多体展开势能函数在碳族元素原子簇研究中的应用 Ⅲ.锗原子簇的结构和相对稳定性

基于从晶体锗确立的多体展开势能函数,本文通过坐标完全优化,发现小的锗原子簇分子(Ge_2—Ge_(14))倾向于形成密堆积结构,表面原子分布以蝶形四元环(D_(2d))为主;常见立方晶体“微观晶体碎片”的分层优化结果表明,在Ge_(15)～Ge_(100)范围内,多数壳层的原子到分子中心的距离均受到压缩,且以畸变的简单立方、面心立方及体心立方较为稳定;在这些畸变密堆积结构中,表面原子向内压缩最为严重,使整个分子趋于球形化.较为开放的金刚石类层状原子簇只有当所含原子数达数百以上时才可能相对更为稳定.     

多体展开势能函数在碳族元素原子簇研究中的应用III. 锗原子族的结构和相对稳定性

基于从晶体锗确立的多体展开势能函数, 本文通过坐标完全优化, 发现小的锗原子簇分子(Ge~2~Ge~14)倾向于形成密堆积结构, 表面原子分布以蝶形四元环(D~2d)为主; 常见立方晶体“微观晶体碎片”的分层优化结果表明, 在Ge~15~Ge~100范围内, 多数壳层的原子到分子中心的距离均受到压缩, 且以畸变的简单立方、面心立方及体心立方较为稳定; 在这些畸变密堆积结构中, 表面原子向内压缩最为严重, 使整个分子趋于球形化。较为开放的金刚石类层状原子族只有当所含原子数达数百以上时才可能相对更为稳定。     

多体展开势能函数在碳族元素原子簇研究中的应用III. 锗原子族的结构和相对稳定性

基于从晶体锗确立的多体展开势能函数, 本文通过坐标完全优化, 发现小的锗原子簇分子(Ge~2~Ge~14)倾向于形成密堆积结构, 表面原子分布以蝶形四元环(D~2d)为主; 常见立方晶体“微观晶体碎片”的分层优化结果表明, 在Ge~15~Ge~100范围内, 多数壳层的原子到分子中心的距离均受到压缩, 且以畸变的简单立方、面心立方及体心立方较为稳定; 在这些畸变密堆积结构中, 表面原子向内压缩最为严重, 使整个分子趋于球形化。较为开放的金刚石类层状原子族只有当所含原子数达数百以上时才可能相对更为稳定。     

银团簇结构与特性的分子动力学研究

用分子动力学方法模拟了银团簇的结构与力能学.计算模拟中使用了一种基于第一性原理的原子间互作用多体势函数.通过分子动力学模拟确定了银微团簇(原子个数3～13)的稳态结构;模拟了原子个数为13～141的银FCC晶体结构理想球形团簇的力能学,发现球形银团簇形成三雏紧密结构;计算了平均结合能,给出了结合能随团簇原子数N的变化图,发现随N增大团簇结合能逐渐接近块材的数值.     

四核簇离子S42+、Se42+、Te42+、Bi42-、Sn42-和Ge42-的电子结构与化学键

本文用EHMO法计算四核簇离子S_4~(2+)、Se_4~(2+)、Te_4~(2+)、Bi_4~(2-)、Sn_4~(2-)和Ge_4~(2-)的电子结构。讨论了平面正四边形S_4~(2+)、Se_4~(2+)、Te_4~(2+)和Bi_4~(2-)簇离子与蝴蝶形四核原子簇在成键性质上的不同。比较Sn_4~(2-)、Ge_4~(2-)簇离子与P_4、As_4原子簇电子结构的差别,分析Sn_4~(2-)和Ge_4~(2-)稳定性较差的原因。     

锂原子簇结构的分子力学研究

本文采用包含Axilord—Teller三体势的分子力学方法,计算了锂原子簇的平衡几何构型,结果表明,锂原子簇的势能面上存在一些近简并的结构。但最稳定结构与从头算的结果基本一致,同时对气相原子簇的生长模式、簇尺寸增大原子簇平均结合能的变化进行了讨论。     

