Theoretical investigation on the adsorption of lithium atom on the Si n cluster ( n =2–7)

Ab initio calculations are carried out to study the adsorption of Lithium atom on the Si n cluster with n ranging from 2 to 7. At the MP2/6-31G(d) level, the structures of the neutral Si n clusters and the Si n Li clusters ( n =2–7) are optimized. The single-point energy at QCISD/6-311+G(d,p) level for the optimized isomers are further performed. Harmonic vibrational frequency analysis at the MP2/6-31G(d) level is also undertaken to confirm that the optimize geometries are stable. Based on our results, the most favorable sites for Li adsorption on the Si 2–7 clusters are the bridge sites. In addition, the vertical ionization energies of the Si n Li clusters and the electron affinities of the Si n clusters are also calculated. The clear parallelism between the vertical ionization energies of Si n Li and the electron affinities of Si n is found. This is consistent with the fact that the framework of the Si n in the Si n Li cluster is similar to the structure of the corresponding negative ion Sin−.