases with increasing cluster size and convergences to zero (that of bulk given by Anderson) with N larger than 12, meanwhile, the local magnetic moment for smaller clusters depends on the clusters size and it is a monotonous descent function of cluster size. We have also found that the spin splitting of the localized d states decreases as the cluster size increases, which mainly results from the interaction between the localized electrons of Fe atom and the delocalized electrons of Al atoms. 相似文献
5.
We present results for the magnetic properties of (Fe x Cr 1?x ) n alloy clusters obtained by using a tight-binding Hubbard Hamiltonian in the unrestricted Hartree-Fock approximation. The dependence of the average magnetic moment, local magnetic moments, magnetic order, and cohesive energy on the size and composition of the cluster were determined. In agreement with surface calculations, we find that the average magnetic moment of the alloy is larger than that of the cluster of one element. For n=15 a transition from ferromagnetic to antiferromagnetic order is obtained for x≈0.4?0.53. We discuss the importance of the overlap interaction in the spin polarized charge distribution of the alloy (e.g., charge transfer, local magnetic moments). The characteristic properties of the mixed clusters are also discussed by comparison with available results for homogeneous clusters. 相似文献
6.
The electronic structure and magnetism of 13 atom clusters of ruthenium, rhodium and palladium having face centered cubic(fcc) geometry has been studied using a Gaussian orbital basis and the local spin density approximation. Calculations were done for the lattice spacings relevant to the bulk crystal lattice. Using the fixed moment states as input potentials, as many as 3 self-consistent states were obtained for these clusters. The 3 converged states of Rh 13 cluster is found to have magnetic moments of 0.69 μB , 1.00 μB and 1.46 μB . Out of these states, 0.69 μB moment state is found to be the ground state. But the total energy difference between the 0.69 μB and 1.00 μB state is very small. The 1.46 μB moment state coincides with the state reported previously by other authors which was obtained using the discrete variational method. The experimentally observed moment was around 0.47 μB . Our calculated moment is closer to the experimentally observed moment than the previously reported moment, but is still a bit larger. Ru 13 cluster is also found to have large moments, and 3 self-consistent states are also obtained for this cluster. The 3 magnetic moments of the Ru 13 cluster are 0.46 μB , 0.62 μB and 1.08 μB . Out of these states, 0.62 μB moment state is found to be the ground state. For the Pd 13 cluster, in addition to the nonmagnetic state previously reported, a state with magnetic moment of 0.46 μB is also found to exist indicating possible magnetism in cluster phase. 相似文献
7.
A disk‐shaped [Fe III7(Cl)(MeOH) 6(μ 3‐O) 3(μ‐OMe) 6 (PhCO 2) 6]Cl 2 complex with C3 symmetry has been synthesised and characterised. The central tetrahedral Fe III is 0.733 Å above the almost co‐planar Fe III6 wheel, to which it is connected through three μ 3‐oxide bridges. For this iron‐oxo core, the magnetic susceptibility analysis proposed a Heisenberg–Dirac–van Vleck (HDvV) mechanism that leads to an intermediate spin ground state of S=7/2 or 9/2. Within either of these ground state manifolds it is reasonable to expect spin frustration effects. The 57Fe Mössbauer (MS) analysis verifies that the central Fe III ion easily aligns its magnetic moment antiparallel to the externally applied field direction, whereas the other six peripheral Fe III ions keep their moments almost perpendicular to the field at stronger fields. This unusual canted spin structure reflects spin frustration. The small linewidths in the magnetic Mössbauer spectra of polycrystalline samples clearly suggest an isotropic exchange mechanism for realisation of this peculiar spin topology. 相似文献
8.
The structural and magnetic properties of small gas-phase Fe m Co n clusters with m?+? n ranging between 2 and 7 atoms are investigated using spin-polarized density functional theory. For a given cluster size possible compositions are subject to optimization using a variety of initial structures. The geometry, bond lengths, binding energies and magnetization are reported for the lowest energy structures. The results show that a magnetization peak occurs for Fe 4, while for hybrid clusters, switching a cobalt atom with an iron atom increases the cluster’s total magnetization by 1?μ B . Our structural predictions are generally in agreement with other theoretical results; the origin of the discrepancies arising in some cases is discussed. 相似文献
9.
A 2-D framework composed of a chair-like {Fe 6} cluster and BTC linkers, [Fe 6(BTC) 2(HCOO) 6(DMF) 6] ( 1, BTC?=?1,3,5-benzenetricarboxylate), has been synthesized under solvothermal conditions and characterized by elemental analysis, infrared spectroscopy, thermal gravimetric analysis, and single-crystal X-ray diffraction analysis. The {Fe 6} cluster contains six iron ions and six formate ligands, with each formate coordinating with three iron ions to construct the hexa-nuclear iron wheel. The {Fe 6} wheels are further connected via BTC ligands resulting in the first example of a 2-D framework based on {Fe 6} clusters and BTC linkers. A magnetic study indicates that intramolecular antiferromagnetic interactions exist in the hexa-nuclear iron cluster. 相似文献
10.
