Stability of Metal-encapsulating Boron Fullerene B40.

The structural stability of MB40 (M = Li, Na, K, Ba, and Ti) is investigated on the basis of density-functional theory calculations at the PBEO level. Particular attention is placed on the relative stability between the endohedral and exohedral configurations of metalloborospherenes. It is found that the Na and Ba atoms can be stably encapsulated inside the B-40 cage, whereas the Li, K, and Ti atoms favor the exohedral configuration where the dopant caps one of heptagons of B-40 cage. In-depth analysis of the endohedral versus exohedral configurations with different dopants suggests that besides the comparable atomic size with the cage size, another key factor that can affect stability of endohedral versus exohedral configuration is the interaction between the dopant and B atoms. The infrared (IR) spectra of the endohedral C-2v Na@B-40 and exohedral C-s Na&B-40 clusters are also computed, from which some useful spectral indictors may be used for identification of the structures in the future experiments.