Onset of Amorphous Structure in CaCO3: Geometric and Electronic Structures of (CaCO3) n (n?=?2–7) Clusters by Ab Initio Calculations

Electronic structures, vibrational analyses, stabilization energies and amorphicity were analyzed for the most stable configurations of the neutral gas phase clusters of calcium carbonate (CaCO₃) _n (n?=?2?C7). Minimum-energy structures were generated through simulated annealing using a mix of molecular dynamics/semiempirical optimization and then full optimization at the ab initio level (RHF/6-31G*). HF-level results are calibrated versus MP2/6-31G* results. Though many clusters are symmetric, the structural arrangements are not crystalline and resemble neither calcite nor aragonite. In general, greater symmetry means a lower stabilization energy. The BSSE- and zero point energy-corrected stabilization energies appear to plateau at about ?113?kcal/mol when n?=?7. Amorphous clusters start appearing when n?=?4 and the lowest-energy minima for n????5 are of C₁ symmetry. No solvent effect is necessary to induce amorphism.     

Ab Initio Study of Neutral and Charged Copper Bromide (CuBr) n (+) Clusters (n?=?1–6)

A theoretical study in the framework of the density functional theory is performed to investigate the stability, the structural and electronic properties of both neutral and cationic copper bromide clusters (CuBr) _n ⁽⁺⁾, n = 1–6. The most stable isomers are found to be cyclic arrangements. Calculated infrared frequencies are compared with the available experimental spectra. The nature of the ionio-covalent bonding is characterized. The fragmentation, the ionization potentials are also investigated.     

Structures and Electronic Properties of Ni–Al Alloy Clusters from First-Principles Calculations

Using the density functional theory calculations with the PBE exchange–correlation energy functional, we have studied the low-energy structures and electronic properties of Ni–Al alloy clusters for adsorbing or doping an aluminum atom to Ni_n (n = 13, 19, 23, 26, 29 and 55) clusters. The most stable structures of Ni_nAl are viewed as adding an Al atom at the hollow triangle and rhombus site of the icosahedron (n = 13, 55) and double-icosahedron (n = 19, 23, 26 and 29) structures, respectively. For Ni_n?1Al, it can be seen that an Al atom gradually moves from surface (n = 13, 19, 23 and 26) to the interior site (n = 29, 55) in the most stable structures. The electronic properties of the Ni–Al alloy clusters including binding energies, magnetic properties, charge transfer and density of states have also been studied.     

Structural, Electronic, and Magnetic Properties of MB n (M?=?Y, Zr, Nb, Mo, Tc, Ru, n?≤?8) Clusters

The geometries, stabilities, electronic, and magnetic properties of MB _n (M?=?Y, Zr, Nb, Mo, Tc, Ru, n????8) clusters have been systematically investigated by density functional theory. It is shown that the lowest energy structures of MB _n (n????3) clusters can be obtained by substituting one B atom in the lowest energy structures of B _n+1 clusters in most cases. After n????8, the 3D configurations prevail and become the lowest-energy structures. The second-order energy difference and the dissociation energy show YB₇, ZrB₇, NbB₆, MoB₆, TcB₆, RuB₆ clusters possess relatively higher stabilities. The doped-M atoms improve the chemical activity of the host clusters in most cases; but different M atom has different effect on B atom??s electronic structure. The binding strengths are strong between M and B _n , which plays an important role in the M?CB growth mechanisms. It is interesting that the relative orientation between the magnetic moments of the M (M?=?Zr, Nb, Mo, Tc, Ru) atoms and those of its neighboring B atoms exhibits ferromagnetic or antiferromagnetic alignment in contrast to the ferromagnetic alignment of YB _n .     

Study of Structures and Electronic Properties of Pdn-1Pb and Pdn(n≤8) Clusters

Geometric and electronic properties of Pdn-1Pb and Pdn(n≤8) clusters have been studied by using density functional theory with effective core potentials, focusing on the differences between mono- and bimetallic clusters. The average bond length of Pdn-1Pb (n≤8) bimetallic clusters is longer than that of pure palladium clusters except for n = 2 and 3. The most stable structure of Pdn-1Pb (n≤7) is the singlet where there is at least a Pd or Pb atom on its excited state. The energy gaps of Pd-Pb binary clusters are narrower than those of Pdn clusters, and then the chemical activity is strengthened when Pdn clusters are doped with Pb.     

One-Dimensional Intercalation Compound 2 HgS⋅SnBr2: Ab Initio Electronic Structure Calculations and Molecular Dynamics Simulations

The one-dimensional intercalation compound 2 HgS⋅SnBr₂ (figure; white: Hg, light gray: S, dark grey: Sn, and black: Br) is an example of the ability of weak host–guest interactions to induce structural modifications in the HgS host. The stability and dynamic behavior of the intercalation compound and its precursors HgS and SnBr₂ have been analyzed by means of DFT/plane wave calculations. The molecular dynamics simulations facilitate the understanding of the structural rearrangements during the intercalation process.     

