Structure,stability, and vibrational properties of small silver cluster

The ground state geometries and binding energies of small silver clusters were found using Density Functional Theory (DFT) methods. We have compared various non local corrections for exchange and correlation energies, with or without treating explicitely all the electrons. The transferability of standard effective core potentials (ECP) is good, as far as their core size is small enough. From these results, and after comparison with ab initio CI one electron- ECP calculations, we have concluded to the ability of describing small silver clusters as one-electron systems. Thus, we have parametrized our distance-dependent tight- binding hamiltonian (DDTB), previously applied to alkali clusters. The geometries and energies provided by the model are very close to those found in ab initio calculations when available, that is, up to Ag₉. We have also computed the harmonic frequencies of small silver clusters.     

Ru_n(n=2~8)金属团簇的结构和能级分布的DFT研究

采用密度泛函理论中的广义梯度近似(DFT/GGA)方法,对Run团簇(n = 2~8)的几何结构与稳定性、束缚能以及能级分布的关系进行了研究,并分析了随着团簇原子数的增加,团簇的几何结构和费米能级的变化,结果表明:Ru簇的几何结构在4个原子以前是平面结构,而从5个原子开始为空间立体的稳定结构,束缚能随金属原子数的增加而增加。能级结构呈明显的分立特征,费米能级随原子个数的增加而增加,但从Ru7开始又有所降低,且团簇的能量间隙逐渐减小,趋近于大块金属的能级特征。     

Density Functional Calculation of the Photoelectron Emission Spectra of BiSCl Crystal and Molecular Clusters

The photoelectron emission spectra of BiSCl crystal and molecular clusters have been calculated by the Density Functional Theory (DFT) method. Molecular clusters consists from 2 to 20 molecules in one double chain along z(c) axis. Total and partial density of states of BiSCl crystal and clusters have been weighted with atomic photoemission emission cross-section. The molecular clusters have been investigated including all normal modes of vibration. Theoretical results of BiSCl crystal and molecular clusters have been compared with experimental X-ray photoelectron emission spectra (XPS) of BiSI crystal.     

Syntheses and spectroscopic properties of substituted diazaborepins with large stokes shift

The substituted diazaborepins (DABs) with halogen (Cl, Br), methoxyl and ethyl ester group on the fifth position of indole unit have large stokes shift, high fluorescence quantum yields and would be used in biomedicine. Their absorption and emission properties were studied in different solvents. Electron-withdrawing group tended to a bathochromic shift of the absorption and fluorescence probably due to its D-π-A structure. Solvatochromic effects were also studied based on Lippert-Mataga equation. DAB-5 with ethyl ester group exhibits more pronounced fluorescence solvatochromic effects than DAB-3 with Br group. The energy gap and simulated stick spectra of DABs based on Density Functional Theory (DFT) and Time-dependent Density Functional Theory (TD-DFT) calculation was obtained.     

Structural and dynamical properties of magnesium microclusters

We present systematic Density Functional Theory-Local Density Approximation computations for neutral Magnesium clusters Mg _n withn≤13. For the smaller sizes the ground state structure is optimized starting from selected symmetries and allowing for relaxation, Jahn-Teller distorsion and spin polarization. For the larger sizes we perform a simulated annealing based on the ab-initio Molecular Dynamics. By the same method, we study the thermal and dynamical properties of Mg₁₀ and Mg₁₆. The general picture emerging from these computations shows that already atn ≈10 these clusters have acquired many characteristic features of metallic Magnesium.     

The Structural and Electronic Properties of Tin-Based Heteroatom Clusters Studied by the Density Functional Theory

The focus of this study is on compound clusters and, due to the existence of many phases with different structural properties, tin-based materials have been chosen as the reference case. The clusters considered below are of two types: in the first case the clusters have the skeleton of the pure tin clusters and are doped with oxygen and aluminum atoms with composition Sn _x Y _y with Y = Al, O, x = 1, 10 and y = 1, 2. In the second case the clusters have a rutile lattice with a columnar or a spherical shape and a size up to 80 atoms and are doped with a number of aluminum atoms up to 20. The calculations are based on the Density Functional Theory (DFT) and the results describe the cluster structure, its binding energy and the density of states (DOS). The general indication of the calculations is that the additive coordinates outside, rather than inside, the pristine skeleton with the formation of hybrid bonds with properties similar to the ones of the host atoms. Also conspicuous effects of hybridization are observed in the electronic structure and, due to these effects, the binding energy may decrease with respect to the one in the undoped clusters.     