In novel superatom chemistry, it is very attractive that all‐metal clusters can mimic the behaviors of nonmetal atoms and simple nonmetal molecules. Wizardly all‐metal halogen‐like superatom Al 13 with 2P 5 sub shell (corresponding to the 3p 5 of chlorine) is the most typical example. In contrast, how to mimic the behaviors of magnetic transition‐metal atom using all‐nonmetal cluster is an intriguing challenge for superatom chemistry. In response to this based on human intuition, using quantum chemistry methods and extending jellium model from metal cluster to all‐nonmetal cluster, we have found out that all‐nonmetal octahedral B 6 cluster with characteristic jellium electron configuration 1S 21P 62S 21D 8 in the triplet ground state can mimic the behaviors of transition‐metal Ni atom with electron configuration 3s 23p 64s 23d 8 in electronic configuration, physics and chemistry. Interestingly, the characteristic order of 1S1P2S1D for the B 6 nonmetal cluster with short B‐B lengths is different from that of the traditional jellium model—1S1P1D2S for metal clusters with long M‐M lengths, which exhibits a novel size effect of nonmetal cluster on jellium orbital ordering. Based on the jellium electron configuration, the B 6 with the spin moment value of 2μ B is a new all‐nonmetal transition‐metal nickel‐like superatom exhibiting a new kind of all‐nonmetal magnetic superatom. Finding the application of the all‐nonmetal magnetic superatom, we encapsulate the magnetic superatom B 6 inside fully hydrogenated fullerene forming a clathrate B 6@C 60H 60 with the spin moment value of 2μ B. As the C 60H 60 cage as a polymerization unit can conserve the spin moment of endohedral B 6, the clathrate B 6@C 60H 60 is a new all‐nonmetal magnetic superatom building block. Naturally, magnetic superatom structures of the B 6 and B 6@C 60H 60 may be metastable. 相似文献
11.
Magnetic properties of the lyonsite-type phase, Cu 3.9Fe 3.4V 6O 24, that has been synthesized by a standard solid-state reaction method, were investigated by dc magnetization and electron paramagnetic resonance (EPR) techniques. Complex magnetic behavior and transition to the antiferromagnetic phase at liquid helium temperature have been revealed by measurements of dc susceptibility in ZFC and FC modes in the 2–300 K temperature range as well as static magnetization in magnetic fields up to 70 kOe. Strong antiferromagnetic interactions in clusters or chains of magnetic ions even at high temperatures has been deduced from the obtained value of the effective magnetic moment that was significantly smaller than expected for nominal valences of iron and copper ions. The presence of antiferromagnetic iron dimers in the high-temperature range, critical slowing down of spin fluctuations on approaching Neel temperature and the existence of magnetically isolated iron ions in the antiferromagnetic phase has been suggested from the temperature dependence of EPR parameters (g-factor, linewidth, integrated intensity) obtained by fitting the experimental spectrum with Lorentzian lineshape. 相似文献
13.
The structural stability and electronic-structure of icosahedral La(13), La(-1) (13), and La(+1) (13) clusters have been studied by DMOL cluster method based on density-functional theory. The ground state of all-electron with relativity results is shown to be a distorted D(2h) icosahedron by the Jahn-Teller effect. However, the binding energies of D(3d) and D(5d) are very close to that of the D(2h) structure for La(13), La(-1) (13), and La(+1) (13) clusters. The effective core potential results show that the true ground state is D(5d) structure. The clusters have small magnetic moments and the symmetry of cluster is an important factor in determining the magnetic moments of the clusters. The effects of interatomic spacing and coordination on atomic magnetic moment are discussed. Further, 5d electrons dominate the hybrid orbitals below the Fermi level in the neutral cluster and contribute the main spin of clusters. 相似文献
14.
Due to its unique magnetic properties offered by the open-shell electronic structure of the central metal ion, and for being an effective catalyst in a wide variety of reactions, iron phthalocyanine has drawn significant interest from the scientific community. Nevertheless, upon surface deposition, the magnetic properties of the molecular layer can be significantly affected by the coupling occurring at the interface, and the more reactive the surface, the stronger is the impact on the spin state. Here, we show that on Cu(100), indeed, the strong hybridization between the Fe d-states of FePc and the sp-band of the copper substrate modifies the charge distribution in the molecule, significantly influencing the magnetic properties of the iron ion. The Fe II ion is stabilized in the low singlet spin state ( S=0), leading to the complete quenching of the molecule magnetic moment. By exploiting the FePc/Cu(100) interface, we demonstrate that NO 2 dissociation can be used to gradually change the magnetic properties of the iron ion, by trimming the gas dosage. For lower doses, the FePc film is decoupled from the copper substrate, restoring the gas phase triplet spin state ( S=1). A higher dose induces the transition from ferrous to ferric phthalocyanine, in its intermediate spin state, with enhanced magnetic moment due to the interaction with the atomic ligands. Remarkably, in this way, three different spin configurations have been observed within the same metalorganic/metal interface by exposing it to different doses of NO 2 at room temperature. 相似文献
15.
