Magic behavior and bonding nature in hydrogenated aluminum clusters

Ab initio electronic structure calculations have been performed using plane-wave ultrasoft pseudopotentials as well as Gaussian atomic-orbital methods to understand the interaction of hydrogen with aluminum clusters. Our results show large binding energies of a single hydrogen atom on small A1 clusters and large highest occupied and lowest unoccupied molecular-orbital gaps for AlH, Al₇H, and Al₁₃H making these species behave like magic clusters. In general the binding energy of H is found to decrease with an increase in the cluster size. Calculations on two hydrogen atoms on Al clusters show large binding energies for Al_nH₂ with n = 2, 4, 6, and 8, but a significant decrease for Al₇H₂ as compared to Al₇H. These results confirm the magic behavior of Al₇H and suggest that hydrogen should be dissociated on Al₆, in excellent agreement with the available experimental data.