Structures of dense glycine and alanine adlayers on chiral Cu(3,1,17) surfaces

Density Functional Theory calculations have been used to predict the structures of dense glycine and alanine adlayers on Cu(3,1,17)(S). Facets of this chiral Cu surface result from adsorbate-induced surface reconstruction when glycine or alanine are adsorbed and annealed on Cu(100). We have calculated the surface energy changes associated with this surface reconstruction. Our results allow the enantiospecificity of this reconstruction following adsorption of enantiopure or racemic alanine on Cu(100) to be discussed. The overall stability of glycine and alanine adlayers on Cu(3,1,17)(S) arises from an interplay between the formation of chemical bonds with the Cu surface, deformations in the adsorbed molecules during adsorption, and intermolecular hydrogen bonds within the adlayer; none of these factors individually dominates.     

Electrostatic fields E(r) created in the vicinity of cluster-modelled nickel surfaces, using DFT densities

On the basis of self-consistent electronic densities obtained via Density Functional Theory (DFT), we have evaluated the magnitude of the electrostatic fields created in the vicinity of several nickel clusters, from analytically computed electrostatic potentials. These preliminary results are used to examine whether, and how, long-range interactions with metallic surfaces may help an approaching molecule to discriminate one surface site or another.     

(N_2…CO)~+体系相互作用的密度泛函理论研究

在2种密度泛函方法和适宜基组水平上,对(N2…CO)+体系可能存在的相互作用复合物进行了全自由度能量梯度优化,发现势能面上存在2个能量极小点,均为共平面型。 比较了它们之间的相对稳定性,并对其进行了轨道成键分析,同时探讨了最稳定结构A的正则振动模式。 通过消除基函数引起的重叠误差(BSSE)和零点振动能(ZPVE)的校正,精确求算出复合物结构A、B的相互作用能DE分别为125.0和61.0 kJ/mol, 同等电子体(CO…CO)+相比,二者存在较大的差异。     

Theoretical Studies on the Reaction Mechanism of AsCl3 with H2 in the Vapor Phase Epitaxy of GaAs

The reaction mechanism of AsCl3 with H2 has been studied by using the method of BHandHLYP in Density Functional Theory (DFT) at the 6-311G** basis set. The transition state of each reaction is verified via the analysis of vibration mode and Intrinsic Reaction Coordinate (IRC). Meanwhile,single-point energy has been calculated at the QCISD(T)/6-311G** level,and the zero-point energy correction has been made to the total energy and reaction energy barrier. It shows that AsCl3 reacts with H2 to first result in AsHCl2 which may incline to self-decompose and finally afford the product As2,or continue to react with H2 to provide the product AsH3. The computing result demonstrates that the former is the main reaction channel.     

含氮ZSM-5分子筛骨架中氮取代位置的密度泛函计算

运用Gaussian 98程序包, 采用密度泛函理论B3LYP方法, 基于ZSM-5分子筛的8T模型, 分别通过6-31G, 6-31G(d)和6-311G(d,p)基组计算了ZSM-5分子筛中氮原子取代前后各O原子和各N原子的能量, 从而得到各O原子与各N原子在骨架中的稳定性及其对氮化取代反应的影响. 计算结果表明, N原子在骨架中的稳定性对氮取代反应的影响较大. ZSM-5分子筛晶体结构中与B酸位处于同一个四面体的O11位置, 为氮原子的最佳取代位置, 因此氮化后分子筛表面的B酸强度得到较大程度的减弱.     

Reaction of SC+(1D,3D) with H2O, NH3, and CH4: a density functional study.

