金钯二元小团簇的几何结构与电子性质

在UBP86/LANL2DZ和UB3LYP/def2-TZVP水平下详细研究了AumPdn(m+n≤6)团簇的几何结构和电子性质.阐明了团簇的结构特征、平均结合能、垂直电离势、垂直电子亲和能、电荷转移以及成键特征.除单取代混合团簇(AunPd和AuPdn,n=5或6)外,五和六原子混合团簇中钯原子趋于聚集到一起形成Pdcore,金原子分布在Pdcore周围形成PdcoreAushell结构.含一个和两个钯原子团簇的电子性质与纯金团簇类似,呈现一定奇偶振荡.混合团簇的电子性质,如最高占据分子轨道(HOMO),最低未占据分子轨道(LUMO),垂直电离势,垂直电子亲和能,Fermi能级和化学硬度等均与团簇空间结构和金、钯原子数之比直接相关.混合团簇中存在钯原子到金原子间的电荷转移,表明团簇中存在明显金钯间成键作用.分析团簇的电荷分布、前线轨道和化学硬度表明,金钯混合团簇对小分子如O2、H2和CO等的反应活性要强于纯金团簇.     

小镍团簇Nin(n=2～6)电子结构和拓扑分析

在UBP86/TZVP水平上计算了小镍团簇(Ni<,n>,n=2～6)的稳定基态结构并用自然键轨道(NBO)和分子中的原子量子理论(QTAIM)分析了这些团簇的电子结构.计算结果表明,Ni团簇基态结构具有较高自旋多重度.QTAIM分析表明镍团簇中Ni-Ni键均为金属键.除Ni<,2>团簇中Ni-Ni键为纯粹的σ键外,其...     

Au@Gen (n=2-9)团簇的几何结构和电子性质的理论研究

本文选用密度泛函B3LYP方法在Lan L2DZ基组上对Au Gen+(n=2~9)团簇的几何结构和电子性质进行了理论研究,其中包括结构优化、平均键能、HOMO-LUMO能隙和电荷转移等。结果表明,随着锗原子数的不断增加,这些掺杂团簇逐渐形成了三维立体结构,并发现Au Ge7+和Au Ge9+两个掺杂团簇是相对稳定的,而且这些掺杂团簇的电荷转移主要是由金原子到锗原子骨架上。此外,还模拟了这些掺杂团簇的红外光谱,为以后实验研究提供有价值的理论参考。     

金镍六原子团簇吸附CO的密度泛函研究

在UBP86/LAN2DZ水平上计算了金镍二元团簇(AunNi6-n,n=0～6)吸附CO的稳定构型和相关性质.计算结果表明,AunNi6-nCO团簇的最低能量结构是在AunNi6-n团簇最低能量结构或亚稳态结构基础上吸附CO分子而形成.优化结构中C-O键长表明,吸附后的CO没有解离,即CO分子在AunNi6-n团簇表...     

Au12M (M=Na,Mg, Al,Si, P,S, Cl)团簇的结构、稳定性和电子性质

采用基于密度泛函理论的第一性原理方法系统地研究了Au12M(M=Na,Mg,Al,Si,P,S,Cl)团簇的结构、稳定性和电子性质.对团簇的平均结合能、镶嵌能、垂直离化势、最高占据分子轨道(HOMO)和最低未占据分子轨道(LUMO)的能级差、电荷布居分析、自然键轨道(NBO)进行了计算和讨论.对于Au12M(M=Na,Mg,Al)团簇,它们形成了内含M原子的最稳定的笼状结构.然而对于Au12M(M=Si,P,S,Cl)团簇,它们却形成了以M元素为顶点的稳定锥形结构.在这些团簇中发现Au12S团簇相对是最稳定的,这是由于Au12S团簇形成了稳定的满壳层的电子结构.自然电荷布居分析表明:对于所有的Au12M(M=Na,Mg,Al,Si,P,S,Cl)团簇电荷总是从Au原子转向M原子.自然键轨道和HOMO分析表明Au12M团簇中发生了Au原子的s-d轨道和M原子的p轨道间的杂化现象.     

