Growth behavior of La @Si n (n=1-21) metal-encapsulated clusters.

Density functional theory involving generalized gradient approximation correlation functional is used to investigate the cluster series La @Si n (n=1-21). We find that the growth process of La @Si n (n=1-21) could be divided into three stages: First, La atom adheres to other Si atoms in the size range of 1<or=n<or=10; then, La atom is surrounded by Si atoms with basketlike structures in the size range of 11<or=n<or=15; finally, La atom is completely encapsulated into the fullerene cage structures in the size range of 16<or=n<or=21. The growth of fullerene cage starts from La @Si 16 and stops at La @Si 20. By studying La @Si n+ cations and La @Si n(-) anions, we find that the La atom charge curves of neutral clusters, cations, and anions have a cross point at La @Si 12. Adiabatic ionization potential and electron affinity are studied too. Lastly, based on the ground state geometries of La @Si n clusters, we simulate the chemical reaction in which La @Si n H2n + cation has been produced and explain why Hiura et al. [Phys. Rev. Lett. 86, 1733 (2001)] only observed La @Si n H2n+ (n=1-4) cations in their experiment.