Hydrogen storage capabilities of the most stable isomers of Na_nB_m (m+n=6) clusters

The most stable isomers of Na_nB_m (m+n=6) clusters and their hydrogen storage properties are investigated by means of density functional theory with a 6-311+G(d) basis set. To study the hydrogen storage properties, all of the stable structures of Na_nB_mH_x (m+n=6) clusters have been optimized. It shows that boron atoms of Na_nB_m are separated from the other boron atoms, and form satellite BH_x (x=3, 4) clusters around the centre, which attach to the system by a bridging bond of a hydrogen atom or an Na atom. Compared with the hydrogen storage capabilities, the Na₃B₃ has the highest hydrogen storage capacity among Na_nB_m clusters. The binding energies, interaction energies of hydrogen atom with Na_nB_m clusters and second difference in energy of Na₃B₃H_x clusters have been calculated. The results show that the stability of the Na_nB_mH_x clusters present an odd-even oscillatory effect, as the number of H atoms increases.