CO在M55（M=Cu,Ag,Au）团簇上吸附的密度泛函研究

在全电子相对论BVP86/DNP水平下对CO在Au55,Ag55和Cu55团簇上的吸附进行了比较研究,并考察了电荷对吸附的影响.计算结果表明,CO在Au55团簇上吸附能最大,其次为Cu55团簇,最弱的为Ag55团簇.团簇电荷对C—O键活化和CO与团簇表面原子成键影响较小.金团簇的电荷对吸附能影响较大,而银和铜团簇的电荷对吸附能影响较小.CO吸附到团簇上导致团簇上电子向CO转移.C—O键活化强度与吸附位置密切相关,其中孔位吸附导致C—O键活化程度最大,最弱的为顶位吸附.CO在金团簇上吸附具有较好选择性,而在银和铜团簇上吸附无选择性.     

Sc12Co和Sc12Ni团簇的几何结构、磁性和光谱特性的理论研究

基于密度泛函理论和卡利普索结构预测方法,在B3PW91/LanL2DZ水平下,系统研究了Sc₁₃,Sc₁₂Co和Sc₁₂Ni团簇的几何结构、磁性和光谱特性.结果表明,Sc₁₃基态拥有高对称性的二十面体I_h点群对称结构,Sc₁₂Co和Sc₁₂Ni团簇基态结构是分别以Co和Ni为中心的畸变二十面体结构.基于上述基态结构,电荷转移分析发现电荷从Sc原子向Ni或Co原子转移.磁性分析表明Sc₁₃团簇的高磁性主要源于Sc—Sc之间的铁磁性耦合和较大的自旋劈裂.对于Sc₁₂Co和Sc₁₂Ni团簇,Sc—Ni和Sc—Co各原子之间的反铁磁性耦合、较小的自旋劈裂及原子间的电荷转移量是磁性偏低的原因.而且,总磁矩主要来源于Sc-3d轨道上的自旋磁矩贡献,4s和4p轨道上的自旋磁矩贡献非常小.最后,研究发现Sc₁₂Co和Sc₁₂Ni团簇的红外和拉...     

六核钽铑二元混合簇合物的几何和电子结构

采用密度泛函理论对六核钽、铑八面体纯簇及其混合簇的几何结构和电子性质进行了研究.计算结果表明:大部分钽铑混合簇稳定构型的对称性均较低,为C1或Cs点群,只有[Ta2Rh4Cl4H8(CN)6]4-团簇的稳定构型对称性较高,为C2h或C4v点群;混合簇的最高占据分子轨道(HOMO)与最低未占据分子轨道(LUMO)能隙(ΔEH-L)均较小,介于0.52-1.00eV之间;混合簇的前线轨道主要由骨架金属原子的d电子贡献,随着Rh原子替代Ta原子个数的递增,Ta—Rh键对混合簇稳定构型所起作用逐渐增加,Ta—Ta键所起作用减小,而Rh—Rh键为非键或反键性质.     

Sn_nSm(n=1～9)团簇结构稳定性与磁学性质的理论研究

采用Saunders全局优化随机踢球模型与密度泛函理论相结合的方法,在B3LYP/SDD理论水平下研究了锡基原子团簇Sn_n(n=2~10)及锡基稀土原子钐掺杂团簇Sn_nSm(n=1~9)的几何结构、稳定性、电子性质和磁性.结果表明,团簇Sn_nSm(n=1~9)中掺杂的钐原子通常位于主团簇的表面,掺杂团簇的基态结构更倾向于具有较高对称性的三维结构;二元锡基混合团簇的平均结合能变大,稳定性增强,这主要归因于Sn—Sm键比Sn—Sn键的键能大,具有更强的相互作用;掺杂团簇具有较高的磁性,其总磁矩主要源自于钐原子4f电子的贡献;随着团簇尺寸的增加,二元团簇的总磁矩呈现出趋于饱和的现象.     

Aun(n=2-9)团簇与乙醇分子相互作用的第一性原理研究

利用密度泛函理论研究了Au_n(n=2-9)团簇吸附一个乙醇分子的结构和电子性质. 研究结果表明: Au_n(n=2-9)团簇的最稳定构型为二维平面结构, Au6团簇最稳定; 吸附过程是通过金团簇上一个特定的金原子与乙醇分子中氧原子相互作用完成, 形成了20种稳定构型; 金原子的配位数对吸附作用影响明显; 作为吸附主体的金团簇和被吸附的乙醇分子在吸附前后构型无明显变化, 它们之间为弱相互作用.     

