过渡金属纯簇和混合簇的密度泛函研究:Nb4,Co4和Nb2Co2

用密度泛函方法对过渡金属双原子Nb₂,Co₂和NbCo的电子态进行研究,得到三者的基态分别为³∑_g^-,⁵∑_g⁺和³△.并以此为基础,讨论四核簇Nb₄,Co₄和No₂Co₂的成键情况,发现稳定的单金属簇Nb₄具有高对称性的密堆结构,稳定的Co₄具有低对称性的变形封闭结构,两者都是典型的金属键;而Nb₂Co₂在封闭式结构中是一般的金属键,在线形结构中有强弱交替的定域键,Nb原子易相互靠近成键,Co原子趋于远离不成键.三种团簇的多重度以Nb₄＜Nb₂Co₂＜Co₄顺序依次升高.     

平面五配位硅、 锗XBe5H6(X=Si,Ge)团簇

采用密度泛函理论PBE0方法, 在aug-cc-pVTZ水平上理论预测了含平面五配位硅和锗原子的XBe₅H₆ (X=Si, Ge)团簇. 势能面系统搜索及高精度量化计算表明, 它们均为全局极小结构. XBe₅H₆(X=Si, Ge)团簇整体呈完美的扇形结构: Si/Ge原子被5个金属Be原子配位; 4个H原子以桥基方式与Be原子相键连, 剩余的2个 H原子以端基方式与两端的Be原子成键. 化学键分析表明, XBe₅H₆(X=Si, Ge) 团簇中XBe₅单元具有完全离域的1个π及3个σ键, 外围铍氢间形成4个Be—H—Be 三中心二电子(3c-2e)键及2个定域的Be—H键. XBe₅单元上离域的2π及6σ电子赋予体系π和σ双重芳香性, 并使Si/Ge原子满足八隅律（或八电子规则）. 能量分解-化学价自然轨道分析揭示, Si/Ge和Be₅H₆之间主要为电子共享键.     

单层石墨相氮化碳负载Pt4团簇吸附O2的第一性理论研究

采用第一性原理密度泛函理论结合周期性平板模型模拟研究了Pt₄团簇吸附单层石墨相氮化碳(g-C₃N₄)的几何结构和电子性质,以及氧气在其表面上的吸附行为。同时,对比分析了氧气在纯净的石墨相氮化碳和Pt₄团簇上的吸附行为。计算结果表明, Pt₄团簇吸附在3-s-三嗪环石墨相氮化碳表面,并与四个边缘氮原子成键,形成两个六元环时为最稳定构型。Pt₄团簇倾向于吸附在三嗪环石墨相氮化碳的空位并与邻近三个氮原子成键。由于Pt与N原子较强的杂化作用,以及金属与底物之间较多电子转移增强了Pt₄团簇吸附g-C₃N₄的稳定性。另外,对比分析了氧气在纯净的g-C₃N₄和金属吸附的g-C₃N₄上吸附行为,发现金属原子的加入促进了电子转移,同时拉长了O―O键长。Pt₄吸附3-s-三嗪环g-C₃N₄比Pt₄吸附三嗪环g-C₃N₄表现出微弱的优势,表现出明显的基底扭曲以及较大的吸附能。这些结果表明,化学吸附通过调节电子结构和表面性质增强催化性能的较好方法。     

八电子Pd4四面体团簇的电子结构稳定性分析

基于理论计算,我们报道了T_d对称性的[Pd₄(μ₃-SbH₃)₄(SbH₃)₄]团簇及一系列类似物的结构与成键。成键分析表明：每个Pd原子都是sp³杂化,其10个价电子与四个配体提供的8个价电子,满足18电子规则。并且,每个Pd原子与四个桥连的SbH₃配体可以形成四个离域的四中心两电子超级σ键或八中心两电子键。一方面,根据超原子网络模型,这个钯团簇可以描述成四个2电子的超原子网络。另一方面,凝胶模型表明,它可以合理化的作为电子组态是1S²1P⁶的8电子超原子。与此同时,d¹⁰…d¹⁰闭壳层相互作用在稳定Pd₄四面体结构中起到了关键性的作用。密度泛函理论计算表明：T_d对称性[Pd₄(μ₃-SbH₃)₄(SbH₃)₄]团簇表现出高度稳定性,具有充满的电子壳层,大的HOMO-LUMO带隙(2.84 eV)以及负的核独立化学位移(NICS)值。此外,基于[Pd₄(μ₃-SbH₃)₄(SbH₃)₄]结构与成键模式,我们设计了一系列稳定的类似物,其有可能被实验合成出来。     

