First principles study of structural and electronic properties of AlnN (n=1-19) clusters

The structural and electronic properties of AlnN (n=1-19) clusters have been investigated using generalized gradient approximation to the density functional theory. The lowest-energy structures of AlnN clusters are given based on the extensive search of the local minima of the potential energy surface. The results indicate that the nitrogen atom tends to occupy an inside position for n≦10, but prefers a peripheral position with a bulklike coordination beyond n=10. As cluster size increases, an icosahedral-like motif emerges, and the cluster grows based on the mechanism of capping N and extra Al atoms on the icosahedron of Al13. It is found that Al3N and Al7N exhibit particularly high stability. The AlN bonds may simultaneously possess the ionic and covalent bonding characteristics. The calculated HOMO-LUMO gaps exhibit odd-even oscillations as n increases. The vertical ionization potential of the clusters tends to decrease as the cluster size increases, while the vertical electron affinity tends to increase as cluster size increases.