Structures and energetics of BenGen (n = 1–5) and Be2nGen (n = 1–4) clusters

Cluster geometries and energies of Be_nGe_n (n = 1–5) and Be_2nGe_n (n = 1–4) have been examined in theoretical electronic structure calculations. Structure optimisations were carried out using DFT B3LYP/6-31G(2df) and the energies of the optimum geometries were ordered in QCISD(T) calculations. Be and Ge bond to each other and to other atoms of their own kind, creating a great variety of low-energy clusters in a variety of structural types. Comparisons of the germanide clusters with previously explored silicide and carbide structures reveal some structural similarities, but the germanides have much more in common with the beryllium silicides than with the carbides. However, germanide clusters show a greater tendency to form cage-like structures with potential in technological applications.     

Structure and stability of SiBn+ AND CBn+ (n = 1–4)

The structures and binding energies of small boron-rich clusters are studied using correlated wave functions and polarization basis sets. Carbon is the central atom in CB_n⁺, while SiB_n⁺ prefers planar boron networks with silicon as one of the edge atoms. These ground state structures can be explained by differences in the electronegativities of the component elements. The various fragmentation channels of SiB_n⁺ are also examined using binding energy differences.     

Competitive solvation of K+ by C6H6 and H2O in the K+-(C6H6)n-(H2O)m (n = 1–4; m = 1–6) aggregates

The competitive solvation of the potassium ion by benzene and water is investigated at molecular level by means of Molecular Dynamics simulations on the K⁺-(C₆H₆) _n -(H₂O) _m (n = 1–4; m = 1–6) ionic aggregates. The preference of K⁺ to bind C₆H₆ or H₂O is investigated in the range of temperatures in which isomerisation processes are likely by adding water and benzene to the K⁺-(C₆H₆) _n and K⁺-(H₂O) _m aggregates, respectively. Hydrogen bonds and the π-hydrogen bond, in spite of their weakness with respect to the K⁺-π and K⁺-H₂O interactions, play an important role in stabilising different isomers, thus favouring isomerisation processes. Accordingly with experimental information it has been found that K⁺ bind preferably C₆H₆ rather than H₂O and that the fragmentation of C₆H₆ is only observed for aggregates containing four molecules of benzene.     

Theoretical studies on the structures and absorption spectra of–C n R2n+1(R = H,F; n = 1, 2) substituted 5-(2-pyridyl) pyrazolate boron complexes

The molecular structures, electronic structures and absorption characters of–CH₃,–C₂H₅,–CF₃,–C₂F₅ substituted 5-(2-pyridyl) pyrazolate boron complexes were presented by density functional theory (DFT). The ground state structures of the title complexes were optimised at B3LYP/6-31G* level. In addition, a time dependent density functional theory (TD-DFT) method is applied to investigate the properties of absorption spectra and electronic transition mechanism which were based on the ground state geometries. The results show that the chemical bond formed between nitrogen in the pyridyl ring and boron can be attributed to coordination effect. The boron centre has a typical tetrahedral geometry with the adjacent atoms. The calculated absorption wavelengths for–CF₃,–C₂F₅ substituted 5-(2-pyridyl) pyrazolate boron complexes are in good agreement with the experimental data.     

Structure and chemical valence study of Sr_(n+1)Ru_nO_(3n+1)(n= 1, 2, ∞) series

Effect of structure parameter n and its coupling with the connection mode among RuO6 octahedra of Sr n+1RunO3n+1(n = 1, 2, ∞) are investigated. The gradually enhanced rotation and tilting effect with increasing n are observed in Sr n+1RunO3n+1. Besides, the chemical valence of Ru is not changed, while the one of Sr gradually varies with increasing n, which highlights the great contribution of connection mode to the chemical environment. Our results show a strong n dependence on the connection mode between octahedra in Srn+1RunO3n+1(n = 1, 2, ∞).     

Isotope effect of hydrated clusters of hydrogen chloride,HCl(H2O) n and DCl(H2O) n (n = 0–4): application of dynamic extended molecular orbital method

The recently proposed dynamic extended molecular orbital (DEMO) method is applied to the HCl(H₂O) _n and DCl(H₂O) _n (n = 0–4) clusters in order to explore the isotope effect on their structures, wavefunctions, and energies, theoretically. Since the DEMO method determines both electronic and nuclear wavefunctions simultaneously by optimizing all parameters including basis sets and their centres variationally, we can get the different nuclear orbitals for proton and deuteron as well as their electronic wavefunctions. The positions of the centres of nuclear orbitals show that the deuteron has weaker hydrogen bonding than the proton. There are three isomers in the case of n = 3 clusters, and less stable isomers have hydrogen transferred and non-transferred structures. In the conventional MO calculation, both hydrogen transferred and non-transferred isomers are calculated to be energy minima. When we have applied the DEMO method, only the hydrogen transferred structure is obtained for HCl(H₂O)₃, while both structures are optimized for DCl(H₂O)₃. Such strong H/D dependence on the structures of the HCl(H₂O) _n and DCl(H₂O) _n clusters can be expressed directly by using the DEMO method. The present application demonstrates that the DEMO method is a useful tool for analysing the anharmonicity and vibronic effects of a hydrogen bonding system.     

