TDDFT studies of electronic structure and first hyperpolarizability of terta-nuclear cubane-like transition metal clusters

The TDDFT method is first applied in a series of tetra-nuclear transition metal clusters studies for nonlinear optical properties. The results indicate that the charge transfer inside the metal core [MCu3X4] (M=W, Mo; X=S, O, Cl, Se, Br) makes contribution to the optical nonlinearity. It is possible to enhance the hyperpolarizability by substituting the ligands of the clusters.     

Fragmentation channels of large multicharged clusters

We address unifying features of fragmentation channels driven by long-range Coulomb or pseudo-Coulomb forces in clusters, nuclei, droplets, and optical molasses. We studied the energetics, fragmentation patterns, and dynamics of multicharged (A+)n (n=55, 135, 321) clusters. In Morse clusters the variation of the range of the pair-potential induced changes in the cluster surface energy and in the fissibility parameter X=E(Coulomb)2E(surface). X was varied in the range of X=1-8 for short-range interactions and of X=0.1-1.0 for long-range interactions. Metastable cluster configurations were prepared by vertical ionization of the neutral clusters and by subsequent structural equilibration. The energetics of these metastable ionic clusters was described in terms of the liquid drop model, with the coefficients of the volume and surface energies depending linearly on the Morse band dissociation energy. Molecular-dynamics simulations established two distinct fragmentation patterns of multicharged clusters that involve cluster fission into a small number of large, multicharged clusters for X<1 and Coulomb explosion into a large number of individual ions and small ionic fragments for X>1. The Rayleigh instability limit X=1 separates between spatially anisotropic fission and spatially isotropic Coulomb explosion. Distinct features of the fragmentation energetics and dynamics were unveiled. For fission of n=55 clusters, large kinetic and internal energies of the large fragments are exhibited and the characteristic fragmentation time is approximately 700 fs, while for Coulomb explosion the major energy content of the small fragments involves kinetic energy and the characteristic fragmentation time of approximately 300 fs is shorter. The Rayleigh (X=1) limit, leading to isotropic Coulomb explosion, is transcended by a marked enhancement of the Coulomb energy, which is realized for extremely ionized clusters in ultraintense laser fields, or by a dramatic reduction of the surface energy as is the case for the expansion of optical molasses.     

Chemical bonding and aromaticity in trinuclear transition-metal halide clusters

Trinuclear transition-metal complexes such as Re(3)X(9) (X = Cl, Br, I), with their uniquely featured structure among metal halides, have posed intriguing questions related to multicenter electron delocalization for several decades. Here we report a comprehensive study of the technetium halide clusters [Tc(3)(μ-X)(3)X(6)](0/1-/2-) (X = F, Cl, Br, I), isomorphous with their rhenium congeners, predicted from density functional theory calculations. The chemical bonding and aromaticity in these clusters are analyzed using the recently developed adaptive natural density partitioning method, which indicates that only [Tc(3)X(9)](2-) clusters exhibit aromatic character, stemming from a d-orbital-based π bond delocalized over the three metal centers. We also show that standard methods founded on the nucleus-independent chemical shift concept incorrectly predict the neutral Tc(3)X(9) clusters to be aromatic.     

First‐principles study of molecular hydrogen dissociation on doped Al12X (X = B,Al, C,Si, P,Mg, and Ca) clusters

Inspired by the concept of superatom via substitutionally doping an Al₁₃ magic cluster, we investigated the H₂ molecule dissociation on the doped icosahedral Al₁₂X (X = B, Al, C, Si, P, Mg, and Ca) clusters by means of density functional theory. The computed reaction energies and activation barriers show that the concept of superatom is still valid for the catalysis behavior of doped metal clusters. The hydrogen dissociation behavior on metal clusters characterized by the activation barrier and reaction energy can be tuned by controllable doping. Thus, doped Al₁₂X clusters might serve as highly efficient and low‐cost catalysts for hydrogen dissociation. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009     

Electron－rich Polynuclear Transition Metal Clusters：Ⅰ． The Clusters with Chalcogen Bridges and Phosphine Ligands

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Regularities of thermal decay of carbonyl chalcogenide metal clusters

The thermal decay of 19 individual carbonyl homo- and heterochalcogenide clusters with different M/X ratios (M = Fe, Mn, Pt, Cr, W, Mo, Re, Ru; X = S, Se, Te) was studied by differential scanning calorimetry and thermogravimetry. The process is stepwise and occurs at relatively low temperatures (100—350 °C). The general fact of incomplete removal of carbon monoxide (due to the formation of carbide and oxide impurities) during thermolysis of narbonyl chalcogenide clusters with the M : X ratio greater than 1 was elucidated. Conversely, when M : X 1 (or at any M/X ratio for clusters containing methylcyclopentadienyl groups), pure metal chalcogenides are formed.     