钼的原子簇化合物研究——一些两核和三核钼原子簇化合物的合成与晶体结构分析

本文总结了作者们研究一系列两核和三核钼原子簇化合物的结果。这些化合物是三核原子簇: (C_5H_7S_2)_3[Mo_3(μ_3-S)_2(μ_2-Cl)_3Cl_6] (Ⅰ); (C_5H_7S_2)_3[Mo_3(μ_3-S)(μ_2-S_2)_3Cl_7] (Ⅱ); Mo_3(μ_3-S)(μ_2-S_2)_3[S_2P(OEt)_2)_3Cl (Ⅲ); (Et_4N)_2[Mo_3(μ_3-O)(μ_2-Cl)_3(Oac)_2Cl_5] (Ⅳ); (C_5H_7S_2)[Mo_3(μ_3-O)(μ_2-Cl)_3(Oac)_3Cl_3] (Ⅴ); 和两核原子簇: (C_5H_7S_2)_3[Mo_2Cl_9] (Ⅵ); M0_2S_4[S_2P(OEt)_2]_2 (Ⅶ)。 本文的第一部分简要地介绍了这些化合物的合成方法。第二部分扼要地给出了这些化合物的晶体与分子结构。簇合物Ⅰ是离子型结构,簇阴离子是双(S)帽三核原子簇,每个Mo原子周围为八面体六配位,Mo—Mo间距为2.617。簇阴离子Ⅱ和簇分子Ⅲ均是单(S)帽三核簇,Mo原子周围为畸变五角双锥构型,Mo—Mo键长分别为2.751和2.725。簇阴离子Ⅳ和Ⅴ均是单(O)帽三核簇,Mo原子周围的配位为畸变八面体,Mo—Mo键长分别为2.597和2.577。化合物Ⅵ是三(μ_2—Cl)桥两核原子簇,其构型为两个共面八面体,Mo—Mo间距为2.707。化合物Ⅶ为双(S)桥两核原子簇,Mo原子周围为四角锥配位,Mo—Mo键长为2.828。 本文的第三部分用简化分子轨道方法分析了三种主要类型的三核钼原子簇中Mo_3体系的M—M键?     

N2O多层膜局域结构的多重散射簇理论研究

利用多重散射簇(multiple scattering cluster, MSC)方法计算了N2O多层膜中氮原子的1s芯态近边X射线吸收精细结构(near edge X-ray absorption fine structure, NEXAFS)谱,首次给出N2O多层膜局域结构的模型. MSC研究显示多层膜中N2O分子以短程有序的分层错位链结构排列,并求得链中相邻分子间距为0.233 nm和相邻分子层之间距离为0.240～0.245 nm.用自洽场离散变分(discrete variation, DV)Xα方法计算的N2O多层膜电子结构支持了MSC的计算结果;阐明了NEXAFS谱中弱结构的物理起源.对N2O多层膜中分子之间相互作用的分析显示N2O多层膜的结构具有分子自组装的特性.     

具有局部松散配位的三核钼簇合物研究:{Mo3(μ3-S)(μ-S)3[S2P(OEt)2]4.P(C6H5)3}.(O86CH2Cl2)的合成和晶体结构

本文报道了具有局部松散配位的三核钼原子簇{Mo3(μ3-S)(μ-S)[S2P(OEt)2]4.P(C6H5)3}.(0.86CH2Cl2)的合成和晶体结构.在CAD-4四圆衍射仪上用Mo Kα射线收集到I≥2σ(I)的衍射点4840个.采用重原子法和差电子密度法解出结构,并用全矩阵最小二乘法修正,最终偏离因子为0.058.簇分子的Mo-Mo键为2.731(1),2.748(1),2.753(1)A,Mo原子和三苯基膦的P原子配位键长为Mo-P2.647(3)A,显著长于一般的Mo-P共价单键.三苯基膦基团在Mo的配位多面体中处于三重桥S原子的对位,表现出与其他此类簇合物的松散配位体配位位置不同.文中概括了此类簇合物的Mo-Mo键和Mo-L的成键情况.     

