Chiral structures and tunable magnetic moments in 3d transition metal doped Pt6 clusters

The structural, electronic, and magnetic properties of transition metal doped platinum clusters MPt6 （M=Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn） are systematically studied by using the relativistic all-electron density functional theory with the generalized gradient approximation. Most of the doped clusters show larger binding energies than the pure Pt7 cluster, which indicates that the doping of the transition metal atom can stabilize the pure platinum cluster. The results of the highest occupied molecular orbital （HOMO） lowest unoccupied molecular orbital （LUMO） gaps suggest that the doped clusters can have higher chemical activities than the pure Pt7 cluster. The magnetism calculations demonstrate that the variation range of the magnetic moments of the MPt6 clusters is from 0 μB to 7 μB, revealing that the MPt6 clusters have potential utility in designing new spintronic nanomaterials with tunable magnetic properties.     

A DFT study for adsorption of CO on Ni,Pd and Pt atoms doped (7, 0) boron nitride nanotube

By using density functional theory calculations, we investigated the structural, electronic and magnetic properties of carbon monoxide (CO) adsorption on the pure, Ni, Pd and Pt doped atoms in zigzag single-walled (7, 0) boron nitride nanotubes (BNNTs). The results indicated that compared to the pure (7, 0) BNNTs, replacing B atom by Ni, Pd and Pt atoms can significantly increase the adsorption energy of CO gas on the BNNTs. The adsorption energies of CO gas on the pure (7, 0) Ni, Pd and Pt doped (7, 0) BNNTs are ?0.2013, ?1.746, ?1.593 and ?2.257 eV, respectively. Our results revealed that in comparison with the pure (7, 0) BNNTs, CO gas is chemisorbed on the transition metal doped (7, 0) BNNTs with the appreciable adsorption energy. In addition, it was found that by doping these atoms, band gap energy of the pure (7, 0) BNNTs is considerably decreased. These observations suggested that the Pt doped (7, 0) BNNTs can be introduced as a promising candidate in gas sensor devices for detecting CO gas.     

Electronic and magnetic properties of free and supported transition metal clusters

The spin-polarized relativistic version of the multiple scattering or the Korringa–Kohn–Rostoker method for electronic structure calculations has been used to study the electronic and magnetic properties of free and supported transition metal clusters. Corresponding results are presented for the spin- and spin–orbit-induced orbital magnetic moments in free Fe and FePt clusters. For both systems a pronounced enhancement is found for the spin as well as for the orbital moments compared with the corresponding bulk value which diminishes in an oscillatory fashion with increasing cluster size. Corresponding investigations on small Co clusters deposited on a Pt (111) surface also revealed a strong dependence of the magnetic properties on the cluster size and shape. A comparison of our theoretical results with available experimental data led to rather satisfying agreement.     

The 13-atom encapsulated gold cage clusters

The structure and the magnetic moment of transition metal encapsulated in a Au 12 cage cluster have been studied by using the density functional theory.The results show that all of the transition metal atoms(TMA) can embed into the Au 12 cage and increase the stability of the clusters except Mn.Half of them have the I h or O h symmetry.The curves of binding energy have oscillation characteristics when the extra-nuclear electrons increase;the reason for this may be the interaction between parity changes of extra-nuclear electrons and Au atoms.The curves of highest occupied molecular orbital-lowest unoccupied molecular orbital(HOMO-LUMO) gap also have oscillation characteristics when the extra-nuclear electrons increase.The binding energies of many M@Au 12 clusters are much larger than that of the pure Au 13 cluster,while the gaps of some of them are less than that of Au 13,so maybe Cr@Au 12,Nb@Au 12,and W@Au 12 clusters are most stable in fact.For magnetic calculations,some clusters are quenched totally,but the Au 13 cluster has the largest magnetic moment of 5 μ B.When the number of extra-nuclear electrons of the encapsulated TMA is even,the magnetic moment of relevant M@Au 12 cluster is even,and so are the odd ones.     

Density functional calculations on 13-atom Pd12M （M= Sc-Ni） bimetallic clusters

The geometric structures,electronic and magnetic properties of the 3d transition metal doped clusters Pd12M(M=Sc-Ni) are studied using the semi-core pseudopots density functional theory.The groundstate geometric structure of the Pd12M cluster is probably of pseudoicosahedron.The Ih-Pd12M cluster has the most thermodynamic stability in five different symmetric isomers.The energy gap shows that Pd12M cluster is partly metallic.Both the absolutely predominant metal bond and very weak covalent bond might exist in the Pd12M cluster.The magnetic moment of Pd12M varies from 0 to 5 μB,implying that it has a potential application in new nanomaterials with tunable magnetic properties.     

