Geometric and energetic properties of Al-doped Sin (n = 2-21) clusters: FP-LMTO-MD calculations

We have investigated the effect of aluminum impurity atoms on the geometric structures and stabilities of neutral and ionic Sin (n = 2-21) clusters in detail by using full-potential linear-muffin-tin-orbital molecular-dynamics (FP-LMTO-MD) method. Our calculations suggest that most of the ground state structures for neutral and ionic SinAl (n = 1-20) clusters can be obtained by substituting one Si atom of their corresponding Si clusters with an Al atom. The neutral Sin-1Al clusters with one Al atom have similar geometrical configurations to those of the pure Sin clusters except for local structural distortion. But one Al impurity atom probably reverses the energy ordering of two isomers with small difference. Although, an Al heteroatom reduces the average binding energies for the mixed clusters, it would improve the bond strength between Si atoms in some mixed clusters. Our calculations also suggest that most of the ionic Sin-1Al clusters adopt the same geometrical configurations as their neutral clusters. But for one selected mixed cluster, the charged structures probably have different energy ordering from the neutral clusters. The anionic Sin-1Al− clusters, which are isoelectronic to their corresponding pure Sin clusters, show similar magic behavior.