Density Functional Theory has been used to explore quantitative details of the potential energy hypersurface for the insertion reaction of scandium ion into the O-H, N-H, and C-H bond of water, ammonia, and methane molecules leading to H2 elimination. Both singlet and triplet state channels have been considered. On the basis of the obtained results, it is possible to conclude that for the molecules considered the reaction is a spin-forbidden process. Indeed, it starts in the triplet ground state and ends in the singlet state, the change of the spin state probably occurring immediately after the formation of the electrostatic complex intermediate.     

Density functional calculation of the electronic absorption spectrum of Cu+ and Ag+ aqua ions

The UV absorption of aqueous Cu+ and Ag+ has been studied using Time Dependent Density Functional Theory (TDDFT) response techniques. The TDDFT electronic spectrum was computed from finite temperature dynamical trajectories in solution generated using the Density Functional Theory (DFT) based Ab Initio Molecular Dynamics (AIMD) method. The absorption of the two ions is shown to arise from similar excitation mechanisms, namely transitions from d orbitals localized on the metal center to a rather delocalized state originating from hybridization of the metal s orbital to the conduction band edge of the solvent. The ions differ in the way the spectral profile builds up as a consequence of solvent thermal motion. The Cu+ absorption is widely modulated, both in transition energies and intensities by fluctuations in the coordination environment which is characterized by the formation of strong coordination bonds to two water molecules in an approximately linear geometry. Though, on average, absorption intensities are typical of symmetry forbidden transitions of metal ions in the solid state, occasionally very short (<100 fs) bursts in intensity are observed, associated with anomalous Cu-H interactions. Absorption by the Ag+ complex is in comparison relatively stable in time, and can be interpreted in terms of the energy splitting of the metal 4d manifold in an average crystal field corresponding to a fourfold coordination in a distorted tetrahedral arrangement. Whereas the spectral profile of the Ag+ aqua ion is in good agreement with experiment, the overall position of the band is underestimated by 2 eV in the BLYP approximation to DFT. The discrepancy with experiment is reduced to 1.3 eV when a hybrid functional (PBE0) is used. The remaining inaccuracy of TDDFT in this situation is related to the delocalized character of the target state in d-->s transitions.     

The structures and electronic states of zinc-water clusters Zn(n)(H2O)(m) (n = 1-32 and m = 1-3)

Ab initio and Density Functional Theory (DFT) calculations have been carried out for zinc-water clusters Zn(n)-(H2O)(m) (n = 1-32 and m = 1-3, where n and m are the numbers of zinc atoms and water molecules, respectively) to elucidate the structure and electronic states of the clusters and the interaction of zinc cluster with water molecules. The binding energies of H2O to zinc clusters were small at n = 2-3 (2.3-4.2 kcal mol(-1)), whereas the energy increased significantly in n = 4 (9.0 kcal mol(-1)). Also, the binding nature of H2O was changed at n = 4. The cluster size dependency of the binding energy of H2O accorded well with that of the natural population of electrons in the 4p orbital of the zinc atom. In the larger clusters (n > 20), it was found that the zinc atoms in surface regions of the zinc cluster have a positive charge, whereas those in the interior region have a negative charge with the large electron population in the 4p orbital. The interaction of H2O with the zinc clusters were discussed on the basis of the theoretical results.     

铅硫二元团簇Pb5S+4的理论研究

用密度泛函方法对铅硫二元团簇Ｐb５Ｓ４＋的结构和性能进行了理论研究。结果表明,具 有Ｃ,对称性的笼状结构的异构体最稳定。根据计算所推测的该团簇的性质与实验结果下一致。     

Ultraviolet absorption spectra of substituted phenols: a computational study

Vertical excitation energies for electronic transitions from the ground state to the first two excited states of phenol, mono- and disubstituted methoxyphenols and methyl-substituted phenols have been characterized with the Time-Dependent Density Functional Theory (TD-DFT), the Complete Active Space Self-Consistent Field method (CASSCF) and the Coupled Cluster with Single and Double Excitations Equation-of-Motion approach (CCSD-EOM) to simulate and interpret experimental ultraviolet absorption spectra. While CASSCF excitation energies for the first two transitions either are grossly overestimated or exhibit a weak correlation with experimental data, both TD-DFT and CCSD-EOM perform very well, reproducing the spectral shifts of both the primary band and secondary band observed upon substitution. The conformational dependence of the calculated excitation energies is generally smaller than the shifts caused by substitution.     

