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1.
The geometrical parameters of molecular structures of three types of aluminum–iron clusters containing in total four, five, and six Al and Fe atoms in structural units have been calculated by the OPBE/TZVP density functional theory (DFT) method with the Gaussian09 program package. It has been found that the AlFe 3, Al 2Fe 3, and Al 2Fe 4 clusters can have four, eight, and nine structural modifications, which significantly differ in stability and geometric parameters. Bond lengths and bond and torsion (dihedral) angles are reported for each of these modifications. 相似文献
2.
Structures, binding energies, harmonic frequencies, dipole moments, HOMO–LUMO energy gaps and particularly atoms in molecules
(AIM) analyses of some nanoannular carbon clusters (C 4–C 20) are investigated at B3LYP/6-31+G(d) level of theory. No correlation is found by plotting the calculated binding energies
as a functional number of carbon atoms of carbon clusters. The calculated binding energies sharply increase from C 4 to C 10 while slowly from C 10 to C 20. The binding energies of C 4n+2 clusters including C 6, C 10, C 14, and C 18 have a clear increase when compared with others indicating their aromatic characters which is confirmed by results of HOMO–LUMO
energy gaps and geometrical parameters. AIM analyses show that most of our carbon clusters are topologically normal (non-conflict)
with stable structures. Nevertheless, the topological networks of small antiaromatic rings, C 4 and C 8, at their equilibrium geometries may change via molecular vibrations. The existence of straight bond paths in 3D molecular
graphs of carbon clusters with n > 10 implies that ring strains are decreased as the ring sizes grow. Except for C 4 and C 8, the ellipticity values for the remaining carbon clusters are small indicating that the C–C bond is conserved in these clusters.
Dipole moments of even-numbered structures are negligible, whereas odd-numbered ones have μ values of 0.09−0.73 D. 相似文献
3.
The structures and properties of Al
n
, Al
n
+
, Al
n
–
( n=1,5) clusters have been investigated by using the Linear Combination of Gaussian Type Orbitals (LCGTO) method, considering Local (LSD) and Non Local (NLSD) Spin Density Approximations and employing a Model Core Potential (MCP) that allows the explicit treatment of 3 s
2 3 p
1 valence electrons. For each system different geometrical structures and electronic states have been considered. For Al 3, Al
3
+
, Al
3
–
the most stable geometry proved to be the equilateral triangle ( D
3h
). Al 4 and Al
4
+
prefer the rhombus ( D
2h
) structure, while the corresponding anion prefers the square ( D
4h
) one. The trapezoidal form ( C
2v
) is the most stable isomer for Al 5, Al
5
+
and Al
5
–
clusters. The analysis of vibrational frequencies shows that these structures are minima in the potential energy surface. The binding energies ( D
e), the adiabatic ionization potentials (IP) and electron affinities (EA), the chemical potentials or absolute hardnesses () and electronegativities () have been computed. Results are in good agreement with the available experimental data and the previous high level theoretical computations. 相似文献
4.
Geometric parameters of molecular structures of hexatomic heteronuclear (AlFe) clusters with various number of aluminum atoms (Al 2Fe 4 and Al 3Fe 3) were calculated using the density functional hybrid method in the OPBE/TZVP approximation. It was found that the first of these clusters is able to exist in nine and the second in twenty structural modifications substantially differing from each other in their stability and geometric parameters. The values of bond lengths, planar and dihedral (torsion) angles for some of these modifications are given. 相似文献
5.
The structures, electronic and magnetic properties of the FemOn@Cx (m?=?1–3, n?=?1–4, x?=?50, 60) clusters have been investigated by using PBE functional. The C50, C60 can significantly increase the structural stabilities of the FemOn molecules. Fe2O3@C50 and Fe3O4@C50 are more chemically stable than the Fe2O3@C60 and Fe3O4@C60 while FeO@C60 is more chemically stable than the FeO@C50. The spin densities of the FemOn fragments degenerate to zero. Carbon encapsulation leads to the internal charges of the FemOn fragments transfer from 4 s to 4p orbital. 相似文献
6.