Density-functional investigation of 3d,4d,5d impurity doped Au6 clusters

The general features of the geometries and electronic properties for 3d,4d,and 5d transition-metal atom doped Au 6 clusters are systematically investigated by using relativistic all-electron density functional theory in the generalized gradient approximation(GGA).A number of structural isomers are considered to search the lowest-energy structures of M@Au 6 clusters(M=3d,4d and 5d transition-metal atoms),and the transition metal atom locating in the centre of an Au 6 ring is found to be in the ground state for all the M@Au 6 clusters.All doped clusters,expect for Pd@Au 6,show large relative binding energies compared with a pure Au 7 cluster,indicating that doping by 3d,4d,5d transition-metal atoms could stabilize the Au 6 ring and promote the formation of a new binary alloy cluster.     

A computational DFT analysis of OH chemisorption on catalytic Pt(111) nanoparticles

In this article, various energies and geometries of pure platinum nanoparticles and those of platinum nanoparticles with adsorbed OH were investigated. Fourteen different platinum clusters of 3–40 atoms were studied using spin-unrestricted density functional theory (DFT) with a double numerical plus polarization basis set. This range of sizes gave enough information for establishing the general trends that were the primary goal of the study. Three different shapes of platinum clusters were presented, and the effect of cluster size on binding energy, total energy, and HOMO–LUMO energy gap was investigated. Subsequently, same calculations were performed for those selected Pt clusters with OH adsorbate on the surface. The results show that the stability of both the pure clusters and the clusters with adsorbed OH molecule increases with an increase of cluster size. This fact indicates that direct influence of the size of Pt cluster on the reaction rate is possible, and the understanding of how cluster size would affect binding energy is important. As expected, the effect of cluster size on total energy of molecule was shown to be a linear function independent of cluster type. We also found that optimized (stable) Pt clusters were bigger in size than that of the initial clusters, or clusters with bulk geometry.     

合金团簇(FeCr)n中的非共线磁序和自旋轨道耦合效应

利用密度泛函理论对合金团簇(FeCr)_n (n≤6)的几何结构、稳定性和磁性进行了系统的研究. 研究结果表明, 对n≤3的合金团簇, 其基态具有共线的反铁磁序; 而对于n≥4 的合金团簇, 其基态具有非共线磁序, 因此在n=4时体系发生了共线磁序向非共线磁序的“相变”. 此外, 虽然3d过渡金属原子中电子的自旋轨道耦合效应比较弱, 但计算结果表明对于某些小尺寸的合金团簇其轨道磁矩不能忽略. 对非共线磁性团簇的成键性质以及产生磁序“相变”的物理起源进行了详细讨论. 关键词： n合金团簇')" href="#">(FeCr)_n合金团簇 密度泛函理论 非共线磁序 自旋轨道耦合效应     

Structures and electronic properties of M@Au<Subscript>6</Subscript> (M=Al,Si, P,S, Cl,Ar) clusters: a density functional theory investigation

The geometries and electronic properties of the 3p electrons atoms doped gold cluster: M@Au₆ clusters (M=Al, Si, P, S, Cl, Ar) have been systematically investigated by using relativistic all-electron density functional theory (VPSR) and scalar relativistic effective core potential Stuttgart/Dresden (SDD) basis. Generalized gradient approximation in the Perdue-Burke-Ernzerhof (PBE) functional form is chosen for geometry optimization. A number of new isomers are obtained for neutral M@Au₆ clusters. Both PBE/VPSR and PBE/SDD methods give similar lowest energy structure of each M@Au₆cluster. With the exception of Ar@Au₆, all doped clusters show larger relative binding energies compared with pure Au₇ cluster. It is found that all the ground-state structures of the M@Au₆ clusters prefer the low symmetry structures, which is very different to the 3d transition-metal impurity doped Au₆ clusters. Our results are in excellent agreement with available experiment data.     

