Ab initio investigation of the stability of Si3C3 clusters and their structural and bonding features

Abstract

Abstract. Various structural possibilities for Si 3 C 3 clusters are investigated by ab initio calculations employing basis sets of double-and triple-zeta quality augmented by d polarization functions. Correlation effects are included by a second-order Moeller Piesset perturbation treatment. For the two lowest-lying structures higher-order correlation corrections and multi-reference effects are also included. Bonding features are investigated by two different types of population analyses to obtain insight into the nature of chemical bonding. A total of 17 stationary points were investigated, 14 of which correspond to local minima and three being transition states. The energetically lowest-lying structures are: A "pyramidlike" structure with various multicenter bonds, followed by a es symmetric isomer closely related to the ground state Si 6 structure. Planar structures, favoured in small carbon clusters, lie higher in energy and are transition states. The lowest-lying triplet system is found to be the linear nonsymmetric Si -C-C-C-Si -Si structure, which is calculated to lie about 38 kcalfmole above the singlet ground state. A building-up principle based on bonding criteria is suggested for the occurence of the various structural possibilities.

Vibrational Spectra and Structures of Neutral SimCn Clusters (m + n = 6): Sequential Doping of Silicon Clusters with Carbon Atoms

“…DFT calculations are performed at the TPSS/def2-TZVP level with the resolution of the identity approximation as implemented in TURBOMOLE 6.1 . This computational approach is justified by the satisfactory agreement with previous MP2 calculations, as illustrated in Table S2 in the Supporting Information (SI). , The search for minima was guided by literature reports and the application of basin hopping procedures . If not stated otherwise, all isomers shown in this work are true minima.…”

“…While pure Si m and C n clusters have extensively been studied by both experiment and theory, , much less information is available for their binary clusters. For example, with the notable exception of a single photoelectron spectroscopic study on anions for larger sizes up to Si 7 C n – , experimental spectroscopic characterization of Si m C n has so far been limited to clusters containing only a few Si atoms ( m ≤ 3), with the main focus on chain-like SiC n . − In contrast, numerous quantum chemical calculations for small Si m C n clusters were reported, − ,− and especially relevant for this work are those for the six-atom Si 6– n C n clusters, − ,,, which will be compared to the current experiments and calculations. The major prediction is that the chain-like (linear and monocyclic) structures of C 6 become rapidly less stable upon sequential doping with Si, whereas the three-dimensional bipyramidal structures of Si 6 become less favorable upon successive C doping. , This trend in structural rearrangements within Si 6– n C n as a function of n was rationalized by the strongly decreasing bond strength along the series C–C > C–Si > Si–Si and the high ability of Si for multicenter bonding.…”

Structure and bonding in mixed silicon–carbon clusters and their anions

“…Ϫoccupancy is favored in bonds between Si atoms. 58 The replacement of C by Si in a cluster gives rise to both considerable strain and polar C-Si bonds. Our calculations show that the electrons bind more strongly to C sites, and that the resulting negative charge ͑as measured, for example, by the Mulliken charges͒ tends to repel added electrons into silicon subunits.…”

“…Mühlhäuser and co-workers 57,58 investigated up to 17 different isomers of this cluster by reoptimizing the most stable HF geometries at the MP2͑TZP͒ and MP2͑TZ2P͒ levels. We have studied eight of their most stable structures as well as other geometries, and also find a distorted C s pentagonal pyramid with a C 3 submolecule with apical angle 44°to be the most stable.…”

The structure of silicon doped intermediate size carbon clusters

“…Nevertheless, the use of the HF method is justified here. Mühlhäuser et al 42 have studied the effects of correlation in the Si 3 C 3 cluster by relaxing it using the HF and calculations based on the Møller-Plesset ͑MP͒ theory, which does include correlation. Change in the resulting geometry was found to be minimal ͑around 1% in distances and 3-5 degrees in angles͒ and correlation was found to affect only the relative energies of the different isomers studied.…”