Density functional calculations are performed to study the structures and electronic properties of Al
n
Co
m
clusters with n = 1–7 and m = 1–2. Frequency analysis is also performed after structural optimization to make sure that the calculated ground states
are real minima. The corresponding total and binding energies, adiabatic electron affinities and ionization potentials are
presented and discussed to aid the identification of our calculations. The BSSE correction is also considered in our calculation.
Among Al
n
Co
m
, Al
n
Co
m
−, and Al
n
Co
m
= clusters ( n = 1–7 and m = 1–2), Al 4Co −, Al 6Co −, Al 2Co 2, and Al 6Co 2 are predicted to be more stable. Our results are consistent with the available experimental data. 相似文献
7.
The structures, magnetic, and electronic properties of the ground-state (Fe2N)m (m?=?1–4) and (Fe3N)n (n?=?1–3) clusters have been investigated by using first-principles. The structure of the (Fe2N)m and (Fe3N)n clusters is a compromise that the N atoms approach more Fe atoms and the N atoms repel each other. The structural stabilities of the (Fe2N)m and (Fe3N)n clusters increase with the increasing of the N ratio except for the Fe6N3 clusters. The (Fe2N)m (m?=?1–4) and Fe9N3 clusters exhibit more kinetic stabilities than pure iron clusters. The N substitution can decrease the average spin densities of small iron clusters except for the Fe6N2 and Fe8N4 clusters. The Fe–N bonds exhibit certain covalent bond characteristics. 相似文献
8.
In order to understand the catalytic activity of small metal clusters as a function of their size, we have studied the interaction of CH 4 with Al 4 and Al 5 neutral and charged clusters, as well as neutral thermally expanded clusters in the two lowest lying spin states, using density functional theory. These calculations, via extended search, are used to determine the stable positions of H and CH 3 near the cluster, and the transition state to break the H─CH 3 bond. In order to understand the factors underlying the reactivity of the clusters, we have analyzed the electronic structure at the transition state. By an analysis of the change of the electronic density of states close to the transition state, we identify the orbitals involved in the bond breaking process. In conjunction with our previous studies of Al 2 and Al 3 clusters, we find that the small Al clusters, except for Al 5, lower the CH 3─H dissociation barrier with respect to the gas-phase value, although Al lacks occupied d-orbitals. Still, Al 5 does not catalyze methane bond breaking, which is attributed to the required interaction with low-lying Al sp-states. Furthermore, in all cases where stable methyl-aluminum-hydrides are possible, the recombinative desorption of methane is studied by vibrational analysis and application of transition state theory. 相似文献
9.
Genetic algorithm combined with the semi-empirical Hamitonian AM1/PM3 is used to search the low energy isomers of Al n Si m (n = 3, 5, m ≤ 3 and n = 4, m ≤ 4) and the charged clusters with 20 and 28 valence electrons. The candidate structures were optimized by the density functional theory PBE0 and B3LYP models with the triply split basis sets including polarization functions. The electronic structures show that Al–Si binary clusters behave like metal clusters. The molecular orbitals accord with that predicted by the jellium model, and the electron localization function shows the valence electrons are delocalized over the entire clusters. The clusters having 20 and 28 valence electrons exhibit pronounced stabilities and large energy gaps. The 20 valence electrons of Al 4Si 2 and Al 3Si 3 +, Al 5Si ? form closed shells 1 S 21 P 62 S 21 D 10. Al 4Si 4 and Al 5Si 3 ? have oblate structures and the P, D, F levels spilt considerably in these clusters. The electron density distributions suggest that doping silicon in the aluminum clusters enhances the stability considerably. 相似文献
10.
The structural, energetic and magnetic properties of M nC(M = Fe, Co, Ni, Cu, n = 1–6) clusters are systematically investigated by density-functional calculations. We found that the ground-state geometrical structures of M nC clusters are different from those of pure M n+1 clusters. Fe 4C, Ni 2C and Cu 4C possess relatively higher stabilities. Doping of a C atom enhances the binding energy of M n clusters, and the binding energies of Fe n-C, Co n-C and Ni n-C are stronger than that of Cu n-C. 相似文献
11.