具有局部松散配位的三核钼簇合物研究——{M0_3(μ-3-S)(μ-S)_3[S_2P(OEt)_2]_4·P(C_6H_5)_3}·(086CH_2Cl_2)的合成和晶体结构

本文报道了具有局部松散配位的三核钼原子簇{Mo_3(μ_3-S)(μ-S)_3[S_2P(OEt)_2]_4·P(C_6H_5)_3}·(0.86CH_2Cl_2)的合成和晶体结构。晶体属三斜晶系,空间群为PI,单胞参数a=10.472(4),b=14.375(2),c=21.695(3)A;α=74.04(1),β=76.50(2),γ=72.22(2)°,V=2950A~3,D_c=1.693g·cm~(-3),Z=2.在CAD-4四圆衍射仪上用MoKα射线收集到I≥2σ(Ⅰ)的衍射点4840个。采用重原子法和差电子密度法解出结构,并用全矩阵最小二乘法修正,最终偏离因子为0.058。簇分子的Mo-Mo键为2.731(1),2.748(1),2.753(1)A,Mo原子和三苯基膦的P原子配位键长为Mo-P2.647(3)A,显著长于一般的Mo-P共价单键。三苯基膦基团在Mo的配位多面体中处于三重桥S原子的对位,表现出与其他此类簇合物的松散配位体配位位置不同。文中概括了此类簇合物的Mo—Mo键和Mo-L的成键情况。     

Binding energy of large icosahedral and cuboctahedral Lennard-Jones clusters

It is widely believed that the lowest energy configurations for small rare gas clusters have icosahedral symmetry. This contrasts with the bulk crystal structures which have cuboctahedral fcc symmetry. It is of interest to understand the transition between this finite and bulk behavior. To model this transition in rare gas clusters we have undertaken optimization studies within the Lennard-Jones pair potential model. Using a combination of Monte Carlo and Partan Search optimization methods, the lowest energy relaxed structures of Lennard-Jones clusters having icosahedral and cuboctahedral symmetry were found. Studies were performed for complete shell clusters ranging in size from one shell having 13 atoms to 14 shells having 10,179 atoms. It was found that the icosahedral structures are lower in energy than the cuboctahedral structures for cluster sizes having 13 shells or fewer. Additional studies were performed using the more accurate Aziz-Chen [HFD-C] pair potential parameterized for argon. The conclusions appear to be relatively insensitive to the form of the potential.     

Structural and energetic properties of Ni-Cu bimetallic clusters

The lowest-energy structures for all compositions of Ni n Cu m bimetallic clusters with N = n + m up to 20 atoms, N = 23, and N = 38 atoms have been determined using a genetic algorithm for unbiased structure optimization in combination with an embedded-atom method for the calculation of the total energy for a given structure. Comparing bimetallic clusters with homoatomic clusters of the same size, it is shown that the most stable structures for each cluster size are composed entirely of Ni atoms. Among the bimetallic clusters in the size range N = 2-20, the Ni N-1 Cu 1 clusters possess the highest stability. Further, it has been established that most of the bimetallic cluster structures have geometries similar to those of pure Ni clusters. The size N = 38 presents a special case, as the bimetallic clusters undergo a dramatic structural change with increasing atom fraction of Cu. Moreover, we have identified an icosahedron, a double, and a triple icosahedron with one, two, and three Ni atoms at the centers, respectively, as particularly stable structures. We show that in all global-minimum structures Ni atoms tend to occupy mainly high-coordination inner sites, and we confirm the segregation of Cu on the surface of Ni-Cu bimetallic clusters predicted in previous studies. Finally, it is observed that, in contrast to the bulk, the ground-state structures of the 15-, 16-, and 17-atom bimetallic clusters do not experience a smooth transition between the structures of the pure copper and the pure nickel clusters as a function of the relative number of the two types of atoms. For these sizes, the concentration effect on energy is more important than the geometric one.     

