Geometry and electronic structure of (SiO2)3 clusters (original) (raw)
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New Hollow SiO2 Clusters: Structure, Energy and Electronic Characteristics
Structural, energetic and electronic properties of polyhedral silica clusters are studied using density-functional theory. Topology of polyhedral clusters is considered, and a new type of clusters is proposed. For two topological types of clusters (trigonal and tetragonal), new stable structures have been found. The dependences of bonding energy and HOMO-LUMO gap on the geometry of a cluster are analyzed.
The Journal of Chemical Physics, 2009
In this paper we found the most stable structures of silicon-oxide clusters of Si 6 O m ͑m =1-11͒ by using the genetic algorithm. In this work the genetic algorithm uses a semiempirical energy function, MSINDO, to find the best cluster structures of Si 6 O m ͑m =1-11͒. The best structures found were further optimized using the density functional theory. We report the stable geometries, binding energies, lowest unoccupied molecular orbital-highest occupied molecular orbital gap, dissociation energies for the most favorable fragmentation channels and polarizabilities of Si 6 O m ͑m =1-11͒. For most of the clusters studied here we report structures not previously found using limited search approaches on common structural motifs.
The Journal of chemical physics, 2013
The structures, energies, isomerization, and decomposition pathways of small ionic silicon oxide clusters, SiO(n)(+) (n = 3, 4), on doublet and quartet energy surfaces are investigated by density functional theory. New structural isomers of these ionic clusters have been obtained with this systematic study. The energy ordering of the isomeric cluster ions on doublet spin surface is found to follow the same general trend as that of the neutral ones, while it differs on the quartet surface. Our computational results reveal the energetically most preferred decomposition pathways of the ionic clusters on both spin surfaces. To comprehend the reaction mechanism, bonding evolution theory has also been employed using atoms in molecules formalism. The possible reasons behind the structural deformation of some isomers on quartet surface have also been addressed. Our results are expected to provide important insight into the decomposition mechanism and relative stability of the SiO(n)(+) clus...
Journal of Computational Chemistry, 2005
The magic number silica clusters [(SiO 2 ) n O 2 H 3 ] Ϫ with n ϭ 4 and 8 have been observed in the XeCl excimer laser (308 nm) ablation of various porous siliceous materials. The structural origin of the magic number clusters has been studied by the density functional theoretical calculation at the B3LYP/6-31G** level, with a genetic algorithm as a supplementary tool for global structure searching. The DFT results of the first magic number cluster are parallel to the corresponding Hartree-Fock results previously reported with only small differences in the structural parameters. Theoretical calculation predicts that the first magic number cluster (SiO 2 ) 4 O 2 H 4 and its anion [(SiO 2 ) 4 O 2 H 3 ] Ϫ will most probably take pseudotetrahedral cage-like structures. To study the structural properties of the second magic number cluster, geometries of the bare cluster (SiO 2 ) 8 , the neutral complex cluster (SiO 2 ) 8 O 2 H 4 , and the anionic cluster [(SiO 2 ) 8 O 2 H 3 ] Ϫ are fully optimized at the B3LYP/6-31G** level, and the corresponding vibrational frequencies are calculated. The DFT calculations predict that the ground state of the bare silica octamer (SiO 2 ) 8 has a linear chain structure, whereas the second magic number complex cluster (SiO 2 ) 8 O 2 H 4 and its anion [(SiO 2 ) 8 O 2 H 3 ] Ϫ are most probably a mixture of cubic cage-like structural isomers with an O atom inside the cage and several quasi-bicage isomers with high intercage interactions. The stabilization of these structures can also be attributed to the active participation of the group of atoms 2O and 4H (3H for the anion) in chemical bonding during cluster formation. Our theoretical calculation gives preliminary structural interpretation of the presence of the first and second magic number clusters and the absence of higher magic numbers.
Structure and Binding of Neutral and Charged Si n H 2 O ( n = 1, 2, 7) Clusters
The Journal of Physical Chemistry A, 1997
The interaction of a water molecule with Si, Si 2 , and Si 7 clusters is studied using local-spin-density (LSD) functional theory, with and without exchange-correlation gradient corrections. Water binds to a Si atom in a triplet state, with a binding energy of 0.704 eV, while it does not bind stably to Si 2 , forming a metastable singlet state Si-Si-OH 2 cluster, whose dissociation into Si 2 + H 2 O involves a barrier. Water binds weakly to Si 7. Binding in the ionized species is much stronger. In all cases binding is through formation of a Si-O bond, with a partial donation of charge from the oxygen, accompanied by the development of a large dipole moment.