Small Si n and Al n clusters ( n = 3–10) were studied with the semiempirical molecular orbital method (MO) method SINDO1. For each n, various structures were optimized to determine the most stable structure. To obtain good qualitative agreement with available ab initio calculations d orbitals had to be omitted from the basis set. Both silicon and aluminum tend to build three-dimensional structures rather than two- or one-dimensional structures, except for n = 3 or 4. The structure growth was studied by approaching various sites of stable structures with one or more atoms. It was found that silicon and aluminum exhibit different structure growth, and consequently, different most-stable structures. Ionization potentials, HOMO -LUMO energy differences, binding energies per atom, and average atomic valencies are presented. 相似文献
12.
The geometrical parameters of the molecular structures of aluminum–chromium and aluminum–molybdenum clusters Al 2Cr 3 and Al 2Mo 3 have been calculated by the OPBE/TZVP density functional theory (DFT) method with the Gaussian09 programL package. It has been found that each of these metal clusters can exist in twenty structural modifications, which significantly differ in stability and geometric parameters. Bond lengths and bond and torsion (dihedral) angles are reported for each of these modifications. 相似文献
13.
With the concept of super-atom, first principles calculations propose a new type of super stable cage clusters Al nH 3n that are much more energetic stable than the well established clusters, Al nH n+2. In the new clusters, the aluminum core-frame acts as a super-atom with n vertexes and 2n Al-Al edges, which allow to adsorb n hydrogen atoms at the top-site and 2n at the bridge-site. Using Al 12H 36 as the basic unit, stable chain structures, (Al 12H 36)m, have been constructed following the same connection mechanism as for (AlH 3) n linear polymeric structures. Apart from high hydrogen percentage per molecule, calculations have shown that these new clusters possess large heat of formation values and their combustion heat is about 4.8 times of the methane, making them a promising high energy density material. 相似文献
14.
应用密度泛函理论在B3LYP/6-311+G(d)水平上研究了硼碳团簇B nC 2 ( n=1~6)的几何结构、生长机制和相对稳定性. 计算结果表明, 对于 n=2~6的簇, 平面多环状构型为最稳定的结构, 其中C原子分布于环的顶点、有尽可能多的三配位硼原子和尽可能多的B—C键. 碳原子作为杂原子倾向掺杂于团簇的顶点位置, 它的掺杂不改变硼团簇的主体结构. 与平面多环状结构相比, 随着簇尺寸的增大, 三维结构和线性链结构更不稳定. 在低能线性结构中, C原子位于链两侧的第二个位置. 计算的碎片分裂能、递增键能以及HOMO-LUMO能隙表明, B 4C 2为幻数簇. 相似文献
15.
The reaction of the K 2[Fe 3Q(CO) 9] clusters (Q = Se or Te) with Rh 2(CO) 4Cl 2 under mild conditions is accompanied by complicated fragmentation of cores of the starting clusters to form large heteronuclear
cluster anions. The [PPh 4][Fe 4Rh 3Se 2(CO) 16] and [PPh 4] 2[Fe 3Rh 4Te 2(CO) 15] compounds were isolated by treatment of the reaction products with tetraphenylphosphonium bromide. The structures of the
products were established by X-ray diffraction. In both compounds, the core of the heteronuclear cluster consists of two octahedra
fused via a common Rh 3 face.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 775–778, May, 2006. 相似文献
16.
The clusters Fe 2Ru(CO) 12–n
(CNBu
t
)
n
( 3, n=1; 4, n=2), FeRu 2(CO) 12–n
(CNBu
t
)
n
( 5, n=1, 6, n=2) and FeRu 2(CO) 11(CNCy) ( 5a) have been prepared by direct substitution from the parent carbonyl precursors Fe 2Ru(CO) 12 ( 1) and FeRu 2(CO) 12 ( 2). All compounds have been characterized spectroscopically and clusters 3, 4, 5, and 6 by single crystal X-ray determinations. In all cases, the isonitrile ligands adopt axial or pseudo-axial positions on a ruthenium atom. The structures of 3– 5 are very similar to their parent clusters, but the extent of metal framework disorder is significantly less. Cluster 6 adopts the same C
2v Fe 3(CO) 12 type structure as 4, and thus differs markedly from the parent compound 2, which has a D
3 structure . 相似文献
17.
