Shape Control of Al Nanoclusters by Ligand Size

It is a challenge to synthesize clusters having a certain shape associated with a desirable property. In this study, we perform density functional calculations on ligand-protected Al7 and Al77 clusters. It is found that small ligands such as NH2 still prefer the compact structure of bare Al clusters. However, large ligands such as N(SiMe3)2 stabilize the experimentally observed shell-like structures due to the steric effect. This is different from the Ga84 cluster case where small ligands can stabilize the experimental shell-like Ga84 cluster. Our study suggests that the shape, and thus the properties, of clusters (for instance, C3v Al7 cluster has a finite dipole moment in contrast to the centrosymmetric D3d cluster) can be controlled by using ligands with different sizes.