A computational study on the endohedral alkali metal and ion B₄₀ nanocluster

Recent exploration of the boron fullerenes has raised exciting new prospects for boron applications. Here, the endohedral X/X⁺@B₄₀ complexes (X = Li, Na, and K) were explored by means of density functional theory calculations. By increasing the atomic number, the interaction of alkali metals with the B₄₀ nanocage is unusually weakened. It was concluded that by increasing the alkali metals' size, their electrons repel those of the cage, and the interaction weakens. The interaction of X with B₄₀ is more favorable than that of X⁺. For example, the calculated ΔG of interaction at 298 K and 1 atm is about -108.3 and + 18.4 kJ mol^-1 for X and X⁺, respectively. Compared to the X⁺ cations, the X atoms considerably enhance the boron cluster electrical conductivity, by reducing the gap. We found that the B₄₀ nanocluster is not large enough to freely embed large atoms, such as Na and K. Also, the electron emission from the surface of B₄₀ cluster is increased and reduced by X and X⁺ encapsulations, respectively.