Structural and Electronic Stabilization Tuning of Al₆N₆ Clusters via Hydrogenation: A Theory Study of Al₆N₆H₈

Investigating aluminum nitride (AlN) clusters is essential for understanding the properties of bulk AlN materials. The incorporation of hydrogen into AlN clusters represents an effective strategy for structural modification and for tuning their physicochemical properties. In this work, we conducted density functional theory (DFT) calculations on the dynamically stable global-minimum (GM) structure of Al₆N₆H₈. Compared to the precursor Al₆N₆ cluster, the incorporation of eight hydrogen atoms achieves coordination saturation of all aluminum and nitrogen atoms, inducing a structural transformation from a hexagonal prism with D_3d symmetry to a cuboid structure with D_2h symmetry. The HOMO-LUMO gap of the Al₆N₆H₈ cluster is increased by 1.85 eV compared to that of Al₆N₆, indicating a remarkable enhancement in stability. Chemical bonding and natural bond orbital (NBO) charge analyses reveal that the Al-N, Al-H, and N-H bonds are predominantly covalent single bonds, with a degree of ionicity arising from electronegativity differences. The hydrogen atoms bonded to Al and N can be substituted with a series of other atoms or functional groups, thereby further tuning the structures and properties of the clusters. To facilitate future experimental characterization, the infrared spectrum of Al₆N₆H₈ was calculated, which shows an overall blue shift in the Al-N bond's bending and stretching vibrations compared to those in the Al₆N₆ cluster.