Binding-energy and Electronic-structure of Icosahedral Al-cu-(li,mg) Clusters

The binding energy and electronic structure of icosahedral (i-) Al-Cu-(Li,Mg) clusters are investigated using the discrete variational method with local-density-functional theory. The calculations are used to understand differences in local structure and electronic properties between the stable i-Al-Cu-Li and metastable i-Al-Cu-Mg alloys. The calculated results explain phenomenologically that the central site of the Al icosahedron is vacant in Al-Cu-Li, while it is partly occupied by Al in Al-Cu-Mg. They also suggest that the existence and the number of vacant centers should be at least partly responsible for the experimental facts that the density of states at the Fermi energy in the stable i alloys is substantially lower than that in the metastable i alloys and that in the latter it closes to the corresponding free-electron value. The effects of (Li,Mg) in these alloys are also discussed.