Density functional investigation of structures and energetics of pure and Sn-doped small lithium clusters

Ground state geometry, energetics, and bonding of pure Li-n (n = 2 - 9) and impure LinSn ( n = 1 - 8) small clusters are investigated using the density functional theory. Introducing a single Sn impurity significantly changes the geometry of the host clusters for n > 5. Although the Sn atom is not trapped inside the cluster, it has the greatest coordination number among other atoms in the cluster. The analyses showed that the nearest neighbor bond lengths in Sn are approximately 10% shorter than those in Li. The results elucidate that the binding energy per atom in impure clusters is greater than that in pure clusters. Finally, it is shown that for Li-8 and Li4Sn clusters that each have with eight valence electrons, the greater gap in the highest occupied molecular orbital and the lowest unoccupied molecular orbital results in a more stable cluster.