Cyclic and linear polymeric structures of AlnH3n (n=3-7) molecules

AlH3 and Al2H6 are very stable molecules with high ionization potentials and low electron affinities. Yet, we report the findings of higher aluminum hydrides, AlnH3n (n=3-7) with cyclic or linear polymeric structures that are even more stable. These represent the possibilities of associating higher contents of hydrogen with aluminum clusters. We use first-principles calculations with a plane-wave basis as well as a linear combination of atomic-orbitals method. The binding energies and the highest occupied-lowest unoccupied molecular-orbital gaps of these molecules are significantly higher as compared to the values for the three-dimensional structures of hydrogenated aluminum clusters. The energetic and fragmentation behavior shows that these molecules should be stable up to a size of at least n=4 in cyclic or polymeric forms