Condensed Al 6 Rings in the Subiodides La 3Al 2I 2 and La 2Al 2I The subiodides La 3Al 2I 2 and La 2Al 2I are reported. The compounds were prepared from stoichiometric mixtures of lanthanum, aluminium, and LaI 3 under Ar atmosphere in sealed Ta ampoules at 920–950 °C and 980–1000 °C, respectively. La 3Al 2I 2 crystallizes in space group C2/ m with a = 19.73(2) Å, b = 4.318(1) Å, c = 12.348(9) Å and β = 121.49(3)°, La 2Al 2I in P6 3/ mmc with a = 4.3718(8) Å and c = 17.605(2) Å (isotypic with Gd 2Fe 2I). Both structures are characterized by sheets of trigonal prisms formed by the La atoms centered by aluminium, the latter being arranged in Al 6 rings. These rings are connected to chains in La 3Al 2I 2 (d Al(2)–Al(2) = 2.550(4) Å and 2.615(2) Å, respectively) and layers (d Al–Al = 2.533(1) Å) in La 2Al 2I. Both compounds are metallic conductors. The electronic structure of both compounds is discussed based on band structure calculations. 相似文献
18.
The geometrical and electronic structure of various configurations of molybdenum pentafluoride are studied in the nonrelativistic
approximation of the DV-X α method. It is shown in a cluster approximation that the presence of the MoF 5 monomer with a distorted trigonal bipyramid (C 2v symmetry) and cyclic trimer [MoF 5] 3(D 3h symmetry) configurations is most probable for the liquid and gaseous phases. High probability of the existence of cyclic
tetramers [MoF 5
4 of lower symmetry (D 2h) is confirmed for the crystalline state. The geometrical parameters calculated for the most stable clusters and the data
on their stability agree well with the experimental data. 相似文献
19.
Geometrical and electronic structures of the neutral and singly negatively charged Fe 6O n and Fe 7O m clusters in the range of 1 ≤ n ≤ 20 and 1 ≤ m ≤ 24, respectively, are computed using density functional theory with the generalized gradient approximation. The largest clusters in the two series, Fe 6O 20 and Fe 7O 24, can be described as Fe(FeO 4) 5 and Fe(FeO 4) 6 or alternatively as [FeO 5](FeO 3) 5 and [FeO 6](FeO 3) 6, respectively. The Fe 6O 20 and Fe 7O 24 clusters possess adiabatic electron affinities ( EAad) of 5.64 eV and 5.80 eV and can be attributed to the class of hyperhalogens since FeO 4 is an unique closed‐shell superhalogen with the EAad of 3.9 eV. The spin character of the lowest total energy states in both series changes from ferromagnetic to ferrimagnetic or antiferromagnetic when the first Fe? O? Fe bridge is formed. Oxidation decreases substantially the polarizability per atom of the initial bare clusters; namely, from 5.98 Å 3 of Fe 6 to 2.47 Å 3 of Fe 6O 20 and from 5.67 Å 3 of Fe 7 to 2.38 Å 3 of Fe 7O 24. The results of our computations pertaining to the binding energies of O, Fe, O 2, and FeO in the Fe 7O m series provide an explanation for the experimentally observed abundance of the iron oxide nanoparticles with stoichiometric compositions. © 2016 Wiley Periodicals, Inc. 相似文献
20.
Various nitrogen clusters, N x, are selected for the present theoretical study. The number of nitrogen atoms chosen in this work varies from x = 8 to x = 32. PM3, which is known as one of the best semiempirical methods, is selected for the self-consistent molecular orbital calculations. The geometrical optimization, vibrational frequencies, and thermochemical computations are all involved for various types of molecular nitrogen clusters. The results show that all N x's belong to the category of stable high-energy compounds. Comparison of average bond energy and delocalization energy of all cases reveals that N 20( Ih symmetry) is the most stable molecule among all the nitrogen clusters studied. In addition, our results show five-membered rings are the most favored in the structures of nitrogen clusters (N x). © 1996 John Wiley & Sons, Inc. 相似文献
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