Structural Evolution of Boron Clusters on Ag(111) Surfaces – From Atomic Chains to Triangular Sheets with Hexagonal Holes

Unlike graphene and other 2D materials, borophene is 2D polymorphic with diverse hexagonal holes (HHs)-triangles ratios and the concentrations of HHs are highly substrate dependent. Here, we systematically explored the evolution of boron cluster on Ag(111) surface, B_N@Ag(111) (N=1∼36), to understand the nucleation of 2D boron sheet on metal surface. Our calculation showed that, with the size increasing, the structures of most stable B_N clusters undergo an evolution from compact triangular lattice, such as double-chains or triple-chains, to the ones with mixed triangular-hexagonal lattices. The first single-HH appears at N=12 and the first double-HH appears at N=27. The stability of large B_N clusters with mixed structures is derived from the charge transfer between triangular lattice and the HHs, as well as between the substrates and the B_N clusters. Our results provide a deep understanding on the formation of small boron clusters in the initial nucleation stage of borophene growth.     

Thermodynamic equilibrium compositions, structures, and reaction energies of Pt(x)O(y) (x = 1-3) clusters predicted from first principles

As synthetic nanocatalysis strives to create and apply well-defined catalytic centers containing as few as a handful of active metal atoms, it becomes particularly important to understand the structures, compositions, and reactivity of small metal clusters as a function of size and chemical environment. As a part of our effort to better understand the oxidation chemistry of Pt clusters, we present here a comprehensive set of density functional theory simulations combined with thermodynamic modeling that allow us to map out the T-p(O)2 phase diagrams and predict the oxygen affinity of Pt(x)O(y) clusters, x = 1-3. We find that the Pt clusters have a much stronger tendency to form oxides than does the bulk metal, that these oxides persist over a wide range of oxygen chemical potentials, and that the most stable cluster stoichiometry varies with size and may differ from the stoichiometry of the stable bulk oxide in the same environment. Further, the facility with which the clusters are reduced depends both on size and on composition. These models provide a systematic framework for understanding the compositions and energies of redox reactions of discrete metal clusters of interest in supported and gas-phase nanocatalysis.     

Configuration of the surface atoms in AlN (270 ≤ N ≤ 500) clusters

Configuration of the surface atoms in aluminum clusters was investigated based on the structures with global minimum potential energy of some Al clusters in the size range of 270-500. The structures were optimized by the dynamic lattice searching with constructed cores (DLSc) method with the NP-B potential. In the optimized structures, all clusters are identified as truncated octahedra (TO) including three complete TO at Al(260), Al(314), and Al(405). With the model of TO(260) and TO(405), the configurations of the surface atoms in the structures of the clusters from 261 to 314 and from 406 to 459 were investigated. The sites on (100) faces are found to be preferable to those on (111) faces for locating the new atoms with the increase of the cluster size, but for the clusters larger than 405 atoms, the sites on the (111) face are favored when the number of atoms exceeds the site number of a (100) face. Furthermore, the sites on the edge adjoining a (100) face and a (111) face are found to be very important to make a cluster more stable.     

Density Functional Theory Study of Structure and Electronic Properties ofMgBen (n=2-12) Clusters

Determinations of the lowest energy structures and electronic properties of MgBen (n=2-12) clusters werecarried out by using density-functional theory. It was found that MgBe3 and MgBe9 clusters with higherbinding energy and larger HOMO-LUMO gap are more stable than the neighboring clusters. The electronicproperties from van der Waals to covalent and bulk metallic behavior in MgBen (n=2-12) clusters arediscussed with the evolution of the size, and the data indicates Magnesium-doped Beryllium clusters alreadyearly appear some metallic-like features than host Ben clusters. By analyzing electronic properties of MgBen(n=2-12) clusters, it can be concluded that Mg-doped reduces the stabilities of Be clusters.     