Density functional study of structural and electronic properties of small bimetallic silver-nickel clusters

Theoretical study on the structure and electronic properties of small AgmNip (m + p < or = 6) clusters has been carried out in the framework of density functional theory. Structural features, cohesive energies, vertical ionization potentials, and charge transfers are evaluated for each Ag/Ni ratio. In all the AgmNip clusters, the nickel atoms are brought together, yielding a maximum of Ni-Ni bonds, and the silver atoms are located around a Ni core with a maximum of Ag-Ni bonds. The ionization potential and the highest occupied molecular orbital shape are directly related to the two- or three-dimensional character of the cluster's geometry. A very low electronic charge transfer from Ni to Ag is found, and the magnetic moment is located on Ni atoms but with a low spin polarization on silver in the Ni-rich clusters.     

Determination of structures, stabilities, and electronic properties for bimetallic cesium-doped gold clusters: a density functional theory study

The equilibrium geometric structures, stabilities, and electronic properties of bimetallic Au(n)Cs (n = 1-10) and pure gold Au(n) (n ≤ 11) clusters have been systematically investigated by using density functional theory with meta-generalized gradient approximation. The optimized geometries show that one Au atom capped on Au(n-1)Cs structures and Cs atom capped Au(n) structures for different sized Au(n)Cs (n = 1-10) clusters are two dominant growth patterns. Theoretical calculated results indicate that the most stable isomers have three-dimensional structures at n = 4 and 6-10. Averaged atomic binding energies, fragmentation energies, and second-order difference of energies exhibit a pronounced even-odd alternations phenomenon. The same even-odd alternations are found in the highest occupied-lowest unoccupied molecular orbital gaps, vertical ionization potential, vertical electron affinity, and hardnesses. In addition, it is found that the charge in corresponding Au(n)Cs clusters transfers from the Cs atom to the Au(n) host in the range of 0.851-1.036 electrons.     

Glucose interaction with Au,Ag, and Cu clusters: Theoretical investigation

Interactions of α‐D ‐glucose with gold, silver, and copper metal clusters are studied theoretically at the density functional theory (CAM‐B3LYP) and MP2 levels of theory, using trimer clusters as simple catalytic models for metal particles as well as investigating the effect of cluster charge by studying the interactions of cationic and anionic gold clusters with glucose. The bonding between α‐D ‐glucose and metal clusters occurs by two major bonding factors; the anchoring of M atoms (M = Cu, Ag, and Au) to the O atoms, and the unconventional M…H? O hydrogen bond. Depending on the charge of metal clusters, each of these bonds contributes significantly to the complexation. Binding energy calculations indicate that the silver cluster has the lowest and gold cluster has the highest affinity to interact with glucose. Natural bond orbital analysis is performed to calculate natural population analysis and charge transfers in the complexes. Quantum theory of atoms in molecules was also applied to interpret the nature of bonds. © 2012 Wiley Periodicals, Inc.     

Geometrical and electronic structures of Au(m)Ag(n) (2 < or = m + n < or = 8)

The structural and electronic properties of Au(m)Ag(n) binary clusters (2 < or = m + n < or = 8) have been investigated by density functional theory with relativistic effective core potentials. The results indicate that Au atoms tend to occupy the surface of Au(m)Ag(n) clusters (n > or = 2 and m > or = 2). As a result, segregation of small or big bimetallic clusters can be explained according to the atomic mass. The binding energies of the most stable Au(m)Ag(n) clusters increase with increasing m+n. The vertical ionization potentials of the most stable Au(m)Ag(n) clusters show odd-even oscillations with changing m+n. The possible dissociation channels of the clusters considered are also discussed.     

Geometric, electronic, and bonding properties of AuNM (N = 1-7, M = Ni, Pd, Pt) clusters

Employing first-principles methods, based on density functional theory, we report the ground state geometric and electronic structures of gold clusters doped with platinum group atoms, Au(N)M (N = 1-7, M = Ni, Pd, Pt). The stability and electronic properties of Ni-doped gold clusters are similar to that of pure gold clusters with an enhancement of bond strength. Due to the strong d-d or s-d interplay between impurities and gold atoms originating in the relativistic effects and unique properties of dopant delocalized s-electrons in Pd- and Pt-doped gold clusters, the dopant atoms markedly change the geometric and electronic properties of gold clusters, and stronger bond energies are found in Pt-doped clusters. The Mulliken populations analysis of impurities and detailed decompositions of bond energies as well as a variety of density of states of the most stable dopant gold clusters are given to understand the different effects of individual dopant atom on bonding and electronic properties of dopant gold clusters. From the electronic properties of dopant gold clusters, the different chemical reactivity toward O(2), CO, or NO molecule is predicted in transition metal-doped gold clusters compared to pure gold clusters.     

