(AB)8(AB=BN，AlP，GaAs，InSb)团簇环状结构与性质的密度泛函理论研究

用杂化密度泛函B3LYP方法研究了(AB)₈(AB=BN，AlP，GaAs，InSb)团簇环形结构的平衡几何构型、电子结构、振动特性以及极化率。计算结果表明，(AB)₈团簇的双层环状结构中，每个A(B)原子都与3个B(A)原子成键，且Ⅴ族元素的原子比Ⅲ族元素的原子更接近团簇中心，(BN)₈、(AlP)₈、(GaAs)₈、(InSb)₈的平均极化率依次增大，IR和Raman谱峰发生红移。另外，讨论了热力学稳定性和动力学稳定性的变化。     

(BN)n(n≤12)团簇的结构及成键性质

利用遗传算法和Gastreich提出的经验势函数研究了(BN)_n(n≤12)团簇的可能稳定结构, 并对能量较低的异构体在HF/6-31G(d)水平进行优化, 得到了(BN)_n(n≤12)团簇的线状、蒲扇形、单环、双环、三环和笼状结构, 讨论了各种结构的特征及相对稳定性. 分析了BN团簇中原子的成键性质, 在单环结构中, N原子以sp2杂化成键, B原子以sp杂化成键, 而在节点处B原子以sp2杂化成键. (BN)6是唯一没有张力的单环结构.     

第一原理对AlPm和AlPm-(m = 2～9)团簇结构与稳定性的研究

用密度泛函理论(DFT)的B3LYP方法,在6-311G*水平上对AlPm和AlPm(m = 2～9)团簇的几何构型,电子结构和振动频率等性质进行了理论研究,给出了一种以Pm团簇作为设计AlPm类结构的母体,考虑在不同位置上结合Al原子的结构,可以较快找到AlPm类团簇基态结构的方法. 通过对基态结构的第一离解能和能量二次差分讨论,得到m为奇数的AlPm团簇比m为偶数的稳定,对基态结构的HOMO-LUMO能隙和绝热电子亲合势的讨论表明,AlP3,AlP5和AlP7团簇结构较稳定.     

(BN)_n团簇的结构和稳定性

用HF方法、密度泛函理论的B3LYP以及微扰理论的MP2方法 ,在 6 3 1G(d)基组水平上 ,对 (BN) n(n =1～ 16)团簇的各种可能结构进行了优化 .讨论了环状与笼状稳定团簇的几何构型、自然键轨道 (NBO)、振动频率、结合能、核独立化学位移 (NICS)和能量二次差分 ,得到了 (BN) n(n =1～ 16)团簇结构的稳定性信息 .比较了HF ,B3LYP以及MP2三种理论方法对(BN) n 团簇的适应性所表现出的差异 .     

(BN)n团簇的结构和稳定性

用HF方法、密度泛函理论的B3LYP以及微扰理论的MP2方法，在6—31G(d)基组 水平上，对(BN)n(n=1-16)团簇的各种可能结构进行了优化．讨论了环状与笼状稳 定团簇的几何构型、自然键轨道(NBO）、振动频率、结合能、核独立化学位移 (NICS)和能量二次差分，得到了(BN)n(n＝1-16)团簇结构的稳定性信息．比较了 HF，B3LYP以及MP2三种理论方法对(BN)n团簇的适应性所表现出的差异．     

碱土金属叠氮化合物(MgN_6)_n(n=1～5)团簇结构与性质的密度泛函理论研究

利用密度泛函理论在B3LYP/6-311G*水平上对碱土金属叠氮化合物(MgN6)n(n=1～5)团簇各种可能构型进行了几何优化,预测了各团簇的最稳定结构。并对最稳定结构的成键特性、电荷分布、振动特性及稳定性进行理论研究。结果表明,叠氮化合物中叠氮基以直线型存在,MgN6团簇最稳定结构为直线型;(MgN6)2团簇最稳定结构为Mg2N2四元环平面结构;(MgN6)n(n=3～5)团簇最稳定结构是由2个叠氮基与2个Mg原子首先构成近似菱形,再由近似菱形延伸形成的链状结构。叠氮基中间的N原子显示正电性,两端的N原子显示负电性,且与Mg直接作用的N原子负电性更强,金属Mg原子和N原子之间形成很强的离子键。(MgN6)n(n=1～5)团簇最稳定结构的IR光谱分为4个部分,其最强振动峰均位于2209～2313cm-1,振动模式为叠氮基中N-N键的反对称伸缩振动。稳定性分析显示,(MgN6)3和(MgN6)5团簇相对于其他团簇较为稳定。     

