Structure and electronic properties of Al13X (X=F, Cl, Br, and I) clusters

Theoretical electronic structure studies on the neutral Al13X (X=F, Cl, Br, and I) clusters have been carried out using a gradient-corrected density functional approach. A low-symmetry (ontop: Cs) isomer is found to be the most stable for the Al13X clusters. The shape of the Al13 moieties in the Cs isomers is significantly distorted from the highly symmetric icosahedral structure and is similar to the Al13 cationic structure. The binding energy between Al13 and the halogen atoms increases as X goes from I (2.96eV) to F (5.79eV). Population analysis shows that the bonding of Al13 to the halogen atoms is predominantly ionic. We found that there is a linear relationship between the binding energy of Al13-X and the electronegativity of X. From the calculated binding energies and highest occupied molecular orbital-lowest unoccupied molecular orbital gaps, we conclude that the Al13X clusters are kinetically and thermodynamically stable. The structure of Al13X- clusters is highly symmetric (ontop: C5v), implying that the cluster's extra electron is localized in the Al13 moiety.