Electronic states of icosahedral Cu 13 and Cu 12 clusters were calculated by the DV-X α method which took into account of many-electron effects. The valence 3 d orbitals are localized within atom and isolated from the valence 4 s orbitals extended over the whole cluster. The characteristic feature of the states of s valence electrons of Cu 13 cluster well corresponds to that of one-electron picture i.e. the shell model of the 3-dimensional isotropic harmonic oscillator potential. Electronic states of valence levels of Cu 12 cluster which have no central atom fairly well correspond to those of a combined potential of the harmonic oscillator and a 3-dimensional Gaussian potential barrier at the center of the cluster. 相似文献
16.
用密度泛函方法对过渡金属Mn 5, Mn 6的各种可能构型, 在PW91/ZoraTZ2P水平上进行了理论研究. 计算结果表明: 构型是自旋变化、磁性的敏感因素, Mn 5最稳定构型为弱铁磁性的三角双锥体(磁矩为3, D3h). Mn 6的最稳定构型为铁磁性的畸变八面体(磁矩为16, C4v). 各种异构体虽然多重度不同, 但每个原子的自旋极化度均在3以上. 构型稳定与否取决于原子间的交换耦合作用, 而原子间的这种作用又与自旋极化度的方向、大小息息相关. 相似文献
17.
Metal superatomic nanoclusters, with electronic structures similar to those of one certain atom, are an important type of metal clusters. Interestingly, metal clusters with metal cores composed of either icosahedral M 13 or icosahedral assemblies always have a greater potential to become superatomic clusters. Furthermore, superatomic clusters with similar electronic compositions could possess various geometric structures, owing to differences in the shells; this provides a deeper understanding of the metal superatomic cluster and the assembly for nanomaterials. Therefore, this review focuses on the geometric and electronic structures of gold/silver superatomic clusters based on icosahedron M 13 units and their alloys, which will facilitate the development of various applications of superatomic clusters. 相似文献
18.
The structures, magnetic, and electronic properties of the ground-state (Fe2N)m (m?=?1–4) and (Fe3N)n (n?=?1–3) clusters have been investigated by using first-principles. The structure of the (Fe2N)m and (Fe3N)n clusters is a compromise that the N atoms approach more Fe atoms and the N atoms repel each other. The structural stabilities of the (Fe2N)m and (Fe3N)n clusters increase with the increasing of the N ratio except for the Fe6N3 clusters. The (Fe2N)m (m?=?1–4) and Fe9N3 clusters exhibit more kinetic stabilities than pure iron clusters. The N substitution can decrease the average spin densities of small iron clusters except for the Fe6N2 and Fe8N4 clusters. The Fe–N bonds exhibit certain covalent bond characteristics. 相似文献
19.
利用密度泛函理论在广义梯度近似下研究了GenEu(n=1-13)团簇的生长模式和磁性.结果表明:对于GenEu(n=1-13)团簇的基态结构而言,没有Eu原子陷入笼中.这和SinEu以及其它过渡金属掺杂半导体团簇的生长模式不同.除GeEu团簇外,GenEu(n=2-13)团簇的磁矩均为7μB.团簇的总磁矩与Eu原子的4f轨道磁矩基本相等.Ge、Eu原子间的电荷转移以及Eu原子的5d、6p和6s间的轨道杂化可以增强Eu原子的局域磁矩,却不能增强团簇总磁矩. 相似文献
20.
New cluster complexes of iron [Fe 3Q(AsCp*)(CO) 9] (Q = Se, Te, Cp* = C 5(CH 3) 5) are synthesized with the square pyramidal cluster core Fe 3QAs. A suitable procedure of the synthesis of known heterochalcogenide [Fe 3QS(CO) 9] clusters is developed. Monosubstituted [Fe 3Q(AsCH 3)(CO) 8(PPh 3)] and disubstituted [Fe 3Q(AsCH 3)(CO) 7(PPh 3) 2] clusters formed in the reactions of [Fe 3Q(AsCH 3)(CO) 9] with PPh 3 are studied. In monosubstituted clusters, the phosphine ligand is coordinated in the axial position to the Fe atom in the base of the Fe 3QAs square pyramid, while in disubstituted clusters, both phosphine ligands coordinate the Fe atoms in the pyramid base, one ligand being in the axial and another one in the equatorial position. The NMR data support the possibility of migration of the Fe-Fe bonds in a triangle in the cluster core in the case of disubstituted clusters. 相似文献
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