Geometries and stabilities of Ag n v (v?=?±1, 0; n?=?21–29) clusters

We performed a systematical study on the lowest-energy structures of the medium-sized silver clusters Ag _n (n?=?21?C29) by using a genetic algorithm coupled with a tight-binding method, and the DFT calculations with Perdew?CWang generalized-gradient approximation. The corresponding cluster ions were also searched based on the neutral cluster structures. It is found that the Ag_21?C23 prefer icosahedron or double-icosahedron as core structures. Ag _n (n?=?24?C27) favor a bulk-like fcc stacking motif. Ag₂₈ and Ag₂₉ tend to high symmetrical structures. The relative stabilities, the ionization potentials and electronic affinities of silver clusters analyzed in the paper are consistent with the experimental data. It is interesting to find that the experimental spectra fit reasonable well the optical absorption spectra obtained with the structures calculated by us.     

Ab Initio Studies on the Structure and Binding Interaction of M~ CO_2(M=Sc,Ti…Zn)

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Theoretical Study of the Structural,Electronic, and Magnetic Properties of Zirconium-doped Aluminum Clusters:Al_nZr(n = 1～14)

The geometrical structures, stabilities, electronic and magnetic properties of Al_nZr(n = 1~14) clusters have been systematically investigated using density functional theory. It is found that for the optimized clusters the zirconium atom prefers to remain on the surface, and the growth patterns are organized as follows: Zr substituted Al_(n+1) clusters or Zr capped Aln clusters as well as Al added Al_(n-1)Zr clusters. All doped clusters exhibit relatively larger average binding energies and magnetic behaviors compared with pure Al_(n+1) counterpart. The calculated fragmentation energies and second-order difference of energies exhibit pronounced odd-even alternation behavior as a function of the cluster size when n = 3~13. In all Al_nZr clusters, there exits internal hybridization in both Al and Zr atoms and charge transfer from Al to Zr atom, which reflects the strong interactions between the two kinds of atoms. The magnetic property analysis shows that the 4d electrons of Zr atom are the main origin for cluster magnetism.     

Theoretical study of group 11 metal–silonyl complexes: M–SiO and M–(SiO)2 (M = Cu, Ag, or Au)

 The spectroscopic properties of M–SiO and M–(SiO)₂ (1–1 and 1–2 complexes with M = Cu, Ag, or Au) have been theoretically studied. It has been shown that both M–SiO and M–(SiO)₂ compounds in their ground state are bent with a metal–Si bonded structure. The calculated M(ns) spin density agrees well with the electron spin resonance experimental data. From a topological analysis, it has been shown that a rather large charge transfer occurs from the metal towards the SiO moiety, and that the M–Si bond energy correlates with the electron density located at the M–Si bond path (bond critical point). Received: 6 July 2000 / Accepted: 11 October 2000 / Published online: 19 January 2001     

Study of Structures and Electronic Properties of Pdn–1Pb and Pdn （n≤8） Clusters

Geometric and electronic properties of Pdn–1Pb and Pdn (n≤8) clusters have been studied by using density functional theory with effective core potentials, focusing on the differences between mono- and bimetallic clusters. The average bond length of Pdn–1Pb (n≤8) bimetallic clusters is longer than that of pure palladium clusters except for n = 2 and 3. The most stable structure of Pdn–1Pb (n≤7) is the singlet where there is at least a Pd or Pb atom on its excited state. The energy gaps of Pd–Pb binary clusters are narrower than those of Pdn clusters, and then the chemical activity is strengthened when Pdn clusters are doped with Pb.     

Ab initio Study on the Molecular Geometry,Electronic Structure and Thermodynamic Properties of Benzotrifuroxan(BTF)

１ＩＮＴＲＯＤＵＣＴＩＯＮＢｅｎｚｏｔｒｉｆｕｒｏｘａｎ（ＢＴＦ）ｉｓａｐｏｗｅｒｆｕｌ，ｈｙｄｒｏｇｅｎｆｒｅａｎｄｒｅｌａｔｉｖｅｌｙｓｅｎｓｉｔｉｖｅｅｘｐｌｏｓｉｖｅ．Ｓｉｎｃｅｔｈｉｓｃｏｍｐｏｕｎｄｗａｓｆｉｒｓｔｐｒｅｐａｒｅｄ，ｉ...     

Atomistic Structures,Stabilities, Electronic Properties,and Chemical Bonding of Boron–Aluminum Mixed Clusters B3Al n 0/−/+ (n = 2–6)

Journal of Cluster Science - Neutral, anionic, and cationic B3Al n 0/?/+ (n?=?2–6) clusters were systematically explored using density functional theory and coupled cluster...     