Pdn(n=2～13)团簇的密度泛函理论研究

采用密度泛函理论B3LYP方法计算并讨论钯原子团簇Pdn(n=2～13)结构模型.通过对钯原子团簇进行几何构型优化和振动频率计算,找出团簇总能量最低的同分异构体.由于Jahn-Teller效应的存在,团簇的最稳定结构采取对称性较低的几何构型.在钯原子数相同时,往往存在多个能量极为相近的稳定构型.单位原子平均静态极化率呈奇偶变化.     

(XY)12(X=B,Al;Y=P)团簇的结构与稳定性

采用B3LYP／6031G*方法,对(XY)12(X=B,Al;Y=P)笼状团簇的同分异构体进行优化,筛选出能量最低的构型．讨论它们的几何构型、HOMO-LUMO能隙、生成焓、核独立化学位移(NICS)和自由能．得到(BP)12和(AlP)12团簇的最稳定构型均为具有Th对称性的四、六元环组成的笼,亚稳态结构中含有五元环。     

(Mg3N2)n(n=1～4)团簇结构与性质的密度泛函研究

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(Mg3N2)n(n=1～4)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、电荷特性和稳定性等进行了理论分析.结果表明:(Mg3N2)n=1～4团簇易形成笼状结构,其最稳定构型中N原子配位数以3、4较多见;团簇主要由Mg-N键组成,Mg-N键长为0.194～0.218nm,Mg-Mg 键长为0.262～0.298 nm;N原子的平均自然电荷为-2.06 e,Mg原子的平均自然电荷为 1.37 e;(Mg3N2)2团簇有相对较高的动力学稳定性.     

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.     

The structure and energetics of (GaAs)n, (GaAs)n(-), and (GaAs)n+ (n=2-15)

Electronic and geometrical structures of neutral, negatively, and positively charged (GaAs)n clusters are computed using density functional theory with generalized gradient approximation. All-electron computations are performed on (GaAs)2-(GaAs)9 while effective core potentials (ECPs) are used for (GaAs)9-(GaAs)15. Calibration calculations on GaAs and (GaAs)9 species support the use of the ECP for the larger clusters. The ground-state geometries of (GaAs)n(-) and/or (GaAs)n+ are different from the corresponding neutral ground-state geometry, except for n=7, 9, 12, 14, and 15, where the neutral and ions have similar structures. Beginning with n=6, all atoms are three coordinate, except for (GaAs)10+ and (GaAs)13+. For the larger species, there is a competition between fullerenes built from hexagons and rhombi and geometrical configurations where Ga-Ga and As-As bonds are formed, which results in the formation of pentagons. As expected, the static polarizability varies in the order of anion>neutral>cation, but the values are rather similar for all three charge states. The thermodynamic stability for the loss of GaAs is reported.     

Computational studies of small (AlP)N clusters

We have carried out extensive LDA calculations to investigate the structures of small (AlP)_N clusters.We find that the polarity of the Al-P bond has a significant effect on the cluster geometries and that the need to minimize electrostatic repulsion between relatively diffuse lone pair electrons on phosphorous atoms is a dominant energetic consideration in the structural arrangement.     

