Structural, Electronic, and Chemisorption Properties of Small Aluminum Clusters

The results of total-energy calculations for optimized structures of ${\mathrm{Al}}_n \mathrm{}(n=2-6\mathrm{})\mathrm{}$ and ${\mathrm{Al}}_n{\mathrm{H}}_2$ are presented in which properties are found to be at variance with the predictions of the electronic shell model. These differences are understood by the introduction of atomic potentials as a perturbation on the shell model. Ionization energies (5.8-6.6 eV) and electron affinities (0.1-2.1 eV) are mostly larger than for an Al atom. Bond lengths increase from 2.51 to 2.81 Å. ${\mathrm{Al}}_6$ is found to be the smallest cluster that will adsorb ${\mathrm{H}}_2$.