Structural and electronic properties of aluminum-based binary clusters

We investigate the low-energy geometries and the electronic structure of several aluminum based clusters, viz. Al4X4, (X=Li, Na, K, Be, Mg, B, and Si) by first principle Born-Oppenheimer molecular dynamics within the framework of density-functional theory. We present a systematic analysis of the bonding properties and discuss the validity of spherical jellium model. We find that the structure of eigenstates for clusters with metallic elements conform to the spherical jellium model. The 20 valence electron systems Al4Be4 and Al4Mg4 exhibit a large highest-occupied-lowest-unoccupied (HOMO-LUMO) gap due to shell closing effect. In clusters containing alkali-metal atom, Al-4 behaves as a superatom that is ionically bonded to them. The Al-Al bond in both Al4Si4 and Al4B4 clusters is found to be covalent.