Experimental and computational study of small (N = 1-16) stoichiometric zinc and cadmium chalcogenide clusters

Zinc selenide, cadmium sulfide, and cadmium selenide clusters were produced by direct laser ablation and analyzed in a time-of-flight mass spectrometer. The positive-ion mass spectra indicated that clusters composed of six and thirteen monomer units were ultrastable in all cases. The geometries and energies of the neutral and positively charged M(n)X(n) clusters up to n = 16 were obtained computationally at the B3LYP level of theory using the SKBJ basis set for the metal atoms and the SKBJ(d,2df) basis set for the chalcogen atoms. Small neutral and positive clusters (n = 1-4) have planar geometries, neutral three-dimensional clusters have the geometry of closed-cage polyhedra, and cationic three-dimensional clusters have structures with a pair of two-coordinated atoms. Physical properties of the clusters as a function of size are reported. The relative stability of the positive stoichiometric clusters provides a thermodynamic explanation for the relative stability observed experimentally from the laser-ablation mass spectrometry.     

Experimental and computational study of the Zn(n)S(n) and Zn(n)S(n)+ clusters

Zinc sulfide clusters produced by direct laser ablation and analyzed in a time-of-flight mass-spectrometer, showed evidence that clusters composed of 3, 6, and 13 monomer units were ultrastable. The geometry and energies of neutral and positively charged Zn(n)S(n) clusters, up to n = 16, were obtained computationally at the B3LYP/6-311+G level of theory with the assistance of an algorithm to generate all possible structures having predefined constraints. Small neutral and positive clusters were found to have planar geometries, neutral three-dimensional clusters have the geometry of closed-cage polyhedra, and cationic three-dimensional clusters have structures with a pair of two-coordinated atoms. Physical properties of the clusters as a function of size are reported. The relative stability of the positive stoichiometric clusters provides a thermodynamic rationale for the experimental results.     

Geometries, stabilities, and electronic properties of different-sized ZrSi(n) (n=1-16) clusters: a density-functional investigation

The ZrSi(n) (n=1-16) clusters with different spin configurations have been systematically investigated by using the density-functional approach. The total energies, equilibrium geometries, growth-pattern mechanisms, natural population analysis, etc., are discussed. The equilibrium structures of different-sized ZrSi(n) clusters can be determined by two evolution patterns. Theoretical results indicate that the most stable ZrSi(n) (n=1-7) geometries, except ZrSi3, keep the analogous frameworks as the lowest-energy or the second lowest-energy Si(n+1) clusters. However, for large ZrSi(n) (n=8-16) clusters, Zr atom obviously disturbs the framework of silicon clusters, and the localized position of the transition-metal (TM) Zr atom gradually varies from the surface insertion site to the concave site of the open silicon cage and to the encapsulated site of the sealed silicon cage. It should be mentioned that the lowest-energy sandwich-like ZrSi12 geometry is not a sealed structure and appears irregular as compared with other TM@Si12 (TM = Re,Ni). The growth patterns of ZrSi(n) (n=1-16) clusters are concerned showing the Zr-encapsulated structures as the favorable geometries. In addition, the calculated fragmentation energies of the ZrSi(n) (n=1-16) clusters manifest that the magic numbers of stabilities are 6, 8, 10, 14, and 16, and that the fullerene-like ZrSi16 is the most stable structure, which is in good agreement with the calculated atomic binding energies of ZrSi(n) (n=8-16) and with available experimental and theoretical results. Natural population analysis shows that the natural charge population of Zr atom in the most stable ZrSi(n) (n=1-16) structures exactly varies from positive to negative at the critical-sized ZrSi8 cluster; furthermore, the charge distribution around the Zr atom appears clearly covalent in character for the small- or middle-sized clusters and metallic in character for the large-sized clusters. Finally, the properties of frontier orbitals and polarizabilities of ZrSi(n) are also discussed.     

Dipole polarizabilities of germanium clusters

Dipole polarizabilities of Ge_n clusters with 2–25 atoms are calculated using finite field (FF) method within density functional theory. The dipole moments and polarizabilities of clusters are sensitively dependent on the cluster geometries and electronic structures. The clusters with low symmetry and large HOMO–LUMO gap prefer to large dipole moments. The polarizabilities of the Ge_n clusters increase rapidly in the size range of 2–5 atoms and then fluctuate around the bulk value. The larger HOMO–LUMO gap may lead to smaller polarizability. As compared with the compact structure and diamond structure, the prolate cluster structure corresponds to a larger polarizability.