硅团簇自旋电子器件的理论研究

利用过渡金属掺杂的硅基团簇, 构建了一种自旋分子结; 并利用第一性原理方法, 对其电子自旋极化输运性质进行了研究. 计算表明, 通过过渡金属掺杂可以有效地产生自旋极化电流, 磁性金属Fe和非磁性金属Cr和Mn掺杂的体系呈现出较明显的自旋极化透射现象, 但分子结的自旋极化输运能力与团簇孤立状态下的磁矩无一致性.从Sc到Ni的掺杂, 体系的自旋极化透射能力先增大后迅速减小, 在Fe掺杂的Si₁₂团簇中出现最大值. 关键词： 硅团簇 自旋极化输运 密度泛函理论 非平衡格林函数     

Magic numbers in metallo-inorganic clusters: chromium encapsulated in silicon cages

A systematic theoretical study of the equilibrium geometries and total energies of Cr encapsulated in Si clusters reveals that Cr@Si(12) is more stable than its neighbors. The origin of this enhanced stability is consistent with the 18-electron sum rule commonly used in the synthesis of stable chemical complexes, and may provide a criterion for a systematic search of magic numbers in metalloinorganic clusters. The 6 mu(B) magnetic moment of the caged Cr atom, the largest among the 3d transition metal atoms, is completely quenched. This effect of caging on the properties of transition metal atoms may lead to the synthesis of novel cluster based materials.     

The influence of the composition of eight-atom Pt–Ir clusters on the magnetic properties

The energetic stability, electronic structure and magnetic properties of Pt_8–nIr_n clusters have been investigated by employing the spin-polarised generalised gradient approximation. The cubic structure is expected to be the effective building block in Ir-rich clusters after optimisation extensively. The average binding energy of all the clusters presents the linear increment trend with iridium atoms, due to the stronger interaction between Ir atoms than Pt atoms. Bader charge analysis shows how tiny charge transfers from iridium to platinum. The atomic moments of Ir are larger than that of Pt, and the Ir-rich clusters show greater moments than the Pt-rich cluster, with the exception of Ir₈ and Ir₇Pt. A unique magnetic property is found in the Pt₄Ir₄ cluster, where two Pt atoms show antiferromagnetic alignment and the other atoms are found to be aligned ferromagnetically.     

Probing the structural,electronic and magnetic properties of small Au4M (M = Sc–Zn) clusters

Density-functional method PW91 has been selected to investigate the structural, electronic and magnetic properties of Au₄M (M =Sc–Zn) clusters. Geometry optimisations show that the M atoms in the ground-state Au₄M clusters favour the most highly coordinated position. The ground-state Au₄M clusters possess a solid structure for M = Sc and Ti and a planar structure for M = V–Zn. The characteristic frequency of the doped clusters is much greater than that of pure gold cluster. The relative stability and chemical activity are analysed by means of the averaged binding energy and highest occupied molecular orbital and lowest unoccupied molecular orbital energy gap for the lowest energy Au₄M clusters. It is found that the dopant atoms can enhance the thermal stability of the host cluster except for Zn atom. The Au₄Ti, Au₄Mn and Au₄Zn clusters have relatively higher chemical stability. The vertical detachment energy, electron affinity and photoelectron spectrum are calculated and simulated theoretically for all the ground-state structures. The magnetism calculations reveal that the total magnetic moment of Au₄M cluster is mainly localised on the M atom and vary from 0 to 5 μ_B by substituting an Au atom in Au₅ cluster with different transition-metal atoms.     

Effect of sulphur doping on manganese clusters: an ab initio study

We report a structural, electronic and magnetic analysis of minimal Mn_nS clusters, n = 1–13, from ab initio calculations. Total geometry optimizations were performed by considering compact manganese clusters, doped with a single sulphur atom. The doping was added to the cluster by considering substitution, interstitial and adsorbed positions. To further investigate the influence of the sulphur doping on the magnetic properties of manganese clusters, we performed non collinear magnetic calculations within the local spin density approximation (LSDA) for the exchange-correlation. We find that the electronic properties can be better controlled when the cluster is doped with a sulphur atom, and less size dependent. There are no differences in the magnetic properties of doped and non-doped clusters, except for n=7 and 8, in which the total magnetic moment per atom are smaller in doped clusters.     

First principles study of the magnetism driven by cation defects in CeO₂:the important role of O2p states

The magnetism driven by cation defects in undoped CeO 2 bulk and thin films is studied by the density functional theory corrected for on-site Coulomb interactions (DFT+U) with U = 5 eV for the Ce4f states and U = 7 eV for the O2p states. It is found that the Ce vacancies can induce a magnetic moment of the ～ 4 μ B /supercell, which arises mainly from the 2p hole state of the nearest neighbouring O atom (～ 1 μ B on per oxygen) to the Ce vacancy. The effect of the methodology is investigated, indicating that U = 7 eV for the O2p state is necessary to obtain the localized O2p hole state in defective ceria with cation vacancies.     

