${\mathrm{AlH}}_3$ and ${\mathrm{Al}}_2{\mathrm{H}}_6$ are very stable molecules with high ionization potentials and low electron affinities. Yet, we report the findings of higher aluminum hydrides, ${\mathrm{Al}}_n{\mathrm{H}}_{3n}$ $(n=3\mathrm{}–7)$ 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 $n=4\mathrm{}$ in cyclic or polymeric forms.

• Received 6 February 2003

DOI:https://doi.org/10.1103/PhysRevA.67.063205