Density-functional study of Si n C n (n = 10–15) clusters (original) (raw)
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A comparative ab initio study of the Si2C4, Si3C3, and Si4C2 clusters
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Various structural possibilities for the Si 2 C 4 and Si 4 C 2 clusters are investigated by employing a basis set of triple-zeta plus polarization quality; electron correlation is generally accounted for by second-order M0ller-Plesset and, in certain instances, by higher-order perturbation (CASPT2) approaches. The building-up principle recently suggested from an analysis of Si 3 C 3 clusters is found to be fully operative for Si 2 C 4 and Si 4 C 2 clusters. A comparison of the structure and stability of various geometrical arrangements in the series C 6 , Si 2 C 4 , Si 3 C 3 , Si 4 C 2 , and S~ shows that linear and planar structures become rapidly less stable if carbons are replaced by silicons and that the three-dimensional bipyramidal forms become less favorable as soon as silicons are exchanged by carbons in the parent S~ structure. The effects can be rationalized in qualitative terms based on differences in silicon and carbon bonding. 6790
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Since carbon molecules with geodesic structures have been detected, the question for potential silicon-based analogues of these species has been raised. The existence of these hypothetical 'silicon balls', however, has not been ascertained so far in spite of several theoretical as well as experimental attempts to do so. Several theoretical approaches have been put forward in the past to explain the experimentally observed features of Si N clusters and thus to account for the obvious dissimilarity between finite systems based on the isovalent elements silicon and carbon, but no comprehensive growth sequence model has been generally accepted for Si N so far. The present work is aimed at an exploration of closed-shell Si N systems, derived from highly symmetric cage-like geometries, in the size range N Յ 26 by means of Hartree-Fock and post-Hartree-Fock procedures. Particular emphasis is placed on the question of the stabilities of these isomers as compared to the corresponding ground states, wherever available. Cohesive energy calculations suggest a tendency towards an increase of cluster stability with the number of constituents for cage-like Si N isomers up to N = 10, while a trend towards destabilization with growing size is found for larger clusters.
Electronic Properties of Silicon - M Binary Clusters (M = C & Na)
MRS Proceedings, 1994
ABSTRACTElectronic properties of silicon-carbon and silicon-sodium binary clusters, produced by laser vaporization, were investigated by photoelectron spectroscopic or photoionization spectroscopic method. The photoelectron spectra of the C1Sim-1- clusters are similar to those of pure Sim- clusters in the peak positions and their envelopes, which is attributed to the similar electronic structure of Si and C atoms, leading to a similar geometry. In contrast, the similarity in the photoelectron spectra is not observed between Cn- and Cn-1Si1 clusters, which is attributed to a change in their geometry; from chain to ring.The ionization energies (Ei) of the SinNam clusters (l≤n≤15) were determined from the threshold energy of their ionization efficiency curves. The clear parallelism between the ionization energy of SinNa and the electron affinity (EA) of Sin is found; there are three local minima at n=4, 7 and 10. This implies the facts that (1) the structure of the SinNa clusters keeps...
2004
The relationship between the polarizability, stability, and the geometry of small-size silicon clusters has been investigated by the density functional theory methods. Results obtained at local density approximation/Vosko-Wilk-Nusair and general gradient approximation/BLYP levels with polarized even-tempered basis set of quadruple quality are presented and compared with those obtained by the B3LYP method, as well as with the ab initio results in recent literature. We have found that the polarizability is directly related to the size of the energy gap between symmetry-compatible bonding and antibonding molecular orbitals, but not necessarily to the size of the HOMO-LUMO ͑highest occupied molecular orbital-lowest unoccupied molecular orbital͒ gap. Furthermore, we have defined two structural parameters, namely, the averaged Si-Si distances and the standard deviation of the Si-Si distances, which were found to correlate remarkably well with the binding energy of the clusters and the HOMO-LUMO gap, respectively. These straightforward correlations would, therefore, provide a means to predict the physical properties, in particular, the polarizability and the stability, simply based on the structural information of the cluster.
The Journal of Chemical Physics, 2004
The relationship between the polarizability, stability, and the geometry of small-size silicon clusters has been investigated by the density functional theory methods. Results obtained at local density approximation/Vosko-Wilk-Nusair and general gradient approximation/BLYP levels with polarized even-tempered basis set of quadruple quality are presented and compared with those obtained by the B3LYP method, as well as with the ab initio results in recent literature. We have found that the polarizability is directly related to the size of the energy gap between symmetry-compatible bonding and antibonding molecular orbitals, but not necessarily to the size of the HOMO-LUMO ͑highest occupied molecular orbital-lowest unoccupied molecular orbital͒ gap. Furthermore, we have defined two structural parameters, namely, the averaged Si-Si distances and the standard deviation of the Si-Si distances, which were found to correlate remarkably well with the binding energy of the clusters and the HOMO-LUMO gap, respectively. These straightforward correlations would, therefore, provide a means to predict the physical properties, in particular, the polarizability and the stability, simply based on the structural information of the cluster.
Eprint Arxiv Physics 0408016, 2004
The theoretical formalism of local density approximation (LDA) to density functional theory (DFT) has been used to study the electronic and geometric structures of Si m C n (1< m, n < 4) clusters. An all electron 6-311++G** basis set has been used and complete geometry optimizations of different possible structures for a specific cluster have been carried out. Comparisons of the structures and the stabilities of the clusters and their dependence on cluster sizes and stoichiometry have been performed in detail. Binding energies, fragmentation energies, vibrational frequencies, HOMO-LUMO gaps, vertical ionization potentials and vertical electron affinities of the optimized clusters have been investigated and reported in detail. Clusters with equal numbers of silicon and carbon atoms are found to be particularly stable. In particular, based on the simultaneous criteria of high binding energy, high band gap, high ionization potential, and low electron affinity, we believe that Si 3 C 3 is a candidate for a highly stable or a so-called "magic cluster". Results have been compared with other experimental and theoretical results available in the literature.
Structure of nanoscale silicon clusters
Physical Review Letters, 1994
Using the Car-Parrinello method, we have obtained unforeseen structures for the low-lying isomers of Si45 and other midsized Si clusters. They are formed by two shells of atoms, the outer one (cage) being fullerenelike and the inner one (core) consisting of a few atoms saturating dangling bonds. These novel structures provide for the first time a consistent interpretation of the available experimental data, including the reactivity trends and the structural transition at a size of-25 atoms.