Evolution of the 251 cm^-1 infrared phonon mode with temperature in Ba_0.6K_0.4Fe₂As₂

The far-infrared optical reflectivity of an optimally doped Ba1-xKxFe2As2(x =0.4) single crystal is measured from room temperature down to 4 K. We study the temperature dependence of the in-plane infrared-active phonon at 251 cm-1 . This phonon exhibits a symmetric line shape in the optical conductivity, suggesting that the coupling between the phonon and the electronic background is weak. Upon cooling down, the frequency of this phonon continuously increases, following the conventional temperature dependence expected in the absence of a structural or magnetic transition. The intensity of this phonon is temperature independent within the measurement accuracy. These observations indicate that the structural and magnetic phase transition might be completely suppressed by chemical doping in the optimally doped Ba0.6K0.4Fe2As2 compound.     

Density functional study on structural and electronic properties of bimetallic gold--yttrium clusters: comparison with pure gold and yttrium clusters

Employing first-principles methods, based on the density functional theory, this paper investigates the ground state geometric and electronic properties of pure gold clusters, pure yttrium clusters and gold clusters doped each with one yttrium atom. It is shown that the average bond lengths in the Augold--yttrium bimetallic cluster, density functional theory, HOMO--LUMO gap, equilibrium structureProject supported by the Education Committee of Chongqing (Grant No KJ051105) and the National Natural Science Foundation of China (Grant No 10276028).3640, 3640B, 3120A, 3130J9/1/2007 12:00:00 AMEmploying first-principles methods, based on the density functional theory, this paper investigates the ground state geometric and electronic properties of pure gold clusters, pure yttrium clusters and gold clusters doped each with one yttrium atom. It is shown that the average bond lengths in the Augold--yttrium bimetallic cluster, density functional theory, HOMO--LUMO gap, equilibrium structureProject supported by the Education Committee of Chongqing (Grant No KJ051105) and the National Natural Science Foundation of China (Grant No 10276028).3640, 3640B, 3120A, 3130J9/1/2007 12:00:00 AMEmploying first-principles methods, based on the density functional theory, this paper investigates the ground state geometric and electronic properties of pure gold clusters, pure yttrium clusters and gold clusters doped each with one yttrium atom. It is shown that the average bond lengths in the Au$_{n - 1}$Y($n \le $9) bimetallic clusters are shorter than those in the corresponding pure gold and yttrium clusters. The most stable isomers of the yttrium-doped gold clusters tend to equally delocalize valence s, p and d electrons of the constituent atoms over the entire structure. The Y atom has maximum number of neighbouring Au atom, which tends to be energetically favourable in the lowest-energy equilibrium structures, because the Au--Y bond is stronger than the Au-Au bond. The three-dimensional isomers of Au$_{n - 1}$Y structures are found in an early appearance starting at $n$=5 (Au$_{4}$Y). Calculated vertical ionization potential and electron affinities as a function of the cluster size show odd-even oscillatory behaviour, and resemble pure gold clusters. However, one of the most striking feature of pure yttrium clusters is the absence of odd-even alternation, in agreement with mass spectrometric observations. The HOMO--LUMO gap of Au$_{3}$Y is the biggest in all the doped Au$_{n - 1}$Y($n \le $9) bimetallic clusters.     

Physical properties of metal cluster compounds I: Magnetic measurements on high-nuclearity nickel and platinum carbonyl clusters

Metal-carbonyl cluster compounds are composed of macromolecules that consist of a core of metal atoms coordinated by a “shell” of CO ligands. We present susceptibility and high-field magnetization measurements on various high-nuclearity platinum and nickel clusters. The compounds display very unusual low-temperature magnetic behaviour, which we ascribe to quantum-size-effects arising from the discreteness of the electronic energy levels due to the small dimensions of the metal clusters (10–40 atoms). We compare our results with predictions from molecular orbital calculations.     

非晶态合金Fe80P20局域结构和性质的量子化学研究

利用原子簇模型Fe_4P简化了非晶态合金Fe_(80)P_(20)的局域结构,设计了四方锥、三角双锥、四面体及平面五边形等十几种构型,对其二、四重态分别进行密度泛函(DFT)优化计算,经过频率验证,获得五种稳定构型。从所得优化构型的键长和键级,可以发现原子簇Fe4P较好地反映了非晶态合金Fe_(80)P_(20)的局域结构。考察了各构型间的过渡转化情况,发现二重态构型的稳定性要好于四重态。分析各构型的能量、成键及电子转移情况,发现与P原子成键的Fe原子个数对这些性质影响较为明显。与P原子成键的Fe原子个数越多,体系的能量就越低,越容易存在；P原子的得电子能力随着与其成键Fe原子个数增多而减少,甚至会将失去自身电子转移到金属原子上。同时通过3d轨道布居数,讨论了原子簇的空穴数及磁学性质。