Quantum chemical topology investigation on structure, electronic properties and interaction of CuNg n + (n?=?1–3, Ng?=?He, Ne)

The structures and stabilities of title clusters have been investigated at CCSD(T) computational level. For the title systems, the geometry with high symmetry is preferred and the n?=?2 systems are more stable than its neighbors. For the Cu?CNg interaction, topological analysis of the electron density field, electron localization function, and positive local energy density represent the intermediate interaction type $ \left( {\nabla^{2}{}_{(3,\; - 1)} \rho > 0\; {\text{and}}\;E\left( r \right) < 0} \right) $ . The interaction region is located by generating reduced density gradient isosurface in the real molecular space.     

Structure and stability of AuXe n Z (n = 1–3, Z = −1, 0, +1) clusters

We have explored the structures and stabilities of AuXe _n ^Z (n = 1–3, Z = ?1, 0, +1) cluster series at CCSD(T) theoretical level. The electron affinities and ionization potentials are correlated to the HOMO–LUMO gaps. The role of the interaction was investigated using the natural bond orbital analysis.     

Stable Structure and Characteristic Spectroscopy of(CH3COCH3)n(n=1～7)Clusters

The stable acetone molecule clusters have been studied by using Beeke's threeparameter(B3LYP)density functional theory(DFT)with standard 6-31G(d)basis set.The calculated results show that the optimal structures of acetone clustets are cyclic and the cycles become larger and larger with the increase of cluster size.The strongest vibration peaks for neutral clusters are C=O stretching vibration.The C=O stretching peaks of cyclic acetone clusters split into double ones when n≥3,the frequencies are red-shifted and corresponding intensities increase with the increase of cluster size.     

Theoretical Studies on the Structures and Stabilities of Charged, Titanium-Doped, Small Silicon Clusters, TiSi n ? /TiSi n + (n?=?1–8)

The structures and stabilities of charged, titanium-doped, small silicon clusters TiSi _n ⁺ /TiSi _n ^? (n?=?1–8) have been systematically investigated using the density functional theory method at the B3LYP/6-311+G* level. For comparison, the geometries of neutral TiSi_n clusters were also optimized at the same level, although most of them have been reported previously (Guo et al., J Chem Phys 126: 234704, 2007). Our results indicate that all neutral TiSi_n clusters favor Si-capped TiSi_n?1 structures, with the lowest energy structure of TiSi₂, TiSi₃, TiSi₄, TiSi₅, TiSi₆, TiSi₇ and TiSi₈ being Si-side-on TiSi adduct, Si-face-capped TiSi₂ triangle, Si-face-capped TiSi₃ trigonal pyramid, Si-face-capped TiSi₄ trigonal bipyramid, Si-face-capped TiSi₅ square bipyramid, Si-face-capped TiSi₆ pentagonal bipyramid, and Si-face-capped TiSi₇ capped pentagonal bipyramid, respectively. The ground state structures obtained herein for the neutral TiSi_n clusters agree well with those of Guo et al. except for TiSi₃ and TiSi₈. Adding or removing an electron greatly changes some ground state structures, i.e. for TiSi₃ ^?/TiSi₃ ⁺, TiSi₅ ^?, TiSi₆ ^?/TiSi₆ ⁺ TiSi₇ ^? and TiSi₈ ^?/TiSi₈ ⁺; others are almost unchanged, e.g. TiSi₂ ^?/TiSi₂ ⁺, TiSi₄ ^?/TiSi₄ ⁺, TiSi₅ ⁺ and TiSi₇ ⁺. Based on the optimized geometries, various energetic properties, including binding energies, fragmentation energies, second-order difference energies, HOMO–LUMO energy gaps, ionization potentials and electron affinities, were calculated for all the most stable isomers. The average binding energies reveal that all of TiSi_n/TiSi _n ⁺ /TiSi _n ^? (n?=?1–8) clusters can continue to gain energy as the size increasing. The fragmentation energies and second-order energy differences suggest that neutral TiSi₅, anionic TiSi₅ ^? and cationic TiSi₆ ⁺ are relatively stable.     

Thermal stability of Ag–Au,Cu–Au,and Ag–Cu bimetallic nanoparticles supported on highly oriented pyrolytic graphite

The formation of Ag–Au, Cu–Au, and Ag–Cu bimetallic particles on the surface of highly oriented pyrolytic graphite was studied by X-ray photoelectron spectroscopy. Samples with the core–shell structure of particles were prepared by sequential thermal vacuum deposition. The thermal stability of the samples was studied over a wide range of temperatures (25-400°C) under ultrahigh-vacuum conditions. The heating of the samples to ~250°C leads to the formation of bimetallic alloy particles with a relatively uniform distribution of metals in the bulk. The thermal stability of the samples with respect to sintering depends on the nature of the supported metals. Thus, the Ag–Au particles exhibited the highest thermal resistance (~350°C) under ultrahigh-vacuum conditions, whereas the Ag–Cu particles agglomerated even at ~250°C.