Structure, stability and superhalogen properties of sodium and magnesium borohydrides

First-principles calculations based on the density functional theory (DFT) are performed to study the structure, stability and electron affinity of sodium and magnesium borohydrides. With successive attachments of BH4 complexes to the metal atom a superhalogen behavior is identified for the Na( BH 4 )2 and Mg(BH4)3 clusters, whose electron affinities reach 5.07 eV and 5.13 eV, respectively. As Mg(BH4)3 cluster is used as a building block to decorate the Mg atom the electron affinity is pushed up to a higher level (6.18 eV) which classifies the Mg[Mg(BH4)3]3 moiety as a hyperhalogen.