Mössbauer spectroscopic studies of (n-C n H2n +1NH3)2SnX6 (n=0-4; X = Cl or Br) and their related complexes

Complexes of the type (n-C _n H_2n +1NH₃)₂SnX₆ (0n 4 and X=Cl or Br) have been investigated with a variety of physico-chemical techniques. The structural phase transitions were found in some of these complexes. The temperature dependence of the Mössbauer spectral absorption area for (C₂H₅NH₃)₂SnCl₆ and (C₂H₅NH₃)₂SnBr₆ changed sharply at phase transition temperatures. The temperature dependences for (n-C₄H₉NH₃)₂SnCl₆ and (n-C₄H₉NH₃)₂SnBr₆ decreased gradually with an increase in temperature. The correlation between the temperature dependence of the spectral absorption area and the motion of n-C _n H_2n+1NH₃ ⁺ ions is discussed.     

X-Ray spectral and theoretical investigations of the electronic structure of phenylcyclosilanes (SiPh2) n (n = 4–6)

The X-ray emission SiKα_{1, 2} and SiKβ₁ spectra of a series of phenylcyclosilanes (SiPh₂) _n (n = 4–6) have been obtained. Using the results of quantum-chemical calculations in the density functional theory approximation, the fine structure of SiKβ₁ spectra has been interpreted. Distributions of densities of electron states of silicon atoms over the valence band have been constructed and the types of chemical bonds providing the Si-Si and Si-Ph interactions have been established. Based on the theory of natural bond orbitals, the chemical bonding in the studied series of phenylcyclosilanes has been analyzed.     

Electron-impact multiple ionization of xenon (σn+, n=2–9)

Cross sections for production of multiple charged xenon ions (Xeⁿ⁺, n=2–9) by electron collision are presented in the 100–2500 eV impact energy range. We determinate the apparent ionization thresholds and the integrated oscillator strengths for the reactions. The present values are compared with available data from experimental groups using diverse techniques.     

Mössbauer spectroscopic studies of (n-C n H2n +1NH3)2SnCl6 (n=6, 8-18) complexes

Temperature-dependent Mössbauer experiments have been carried out to examine the lattice-dynamic properties of tin atoms in complexes of the type (n-C _n H_2n+1NH₃)₂SnCl₆ (6 n 12). The temperature dependence of the area intensity of Mössbauer lines for the studied complexes are correlated to the motion of long alkyl chains. Solid-solid phase transitions were clearly found in all the complexes above room temperature, accompanied by an increase in the interlayer spacing (6n 18). The transition temperature and transition entropy increase linearly with the number of carbon atoms in alkyl chains.     

In-plane London penetration depths near the critical temperature of Tl2Ba2Ca n−1Cu n O2n+4 and (Bi,Pb)2Sr2Ca n−1 Cu n O2n+4 (n=2,3)

From isothermalM(H) curves nearT _c , measured on polycrystalline Tl₂Ba₂Ca _n–1Cu _n O_2n +4 and (Bi, Pb)₂Sr₂Ca _n–1Cu _n O_2n+4 (n=2,3) samples, we deduce the in-plane penetration depths _ab as functions of temperature. An estimate according to the BCS weak-coupling clean-limit fit, which produces the data nearT _c very well, yields _ab(0)=3100 Å, 2320 Å 2210 Å, and 1960 Å for Bi₂Sr₂CaCu₂O₈, Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O₁₀, Tl₂Ba₂CaCu₂O₈, and Tl₂Ba₂Ca₂Cu₃O₁₀, respectively. A comparison between strong-coupling and weak coupling fitting curves clearly favours the weak-coupling temperature dependence of _ab nearT _c .     

