Atomic and electronic structure of neutral and charged SinOm clusters

Abstract

Using molecular orbital approach and the generalized gradient approximation in the density functional theory, we have calculated the equilibrium geometries, binding energies, ionization potentials, and vertical and adiabatic electron affinities of Si n O m clusters (nр6,mр12). The calculations were carried out using both Gaussian and numerical form for the atomic basis functions. Both procedures yield very similar results. The bonding in Si n O m clusters is characterized by a significant charge transfer between the Si and O atoms and is stronger than in conventional semiconductor clusters. The bond distances are much less sensitive to cluster size than seen for metallic clusters. Similarly, calculated energy gaps between the highest occupied and lowest unoccupied molecular orbital ͑HOMO-LUMO͒ of (SiO 2) n clusters increase with size while the reverse is the norm in most clusters. The HOMO-LUMO gap decreases as the oxygen content of a Si n O m cluster is lowered eventually approaching the visible range. The photoluminescence and strong size dependence of optical properties of small silica clusters could thus be attributed to oxygen defects.

High reactivity of silicon suboxide clusters

“…The HOMO and LUMO variations coincide with a previous finding that the HOMO-LUMO gap decreases as the O content of a Si n O m cluster is lowered. 14 The interesting findings obtained above show that ͑1͒ the HOMO mainly locates at the Si atoms for silicon suboxide clusters (mϽ2n), but at the O atoms for oxygen-rich silicon oxide clusters; ͑2͒ the LUMO for most clusters locates at the Si atoms, particularly for the silicon suboxide clusters; and ͑3͒ the energy difference between HOMO Si and LUMO Si decreases significantly once the atom ratio of O is less than 0.62. From the viewpoint of orbital interaction, the results indicate that, when mϽ2n, the Si atom has a higher reactivity than the O atom and the extent of this reactivity depends on the atom ratio of the O atom.…”

“…The structures obtained in this work are consistent with those found in previous studies. 11,12,14,15,19 The cohesion energies per atom of the deduced configurations of Si n O m clusters as functions of the O atom ratio based on total energy calculations with B3LYP are shown in Fig. 2.…”

Theoretical prediction of atomic and electronic structure of neutral Si6Om (m=1–11) clusters

“…Song and Choi 20 compared the stability of elongated and compact SiO 2 clusters with 12-46 molecules using plane-wave density-functional theory ͑DFT͒ and provided a very good discussion about effects of size, morphology, and different types of silica rings and their electronic and optical properties. Nayak et al 21 studied structure and properties of ͑SiO 2 ͒ n ͑n =1-6͒ and Si 3 O n ͑n =1,3,4͒ employing ab initio methodology, while Zhang et al 19 and Chu et al 22 provided a detailed theoretical study of structures of Si n O m ͑n , m =1-8͒ by the DFT-B3LYP ͑Ref. 23͒ method.…”

Novel structures and energy spectra of hydroxylated (SiO2)8-based clusters: Searching for the magic (SiO2)8O2H3− cluster

“…4,5 Such considerations are particularly difficult to assess for clusters for which the PES exhibits many minima of similar energy with varying degrees of thermal accessibility. 6 From our, and other, investigations into pure [7][8][9][10][11][12] and hydroxylated [13][14][15][16][17] silica nanoclusters, it would appear from the evident rich structural diversity of low energy forms that SiO 2 -based nanostructures possess PES of this type. Indeed, although it is appealing to assign observed prominent peaks in cluster beam mass spectra to a collection of magic clusters all possessing one specific particularly stable structure, it is quite possible that such peaks can correspond to a range of structurally distinct but similarly stable clusters of the same composition and/or to clusters favored, not particularly by stability but rather by facile formation routes.…”