Growth, magic behavior, and electronic and vibrational properties of Cr-doped Si clusters

Abstract

Silicon clusters doped with a Cr atom have been studied using ab initio plane-wave ultrasoft pseudopotential and Gaussian methods. The most stable structures and magic clusters have been determined for ${\mathrm{Si}}_{n\mathrm{Cr}}$ $(n=8--17)$ starting from many initial configurations. Our results show that for $n=8--11$ the number of Si atoms is not enough to surround a Cr atom fully and therefore the structures of these clusters are basket type in which the Cr atom has a bare part. A cage structure is formed for $n=12$. $\mathrm{Cr}@{\mathrm{Si}}_{12}$ and $\mathrm{Cr}@{\mathrm{Si}}_{15}$ show magic behavior. Among the charged clusters, anion of $\mathrm{Cr}@{\mathrm{Si}}_{12}$ and cation of $\mathrm{Cr}@{\mathrm{Si}}_{13}$ have high stability. The ionization potentials and electron affinities have been calculated. The dynamical stability of clusters is studied from vibrational calculations. The results of Raman activities and infrared intensities are presented for selected clusters. These can be used to identify the structures from experiments. The bonding nature in $\mathrm{Cr}@{\mathrm{Si}}_{n}$ clusters is found to change depending on the structure even when the cluster size is the same.