碱土金属叠氮化合物(CaN6)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(CaN₆)_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, CaN₆团簇的最稳定结构为线型结构, (CaN₆)_n (n＝2～5)团簇首先由两个叠氮基与两个Ca原子构成一个近似菱形, 再由菱形相互垂直形成链状最稳定结构; 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Ca直接作用的N原子负电性更强, 金属Ca原子和N原子之间形成很强的离子键; (CaN₆)_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2195～2280 cm^－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, (CaN₆)₃和(CaN₆)₅团簇相对于其他团簇较为稳定.     

硫醇保护金团簇的实验和理论研究现状

硫醇保护的金团簇(Au_m(SR)_n,m和n为Au和SR的数目)由于其特殊的光学、电学性质以及特别的物理/化学性质,在纳米催化、生物医学和光学设备中具有潜在的应用价值。Au₁₀₂(SR)₅₄和Au₂₅(SR)₁₈^-团簇单晶结构的确定是Au_m(SR)_n团簇合成的两大突破,它们的结构揭示了Au_m(SR)_n团簇中Au-S键新的成键特征和新的原子堆积方式。本文总结了Au_m(SR)_n团簇实验合成单晶结构的研究成果,概述了有谱图无单晶结构的Au_m(SR)_n团簇的实验进展,介绍了密度泛函理论预测Au_m(SR)_n团簇的研究概况,并结合本课题组的研究课题归纳了解释团簇稳定性和化学成键方式的超原子复合物模型,超原子网络模型和超级共价键模型及其应用。最后,对Au_m(SR)_n团簇的研究趋势进行了展望。     

(HCaN3)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*水平上对叠氮化合物(HCaN₃)_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, HCaN₃团簇最稳定结构为折线型, (HCaN₃)_n (n＝2～4)团簇最稳定结构为叠氮基端位N原子与Ca原子相互链接形成平面环状结构, (HCaN₃)₅团簇最稳定结构为立体钟形结构. 团簇最稳定结构中金属Ca原子均显示正电性, H原子均显示负电性, 叠氮基中间的N原子显示正电性, 叠氮基两端的N原子显示负电性, 且和Ca原子直接作用的N原子的负电性更强. Ca-N键和Ca-H键为典型的离子键, 叠氮基内N原子之间是共价键. 最稳定结构的IR光谱主要分为3个部分, 其最强振动峰均位于2193～2302 cm^－1段, 振动模式为叠氮基中N-N键的反对称伸缩振动. 叠氮基在团簇和晶体中结构不变, 始终以直线型存在, 说明金属叠氮化合物团簇可以很好地模拟其晶体的局域成键和局域电荷转移等特性. 稳定性分析显示, (HCaN₃)₃团簇相对于其他团簇更稳定.     

六核簇离子Te64+和P64-的电子结构与化学键

本文用EHMO法计算六核簇离子Te₆⁴⁺和P₆^4-的电子结构。分析与它们相同构型的棱柱烷C₆H₆和苯在成键性质上的差异。结果表明,这两簇离子的多余价电子填充到能级略高于自由原子p轨道的弱反键分子轨道。     