A comparison of SCF-Xα and extended Hückel methods for metal clusters

A comparison of some results from Xα-scattered wave (Xα-SW) and extended Hückel (EH) calculations for metal clusters is given. It is found that small clusters of atoms (≈ 13 atoms) using the Xα-SW method reproduce many of the features of the electronic structure of the bulk metals, whereas this is not the case for the same clusters using the EH method. A more systematic approach to EH parametrizations is suggested in order to make this method a more viable approach to treating metal clusters.     

Negative ions of transition metal-halogen clusters

A systematic density functional theory based study of the structure and spectroscopic properties of neutral and negatively charged MX(n) clusters formed by a transition metal atom M (M=Sc,Ti,V) and up to seven halogen atoms X (X=F,Cl,Br) has revealed a number of interesting features: (1) Halogen atoms are bound chemically to Sc, Ti, and V for n≤n(max), where the maximal valence n(max) equals to 3, 4, and 5 for Sc, Ti, and V, respectively. For n>n(max), two halogen atoms became dimerized in the neutral species, while dimerization begins at n=5, 6, and 7 for negatively charged clusters containing Sc, Ti, and V. (2) Magnetic moments of the transition metal atoms depend strongly on the number of halogen atoms in a cluster and the cluster charge. (3) The number of halogen atoms that can be attached to a metal atom exceeds the maximal formal valence of the metal atom. (4) The electron affinities of the neutral clusters abruptly rise at n=n(max), reaching values as high as 7 eV. The corresponding anions could be used in the synthesis of new salts, once appropriate counterions are identified.     

DFT,solvation effects,reactivity and SERS analysis on structural,optical, and vibrational properties of a biomolecule of pyrimidine derivative adsorbed on metal clusters of Ag/Au/Cu

Density Functional Theory (DFT) computations were performed to investigate the optical properties of dihydropyrimidine (DHP) and metal clusters of copper (Cu), gold (Au), and silver (Ag). The charge transfers from the metal cluster to DHP through the NH group are revealed by molecular electrostatic potential (MEP) surface and Mulliken charge analysis. Bonding and antibonding orbitals of the DHP-adsorbed metal clusters are responsible for the surface resonance peak in the UV–Vis spectra of DHP adsorbed metal clusters. The polarizability values of DHP-adsorbed on metal clusters are very high in comparison with that of pristine DHP, which suggests an increase in the Non-linear optical (NLO) effect. Our study explores that the DHP adsorbed metal clusters could be used for the NLO materials. The vibrational modes of DHP are enhanced in the DHP adsorbed metal clusters due to surface-enhanced Raman scattering (SERS). Solvation energy is found to be ?21.01, ?29.37, and ?27.82 kcal/mol for DHP-Ag₃/Au₃/Cu₃ which means the DHP-adsorbed metal clusters are stable in thr aqueous medium. The atom in molecule-reduced density gradient (AIM-RDG) isosurface shows weak non-covalent interactions in each DHP adsorbed metal clusters.     

Optical Effects Associated with Aggregates of Clusters

The effect of aggregation on the optical properties of nanometer-sized particles is studied. It is shown that for small noble metal clusters as well as for pigments of Fe₂O₃, TiN, or ZrN, the aggregation leads to changes in the color of the colloidal systems which are caused by electromagnetic coupling among the clusters in the aggregates. The model of interacting particles is shown to be helpful also for interpretation of optical properties of organic dyes with incorporated metal clusters and for interpretation of the reflectance of magnetooptical cluster systems. For soot particles it is shown that scattering and absorption are enhanced over the whole visible spectral region compared to isolated carbonaceous clusters. Finally, it is shown that the model of interacting clusters can also be applied for data interpretation in scanning near-field optical microscopy.     

Anisotropic effects in the optical spectra of magic metal clusters: the role of ionic structure

The effect of the ionic positions on the optical spectra of magic metal clusters is studied via pseudopotential perturbation theory. Electronic many-body effects are considered within perturbed time-dependent local-density-approximation. Quantitative agreement with recent experiments by Reiners et al. is obtained. In this way a natural explanation is obtained for the temperature dependence of the optical absorption of magic metal clusters.     

Structure and photoabsorption properties of cationic alkali dimers solvated in neon clusters

We present a theoretical investigation of the structure and optical absorption of M(2)(+) alkali dimers (M=Li,Na,K) solvated in Ne(n) clusters for n=1 to a few tens Ne atoms. For all these alkali, the lowest-energy isomers are obtained by aggregation of the first Ne atoms at the extremity of the alkali molecule. This particular geometry, common to other M(2)(+)-rare gas clusters, is intimately related to the shape of the electronic density of the X (2)Σ(g)(+) ground state of the bare M(2)(+) molecules. The structure of the first solvation shell presents equilateral Ne(3) and capped pentagonal Ne(6) motifs, which are characteristic of pure rare gas clusters. The size and geometry of the complete solvation shell depend on the alkali and were obtained at n=22 with a D(4h) symmetry for Li and at n=27 with a D(5h) symmetry for Na. For K, our study suggests that the closure of the first solvation shell occurs well beyond n=36. We show that the atomic arrangement of these clusters has a profound influence on their optical absorption spectrum. In particular, the XΣ transition from the X (2)Σ(g)(+) ground state to the first excited (2)Σ(u)(+) state is strongly blueshifted in the Frank-Condon area.     