Mixed-valence states formation in conformationally flexible metal-free 5,10,15,20-tetraferrocenylporphyrin and 5,10-bisferrocenyl-15,20-bisphenylporphyrin

Metal-free 5,10,15,20-tetraferrocenylporphyrin and 5,10-bisferrocenyl-15,20-bisphenylporphyrin have been prepared and characterized by UV-Vis, MCD, (1)H, (13)C, and variable-temperature NMR, APCI- and ESI-MS, and M?ssbauer spectroscopy, while their redox properties were investigated using electrochemical (cyclic voltammetry and differential pulse voltammetry), spectroelectrochemical, and chemical oxidation approaches. The electronic structure calculations at Density Functional Theory level reveal that both compounds adopt saddle conformations and the HOMOs in both complexes are predominantly metal-centered, while the LUMOs predominantly consist of porphyrin pi* orbitals. In spite of the rotational freedom of ferrocenyl substituents at room temperature, both metal-free 5,10,15,20-tetraferrocenylporphyrin and 5,10-bisferrocenyl-15,20-bisphenylporphyrin are able to form mixed-valence states upon the successive ferrocene-based two- and one-electron oxidations, respectively, as confirmed by UV-Vis, MCD, M?ssbauer, electro-, and spectroelectrochemical methods, and thus, the earlier suggested (Boyd et al. Chem. Commun., 1999, 637) requirements for the formation of mixed-valence states in ferrocene-containing porphyrins should be revised.     

Atomistic Modeling of Silica Based Sol-Gel Processes

Density Functional Theory is used to study water, methanol, ethanol, TMOS, and TEOS molecules and the most important silica clusters participating in sol-gel processes. Calculated bond lengths, bond angles and electric dipole moments compare well with experimental data. The energy of these molecules is reported and used to discuss the energetics of the hydrolysis and condensation reactions. Molecular Dynamics is employed to simulate liquid water, methanol, ethanol, TMOS, TEOS and experimental sol-gel solutions. Calculated densities and enthalpies of vaporisation compare well with experimental data. Preliminary results are presented for MD simulations of sol-gel solutions.     

Thermochromic luminescence of copper iodide clusters: the case of phosphine ligands

Three copper(I) iodide clusters coordinated by different phosphine ligands formulated [Cu(4)I(4)(PPh(3))(4)] (1), [Cu(4)I(4)(Pcpent(3))(4)] (2), and [Cu(4)I(4)(PPh(2)Pr)(4)] (3) (PPh(3) = triphenylphosphine, Pcpent(3) = tricyclopentylphosphine, and PPh(2)Pr = diphenylpropylphosphine) have been synthesized and characterized by (1)H and (31)P NMR, elemental analysis and single crystal X-ray diffraction analysis. They crystallize in different space groups, namely, monoclinic P21/c, cubic Pa ?3, and tetragonal I ?42m for 1, 2, and 3, respectively. The photoluminescence properties of clusters 1 and 3 show reversible luminescence thermochromism with two highly intense emission bands whose intensities are temperature dependent. In accordance to Density Functional Theory (DFT) calculations, these two emission bands have been attributed to two different transitions, a cluster centered (CC) one and a mixed XMCT/XLCT one. Cluster 2 does not exhibit luminescence variation in temperature because of the lack of the latter transition. The absorption spectra of the three clusters have been also rationalized by time dependent DFT (TDDFT) calculations. A simplified model is suggested to represent the luminescence thermochromism attributed to the two different excited states in thermal equilibrium. In contrast with the pyridine derivatives, similar excitation profiles and low activation energy for these phosphine-based clusters reflect high coupling of the two emissive states. The effect of the Cu-Cu interactions on the emission properties of these clusters is also discussed. Especially, cluster 3 with long Cu-Cu contacts exhibits a controlled thermochromic luminescence which is to our knowledge, unknown for this family of copper iodide clusters. These phosphine-based clusters appear particularly interesting for the synthesis of original emissive materials.