二核铌钼硫簇NbMoS_n~(-/0)(n=3～7)掺杂体系的结构与成键性质的理论研究

近年来,过渡金属硫化物作为催化材料在许多化学反应中扮演着重要角色,特别是在石油化工领域的加氢脱硫与加氢脱氮等环节中被广泛应用.本工作采用密度泛函理论结合高精度的耦合簇[CCSD(T)]计算方法,对掺杂类型的铌钼硫簇NbMoS_n~(-/0)(n=3~7)进行系统研究,确定其最稳定的几何结构,并探讨掺杂、调节硫含量、改变团簇所带电荷等手段,对掺杂类型铌钼硫簇几何构型、电子结构与化学成键等性质的影响.本工作采用广义Koopmans定理计算NbMoS_n~-(n=3~7)阴离子基态的电子垂直逸出能(VDEs),模拟相应的阴离子光电子能谱图(PES),并结合对分子轨道的分析来进一步阐述该体系在几何结构与化学成键等性质上的演变规律.本工作可为进一步开展铌钼硫簇掺杂体系的理论与实验研究提供较为可靠的理论依据.     

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.     

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.     

Density-functional study of small neutral and cationic bismuth clusters Bi(n) and Bi(n) (+)(n=2-24)

Density-functional theory with scalar-relativistic pseudopotential and a generalized gradient correction is used to calculate the neutral and cationic Bi(n) clusters (2< or =n< or =24), with the aim to elucidate their structural evolution, relative stability, and magnetic property. The structures of neutral Bi clusters are found to be similar to that of other group-V elemental clusters, with the extensively studied sizes of n=4 and 8 having a tetrahedron and wedgelike structure, respectively. Generally, larger Bi clusters consist of a combination of several stable units of Bi(4), Bi(6), and Bi(8), and they have a tendency to form an amorphous structure with the increase of cluster sizes. The curves of second order energy difference exhibit strong odd-even alternations for both neutral and cationic Bi clusters, indicating that even-atom (odd-atom) sizes are relatively stable in neutral clusters (cationic clusters). The calculated magnetic moments are 1micro (B) for odd-atom clusters and zero for even-atom clusters. We propose that the difference in magnetism between experiment and theory can be greatly improved by considering the orbital contribution. The calculated fragmentation behavior agrees well with the experiment, and for each cationic cluster the dissociation into Bi(4) or Bi(7) (+) subclusters confirms the special stability of Bi(4) and Bi(7) (+). Moreover, the bond orders and the gaps between the highest occupied molecular orbital and the lowest unoccupied molecular orbital show that small Bi clusters would prefer semiconductor characters to metallicity.     

Pb_mTe_n(m+n≤6)团簇的结构与稳定性(英文)

采用密度泛函理论(DFT)的B3LYP方法,在SDD基组水平上对PbmTen(m+n≤6)团簇的几何结构、平均原子键能、离解能及HOMO-LUMO能隙进行了计算分析.结果表明:纯Pb团簇比纯Te团簇稳定,PbnTe比PbTen(n=2-5)稳定,PbnTe2比Pb2Ten(n=3-4)更加稳定;混合团簇PbmTen的HOMO-LUMO能隙在1.87-3.55eV之间,表明该团簇具有半导体性质;在所有团簇中,PbTe团簇最稳定.     

Ionic dissociations of chlorosulfonic acid in microsolvated clusters: A density functional theory and ab initio MO study

Ionic dissociation of chlorosulfonic acid (HSO3Cl) in the molecular clusters HSO3Cl-(H2O)n (n = 1-4) and HSO3Cl-NH3-(H2O)n (n = 0-3) was investigated by density functional theory and ab initio molecular orbital theory. The equilibrium structures, binding energies, and thermodynamic properties, such as relative enthalpy and relative Gibbs free energy, and were calculated using the hybrid density func- tional (B3LYP) method and the second order M?ller-Plesset approximation (MP2) method with the 6-311 G** basis set. Chlorosulfonic acid was found to require a minimum of three water molecules for ionization to occur and at least one water molecule to protonate ammonia. The corresponding clusters with fewer water molecules were found to be strongly hydrogen-bonded. The related properties and acid strength of chlorosulfonic acid were discussed and compared to the acid strengths of perchloric acid and sulfuric acid in the context of clusters with ammonia and water. The relative stabilities of these clusters were also investigated.     