Surface Study of Supported Metal Catalysts

The aim of the reported studies was to determine the catalytic behaviour of M-C systems (M=Pt, Pd and Ru) towards hydrogenolysis of the C-X bond (X=Cl and F). The level of noble metal loading is reflected in the size of the metal clusters formed on the surface of the carbon support and affects the product distribution and the amount of carbonaceous deposit formed upon the conversion of CCl₂F₂. This revised version was published online in July 2006 with corrections to the Cover Date.     

若干新型结构和新的成键方式的金属羰基簇合物

本文介绍了几位作者所合成并用X射线单晶结构分析表征的五类新型Fe,Co,Ru羰基簇合物。讨论其成键方式与结构特点。并介绍某些具有双键的配位基以不同的断裂方式提供不同的分子片配位于原子簇骨架的情况。     

Template‐Dependent Photochemical Reactivity of Molecular Metal Oxides

A combined experimental and theoretical study shows that the photooxidative activity of two isostructural metal oxide clusters depends on their internal templates. To this end, two halide‐templated bismuth vanadium oxide clusters [X(Bi(dmso)₃)₂V₁₂O₃₃]^? (X=Cl^?, Br^?) are reported and fully characterized. The two clusters show similar absorption features and illustrate that bismuth incorporation results in increased visible‐light absorption. Significantly higher photooxidative activity is observed for the bromide‐templated cluster compared with the chloride‐templated one. Detailed photophysical assays and complementary DFT calculations suggest that the more efficient triplet excited state formation in the Br^?‐containing cluster is the decisive step in the photocatalysis and is due to the heavy‐atom effect of the bromide. This concept can therefore open new pathways towards the optimization of photocatalytic activity in metal oxide clusters.     

含Pt配合物电子结构和非线性光学性质的TDDFT研究

利用含时密度泛函理论(TDDFT)对trans-(PEt3)2Pt(X)(p-Ph-NO2)的有机金属配合物进行结构优化, 并计算了电子光谱和二阶非线性光学(NLO)性质, 结果表明在1064 nm光场下, 2个分子的共振效应很强, 在远离共振的1907nm的下, 分子的一阶超极化率是尿素的40倍左右。     

碱金属原子簇的结构和稳定性

基于从体心立方碱金属晶体优化确立的多体展开势能函数，本文通过坐标优化研究了碱金属原子簇Ｘｎ（Ｘ＝Ｌｉ，Ｎａ，Ｋ，Ｒｂ，Ｃｓ）的结构和稳定性。发现：（１）Ｘｎ原子簇（ｎ＝４－２１）倾向于形成畸变四面体结构单元，（Ｔｄ）的密堆积，分子表面被三元环（Ｄ３ｈ）所覆盖，其中Ｘ７－Ｘ１５最优化结构中包含五角双锥Ｘ７（Ｄ５ｈ）结构单元，具有区域五重对称轴；（２）“微观晶体碎片”的分层优化结果表明，体心立方、面心     

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.     

Structural characterization of the anions [Rh6(CO)15X]− [X = COEt and CO(OMe)]

The anions [Rh₆(CO)₁₅X]^?, with X = COEt and CO(OMe), have been studied by single-crystal X-ray diffraction. They contain octahedral rhodium clusters, with mean metalmetal distances of 2.779 and 2.765 », respectively. The carbonyl stereochemistry in the two anions is similar to that of Rh₆(CO)₁₆, with one terminal CO group replaced by the X ligand. The RhC(carbomethoxy) bond distance (1.96(2) ») is significantly shorter than the RhC(acyl) distance (2.06(2) »).     

簇合物Mo_2X_8~(4-)(X=Cl,Br)低能态电子光谱

应用间略微分重叠自洽场和组态作用(INDO/S-CI)方法,计算双核簇合物Mo_2X_8~(4-)(X=Cl,Br)基态~1A_(1g)至不同低能态的d电子自旋允许的跃迁能,得出Mo—Mo四重键均裂时所需的能量大小依次为键σ>π>>δ。对于Mo_2Cl_8~(4-)簇合物态~1A_(1g)→1~1A_(2u)(δ→δ~*)和~1A_(1g)→2~1E_g(π→δ~*)的电子跃迁能,理论值(15584和22587cm~(-1))与低温时测得光谱实验值(18083和22000cm~(-1))较为接近。此外,本文还提出了簇合物Mo_2X_8~(4-)的态相同而X不同时,电子跃迁能变化,主要决定于参与电子转移过程的分子轨道组成成份的看法。