Theoretical Study of Small Aluminum Clusters and Li Adsorption on the Surfaces

With density functional theory, the globe geometry optimization for both bare Al_n (n = 3, 6) clusters and their corresponding clusters with Li atom at different adsorption sites have been performed. The calculated relative energies indicate that in both Al₃ and Al₆, hollow sites for Li adsorption are slightly more preferable than on-top sites and bridge sites, which are in good agreement with previous experimental studies. Lithium diffusion on the cluster surfaces have also been investigated. The calculated results show that the adsorption and diffusion of Li atom in Al₃ are slightly different from that in Al₆ clusters. In order to investigate the electron population, natural bond orbital (NBO) charge analysis on Al_n and Al_nLi (n = 3, 6) with hollow Li atom are employed. It is found that electron transfer from Li atom to the aluminum clusters happens. The frequency spectra have also been discussed. In both Al₃Li and Al₆Li with hollow Li atom, peaks with highest intensity are found to be related to the Li atom vibration vertical to the cluster surface, indicating its relatively dynamic instability. Compared with the vibration in Al₃Li, the mode in Al₆Li is blue shifted.