Density functional theory study of Mg_2Ni_n(n= 1–8) clusters

The density functional theory B3PW91 with LANL2DZ basis sets has been used to study the possible geometries of Mg2Nin(n = 1–8) clusters. For the lowest energy structures of the clusters, stabilities, electronic properties, and natural bond orbital(NBO) are calculated and discussed. The results show that the doped Mg atoms reduce the stabilities of pure Ni clusters. The Mg2Ni2, Mg2Ni4, and Mg2Ni6clusters are more stable than neighboring clusters. The system appears magic number characteristics. In addition, the hybridization phenomenon occurs, owing to the interaction of Mg and Ni. The result of charge transfer is that Ni atom is negative and the Mg atom is positive. We also conclude that the 3p and 4d orbitals of the Ni atom have an effect on the stabilities of the clusters.     

Probing structural and electronic properties of divalent metal Mgn+1 and SrMgn (n=2–12) clusters and their anions

Divalent metal clusters have received great attention due to the interesting size-induced nonmetal-to-metal transition and fascinating properties dependent on cluster size,shape,and doping.In this work,the combination of the CALYPSO code and density functional theory(DFT)optimization is employed to explore the structural properties of neutral and anionic Mg_n+1 and SrMgn(n=2-12)clusters.The results exhibit that as the atomic number of Mg increases,Sr atoms are more likely to replace Mg atoms located in the skeleton convex cap.By analyzing the binding energy,second-order energy difference and the charge transfer,it can be found the SrMg9 cluster with tower framework presents outstanding stability in a studied size range.Further,bonding characteristic analysis reveals that the stability of SrMg9 can be improved due to the strong s-p interaction among the atomic orbitals of Sr and Mg atoms.     

Synthesis and characterization of layered perovskite oxides (La, Sr) n + 1(Ti, Cr) n O3n + 1 (n = 1, 2)

We report here the synthesis of layered perovskite oxides of the composition La_0.5Sr_1.5Ti_0.5Cr_0.5O₄ and LaSr₂TiCrO₇ by conventional solid-state reaction method. Results of XRD analysis show that the phases crystallize with tetragonal unit cell in the space group I4/mmm. Both phases behave as insulators and the linearity of log ρ versus T ^?1/4 plot in the temperature range 150–350 K suggests that the electronic conduction occurs by Mott’s variable range hopping mechanism. The antiferromagnetic interactions observed for the samples arise from Cr³⁺–O–Cr³⁺ superexchange interaction.     

Structures and its evolution of Ba n ( n =2 ∼ 14) clusters

We have studied the atomic structure and the electronic properties of Ba_n clusters by the ab initio molecular dynamics method. We find that a structural transition to the bulk-like structure begins at Ba₉ cluster, and the structures of the clusters are transferred to be icosahedral-like around n = 13. The relatively high stability for Ba₄, Ba₁₀ and Ba₁₃ clusters are observed. Received 1st December 2000     

理论研究C8H8O-(H2O)n(n=1～5)团簇

应用密度泛函B3LYP/6-31 G(d,p)方法对C8H8O-(H2O)n(n=1~5)团簇这种弱相互作用体系进行全自由度能量梯度优化,得到该系列团簇的稳定结构.计算结果表明,在该系列二元团簇中,一方面水分子数目的多少对苯基丙酮分子的结构影响很小,另一方面由于苯基丙酮分子的存在,破坏了团簇中水分子的对称性结构,在团簇内部极力形成O-H-O这样弯曲的有方向性的氢键.对苯基丙酮-水这样结构复杂的团簇,指认光谱的难度非常大,本文只讨论了与C=O有关的振动峰和水分子的对称伸缩振动的最强峰.     

A new global potential energy surface of the ground state of SiH2+ (X2A1) system and dynamics calculations of the Si+ + H2 (v0 = 2, j0 = 0) → SiH+ + H reaction

A global potential energy surface (PES) of the ground state of SiH$_{2}^{+}$ system is built by using neural network method based on 18223 ab initio points. The topographic properties of PES are presented and compared with previous theoretical and experimental studies. The results indicate that the spectroscopic parameters obtained from the new PES are in good agreement with the experimental data. In order to further verify the validity of the new PES, a test dynamics calculation of the Si$^{+} +$ H$_{2}$ ($v_0 = 2, j_{0} = 0$) $\to $ H $+$ SiH$^{+}$ reaction has been carried out by using the time-dependent wave packet method. The integral cross sections and rate constants are computed for the title reaction. The reasonable dynamical behavior indicates that the newly constructed PES is suitable for relevant dynamics investigations.     

Geometric structure and electron spectrum of YSi n − clusters (n = 6–17)

Results of the optimization of the geometric structure of YSi _n ^? anion clusters (n = 6–17) have been presented and their electron spectra have been calculated. Calculations have been performed by the density functional theory method. Actual geometric structures of clusters have been established by comparing the calculated and known experimental data.