Fe_(6-x)Al_x团簇的结构和磁性能

在密度泛函理论的BPW91水平上,对Fe6-xAlx团簇进行了结构优化,并将获得的最低能结构进行稳定性分析以及电子结构和磁性能的计算.计算结果表明,铁原子倾向团聚在一起并占据最高配位,Al原子则倾向分布在铁簇的周围尽最大可能地与Fe配位成键.Fe6-xAlx团簇的磁性随Al原子数目增加呈现下降趋势,自然轨道分析揭示Fe4s和Al3s与Fe3d之间的杂化是导致团簇磁矩下降的主要原因.     

Optical and Electrical Properties of Triphenylamine Derivatives for Dye-sensitized Solar Cells and Designing of Novel Molecule

With density functional theory(DFT) method, the optimization of molecular configurations and the calculation of frontier molecular orbitals were achieved for triphenylamine(TPA)-based dye-sensitized solar cell materials at the B3LYP/6-31G(d, p) level. Time-dependent density functional theory(TD-DFT) was applied to calculating the probability of the transition from the ground state to the excited state. And UV-Vis absorption spectra were derived with Franck-Condon approximation. The conjugation length, substitution groups and spatial effects show a slight influence on the dihedral angle of the TPA group. The increase of conjugation length may cause a smaller energy gap as well as a higher highest occupied molecular orbital(HOMO) and a lower lowest unoccupied molecular orbital (LUMO). The introduction of methoxyl group and TPA group could lower the energy gap while the HOMO and LUMO were elevated in energy.     

PDECO: Parallel differential evolution for clusters optimization

The optimization of the atomic and molecular clusters with a large number of atoms is a very challenging topic. This article proposes a parallel differential evolution (DE) optimization scheme for large‐scale clusters. It combines a modified DE algorithm with improved genetic operators and a parallel strategy with a migration operator to address the problems of numerous local optima and large computational demanding. Results of Lennard–Jones (LJ) clusters and Gupta‐potential Co clusters show the performance of the algorithm surpasses those in previous researches in terms of successful rate, convergent speed, and global searching ability. The overall performance for large or challenging LJ clusters is enhanced significantly. The average number of local minimizations per hit of the global minima for Co clusters is only about 3–4% of that in previous methods. Some global optima for Co are also updated. We then apply the algorithm to optimize the Pt clusters with Gupta potential from the size 3 to 130 and analyze their electronic properties by density functional theory calculation. The clusters with 13, 38, 54, 75, 108, and 125 atoms are extremely stable and can be taken as the magic numbers for Pt systems. It is interesting that the more stable structures, especially magic‐number ones, tend to have a larger energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital. It is also found that the clusters are gradually close to the metal bulk from the size N > 80 and Pt₃₈ is expected to be more active than Pt₇₅ in catalytic reaction. © 2013 Wiley Periodicals, Inc.     

AlnO2±团簇结构的几何特征与稳定性

采用密度泛函理论(DFT)的B3LYP方法,在6-311G**水平上对AlnO2±(n=1-10)团簇的几何和电子结构进行了理论计算.讨论了混合团簇的基态结构与振动频率,以及电荷转移与分子轨道.结果表明,AlnO2±(n>1)团簇的基态结构都是2个较小的AlmO(m相似文献   

InAs管状团簇及单壁InAs纳米管的结构、稳定性和电子性质

采用密度泛函理论研究了InnAsn (n≤90)管状团簇以及单壁InAs纳米管的几何结构、稳定性和电子性质. 小团簇InnAsn (n=1-3)基态结构和电子性质的计算结果与已有报道相一致. 当n≥4时优化得到了一族稳定的管状团簇, 其结构基元(In原子与As原子交替排列的四元环和六元环结构)满足共同的衍化通式. 团簇的平均结合能表明横截面为八个原子的管状团簇稳定性最好. 管状团簇前线轨道随尺寸的变化规律有效地解释了一维稳定管状团簇的生长原因, 同时也说明了实验上之所以能合成InAs纳米管的微观机理. 此外, 研究结果表明通过管状团簇的有效组装可得到宽带隙的InAs半导体单壁纳米管.     

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.