First‐Principles Study toward CO Adsorption on Au/Ni Surface Alloys

The introduction of a second metal, gold, into a nickel matrix can effectively improve the catalytic performance and thermal stability of the catalysts toward steam reforming of methane. To investigate the effect of Au on the adsorption properties and electronic structure of the Ni(111) surface, we chose CO as a probe molecule and examined CO adsorption on various Au/Ni surfaces. It was revealed that Au addition weakened the absorbate–substrate interactions on the Ni(111) surface. With increasing gold concentration, the binding energy declines further. The variation of the binding energies has been interpreted by exploring the electronic structure of surface nickel atoms. The effect of gold can be quantitatively characterized by the slopes of the fitting equations between the binding energy and the number of gold atoms surrounding the adsorption site. Our results show that the binding energy at top sites can be approximately estimated by counting the number of surrounding gold atoms. On one specific surface, the relative magnitude of the binding energy can be simply judged by the distance between gold and the geometrical center of the adsorption site. This empirical rule holds true for C, H, and O adsorption on the Au/Ni surface. It may be applicable to a system in which a doped atom of larger atomic size is incorporated into the host metal surface by forming a surface alloy.     

The stability of small helical gold nanorods: a relativistic density functional study

Multistrand 7-1 helical Au(24), Au(32), and Au(40) structures with three, four, and five gold atoms in the central strand and 21, 28, and 35 gold atoms in the coaxial tube are investigated using relativistic density functional theory. We demonstrate that these helical gold nanorods are stable structures with a rather large HOMO-LUMO gap, a large binding energy per atom, a very large vertical dissociation energy, and an extremely large electron affinity. On the basis of the atomic charges and the nature of the frontier orbitals, they are also expected to have strong selective reactivity toward electrophiles and nucleophiles. Furthermore, we show that these helical Au(n) structures and, in particular, the helical Au(40) structure are competitive energetically and chemically with respect to alternate cage and compact Au(n) structures. We consider two fragmentations of the helical Au(40) structure and perform a density of states analysis to examine both charge transfer and electronic polarization.     

Al7Ag and Al7Au clusters with large highest occupied molecular orbital-lowest unoccupied molecular orbital gap

The candidate structures for the ground-state geometry of the Al(7)M (M = Li, Cu, Ag, and Au) clusters are obtained within the spin-polarized density functional theory. Absorption energy, vertical ionization potential, vertical electron affinity, and the energy gap between the highest occupied molecular orbital (HOMO) level and the lowest unoccupied molecular orbital (LUMO) level have been calculated to investigate the effects of doping. Doping with Ag or Au can lead to a large HOMO-LUMO gap, low electron affinity, and increased ionization potential of Al(7) cluster. In the lowest-energy structure of the Al(7)Au cluster, the Al atom binding to the Al(6)Au acts monovalent and the other six Al atoms are trivalent. Thus, the Al(7)Au cluster has 20 valence electrons, and its enhanced stability may be due to the electronic shell closure effect.     

[Ca(NH2)2]n (n＝1～5)团簇的密度泛函理论研究

用密度泛函理论(DFT)的杂化密度泛函B3LYP方法在6-31G*基组水平上对[Ca(NH2)2]n (n＝1～5)团簇各种可能的构型进行几何结构优化, 预测了各团簇的最稳定结构. 并对最稳定结构的振动特性、成键特性、电荷特性等进行了理论研究. 结果表明: 团簇易形成环状结构, 以金属Ca原子团簇作为骨架, NH2基结合在金属团簇骨架上, 并主要是Ca—N成键和Ca—Ca成键. 团簇中Ca—N键长为0.225～0.257 nm, Ca—Ca键长为0.312～0.354 nm, N—H键长为0.102～0.103 nm, H—N—H键角为102.9°～104.2°; 团簇中Ca原子的自然电荷在1.657e～1.720e之间, N原子的自然电荷在－1.543e～－1.592e之间, H原子的自然电荷在0.349e～0.367e之间, Ca原子和NH2基之间相互作用呈现较强的离子性;对比团簇和晶体的结构及IR谱表明, NH2基在团簇和晶体中的结构基本一致.