Density-functional study of Si n C n (n=10-15) clusters

Density-functional theory with generalized gradient approximation for the exchange-correlation potential has been used to calculate the structural and electronic properties of Si (n) C (n) (n = 10-15) clusters. We find that the Si (n) C (n) 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.