Structures and energetics of Si3N2 clusters
Journal of the Brazilian Chemical Society, 2001
Aglomerados mistos de silício e nitrogênio com fórmula Si 3 N 2 foram investigados teoricamente com os métodos SCF e MP2. Dos onze pontos estacionários encontrados abaixo de 80 kcal/mol, oito correspondem a mínimos locais (ML); desses, cinco são estados singletos. Quanto aos tripletos, três ML e um estado de transição (ET) foram caracterizados. O mínimo global corresponde a uma estrutura angular com ligações alternadas silício-nitrogênio, que contrasta com as estruturas lineares de outros aglomerados menores de Si/N. Uma estrutura bipiramidal mais alta em energia 41.0 kcal/mol pode ser vista como um padrão natural para um crescimento tridimensional. Em geral, estruturas com mais ligações SiN são preferidas energeticamente em relação àquelas em que as ligações SiSi predominam. Tentativas para se localizar ET que se correlacionam com os canais de dissociação mais baixos não tiveram sucesso devido à complexa e computacionalmente difícil busca. Apesar disso, garante-se a estabilidade termodinâmica das estruturas I, III, IV e V, sendo a energia do canal mais baixo um limite inferior. A energia de atomização da estrutura do mínimo global é de 420.6 kcal/mol (MP2). Mixed clusters of silicon and nitrogen with formula Si 3 N 2 have been investigated at both SCF and MP2 levels of theory. Of eleven stationary points found below 80 kcal/mol, eight correspond to local minima (LM); of these, five are singlet states. Of the triplets, three LM and one transition state (TS) were characterized. The global minimum corresponds to an angular structure with alternating siliconnitrogen bonds, in contrast with linear ones for other smaller Si/N clusters. A bipyramidal structure 41.0 kcal/mol high in energy can be seen as a natural pattern for tridimensional growing. In general, structures with more SiN bonds are energetically preferred to those in which the SiSi bonds predominate. Attempts to locate TS correlating with the lowest dissociation channels have been unsuccessful due the complex and computationally demanding search. Despite this fact, the thermodynamic stability for structures I, III, IV, and V is guaranteed, being the energy of the lowest channel a lower bound. The atomization energy for the global minimum structure amounts to 420.6 kcal/mol (MP2).
Density-functional study of Si n C n (n = 10–15) clusters
The European Physical Journal D, 2010
Density-functional theory with generalized gradient approximation for the exchange-correlation potential has been used to calculate the structural and electronic properties of SinCn (n = 10−15) clusters. We find that the SinCn clusters prefer cagelike structures. An extensive isomer search shows that the lowest-energy arrangements are those in which the silicon atoms and the carbon atoms form two distinct subunits. It is found that the carbon atoms favor to form fullerene-like structure due to the sp 2-like bond. The silicon atoms are trying to cope with an unfavorable sp 2 environment, but distorted tetrahedra still show up somewhere of the cagelike structures. On the basis of the lowest-energy geometries obtained, the binding energy, HOMO-LUMO gap, Mulliken charge, ionization potential and electron affinity of the clusters have been computed and analyzed. An electronic charge transfer from the Si-populated to the C-populated regions is observed.
Band-structure calculations of SiO/sub 2/ by means of Hartree-Fock and density-functional techniques
IEEE Transactions on Electron Devices, 2000
Ab initio calculations of the full-band structure of SiO are worked out. Both the conduction and valence bands are investigated by means of two different techniques: Hartree-Fock (HF) and density-functional theory (DFT). A number of energy-level diagrams are calculated in order to compare the corresponding density of states in a range of about 10 eV. Different crystal structures of SiO are studied, that are known to be built-up by the same fundamental unit, namely, the SiO tetrahedron. All the analyzed systems are polymorphs of silica; specifically, the -and -quartz, the -and -cristobalite, and the -tridymite.
RHF and DFT Study of the Molecular and Electronic Properties of (SiO2)n and (GeO2)n Nanoclusters
Modern Applied Science, 2018
The study of nanoclusters has attracted a lot of scientific research over the years. This class of materials are important because they bridge the gap between bulk materials and molecular structures. Silicon and Germanium oxides have many applications in semiconductor technology and nanotechnology. In this research work, molecular and electronic properties of Silicon and Germanium dioxide nanoclusters are studied. The results obtained reveal the comparative advantages and disadvantages of using any of the two oxides for particular applications. Restricted Hartree Fock and Density Functional Theory computations of the molecular and electronic properties of (SiO 2) n and (GeO 2) n nanoclusters (n = 1,..,6) are studied. Silicon dioxide clusters are found to have higher thermal energies and lower average bond lengths and are thus more stable than Germanium dioxide clusters. At n = 1, both nanoclusters are non-polar, but gradually become more polar with increase in n. The average polarizability, molecular hyperpolarizability and total thermal energies of the nanoclusters increases with increase in molecular size. Computed values of the electron affinities for (SiO 2) n clusters agree with experimental results. Some of the most intense Infra Red vibrational motions observed in both molecules are anti-symmetric stretching of Si=O/Ge-O and chain in plane, symmetric stretching of the Si=O/Ge-O bonds and chain in plane and symmetric twisting/breathing of the chain(s) in plane. The two nanoclusters are also Raman active at some frequencies.