Clusters of hydrated methane sulfonic acid CH3SO3H.(H2O)n (n = 1-5): a theoretical study

Ab initio and density functional methods have been used to examine the structures and energetics of the hydrated clusters of methane sulfonic acid (MSA), CH3SO3H.(H2O)n (n = 1-5). For small clusters with one or two water molecules, the most stable clusters have strong cyclic hydrogen bonds between the proton of OH group in MSA and the water molecules. With three or more water molecules, the proton transfer from MSA to water becomes possible, forming ion-pair structures between CH3SO3- and H3O+ moieties. For MSA.(H2O)3, the energy difference between the most stable ion pair and neutral structures are less than 1 kJ/mol, thus coexistence of neutral and ion-pair isomers are expected. For larger clusters with four and five water molecules, the ion-pair isomers are more stable (>10 kJ/mol) than the neutral ones; thus, proton transfer takes place. The ion-pair clusters can have direct hydrogen bond between CH3SO3- and H3O+ or indirect one through water molecule. For MSA.(H2O)5, the energy difference between ion pairs with direct and indirect hydrogen bonds are less than 1 kJ/mol; namely, the charge separation and acid ionization is energetically possible. The calculated IR spectra of stable isomers of MSA.(H2O)n clusters clearly demonstrate the significant red shift of OH stretching of MSA and hydrogen-bonded OH stretching of water molecules as the size of cluster increases.     

A G3 study of the structure of carbon-nitrogen nanoclusters

Possible structures of the carbon-nitrogen clusters of the form C(m)N(n) (m = 1-4, n = 1-4, m + n = 2-5) were predicted for the neutral, anion, and cation species in the singlet, doublet, and triplet states, whenever appropriate. The calculations were performed at the G3, MP2(fc)/6-311+G*, and B3LYP/6-311+G* levels of theory. Several molecular properties related to the experimental data--such as the electronic energy, equilibrium geometry, binding energy, HOMO-LUMO gap (HLG), and spin contamination --were calculated. In addition the vertical electron attachment, the adiabatic electron affinity, and vertical ionization energy, of the neutral clusters were calculated. Most of the predicted lowest energy structures were linear, whereas bent structures became more stable with the increase of the cluster size and increase of the number of the N atoms. In most of the predicted lowest energy structures, the N atom prefers the terminal position with acetylenic bond. The calculated BE of the predicted clusters increases with the increase of the cluster size for the neutral and cation clusters but decreases with the increase of the cluster size for the anion clusters. The predicted clusters are characterized by high HLG of about 11 eV on the average, with that of the anion clusters is smaller than that for the neutral and cation clusters. It is concluded then that the anion clusters are less stable than the corresponding neutral and cation clusters. Finally, the N(2) loss reaction is treated.     

Evolution of the properties of Al(n)N(n) clusters with size

A global optimization of stoichiometric (AlN)(n) clusters (n = 1-25, 30, 35, ..., 95, 100) has been performed using the basin-hopping (BH) method and describing the interactions with simple and yet realistic interatomic potentials. The results for the smaller isomers agree with those of previous electronic structure calculations, thus validating the present scheme. The lowest-energy isomers found can be classified in three different categories according to their structural motifs: (i) small clusters (n = 2-5), with planar ring structures and 2-fold coordination, (ii) medium clusters (n = 6-40), where a competition between stacked rings and globular-like empty cages exists, and (iii) large clusters (n > 40), large enough to mix different elements of the previous stage. All the atoms in small and medium-sized clusters are in the surface, while large clusters start to display interior atoms. Large clusters display a competition between tetrahedral and octahedral-like features: the former lead to a lower energy interior in the cluster, while the latter allow for surface terminations with a lower energy. All of the properties studied present different regimes according to the above classification. It is of particular interest that the local properties of the interior atoms do converge to the bulk limit. The isomers with n = 6 and 12 are specially stable with respect to the gain or loss of AlN molecules.