Silicon-Carbon Clusters And Golden Cages: DFT Investigation

Clusters, as a new form of substance, show many novel and unique properties both in physics and chemistry. The detailed knowledge of the atomic structure of clusters, and the dependence of structure on size is an intriguing issue. Due to their unique geometrical arrangements, physical, chemical, electronic and magnetic properties, the studies of clusters can greatly promote the fundamental and applied research of many related subjects, such as physics, chemistry and materials.Geometries, binding energies and electronic structures of SinC13-n (n=1-12) clusters have been investigated using all-electron DFT with BLYP basis set. As the number of silicon atoms increases, the lowest-energy structures transform from planar structures (ring or chain) to three-dimensional structures (3D). It is found that in ground states of SinC13-n (n=1-4) clusters, Si atoms prefer to bond at one or two end(s) of C chain or ring and the lowest-energy structures are all planar structures except the case of Si4C9. Moreover, the lowest-energy configurations of SinC13-n (n=5-12) clusters are all 3D structures. The most stable structures of the SinC13-n (n=5-10) clusters show that carbon atoms preferentially take up positions in the centre of the structures, whereas for the Si11C2 and Si12C clusters, carbon atoms prefer locating at the surface sites. Based on the calculation of the HOMO-LUMO gaps of the ground states, it is found that except for Si6C7 and Si12C, the lowest-energy structures of SinC13-n (n=1-12) have high chemical stability and semi-conductivity. Analysis of the Mülliken population shows that significant charge transfer takes place from the silicon atoms to the carbon atoms.An icosahedron-based template has been proposed and applied to produce a series of icosahedral Aun (n=32, 42, 72, 92, and 122) cages. And then the relativistic density functional theory calculations with GGA/PBE/DSPP basis sets were performed to optimize these structures. Following the new template, two new larger Au92 and Au122 cages are obtained. Compared with the cagelike structure constructed using conventional fullerene-based templates, the hollow cage constructed with the new method is more close to being a stable golden cage. Molecular dynamics calculation and each atom randomly moves 0~0.5 ? have been performed to check their stability, the result shows that they have good stability. Stable Au92 and Au122 cages are (quasi) icosahedrons with Ih symmetry, average Au-Au bond length of Au92 and Au122 cages are 2.797 and 2.792 ?, respectively. Moreover, the HOMO-LUMO gaps of Au92 and Au122 cages are only 0.029 eV and 0.025 eV, respectively, indicating strong metallicity. Analyses of the electronic orbitals show that stable Au92 and Au122 cages are associated with sp-d hybridization, which might be led to by the relativistic effects of heavy element. This work may open a new path for investigating large hollow gold cage. Recently, a new chiral gold cluster of Au72, which satisfies the 2(k+1)2 aromatic rule, is similar to a (quasi) icosahedron, showing the worth and energy of the new icosahedron-based templates in the gold fullerenes studies.