Study on the structures and properties of (Mg (BH₄)₂)_n clusters by density functional theory

The structures of (Mg (BH₄)₂)_n (n = 1-3) clusters are optimized at 6-31 G* basis set using the hybrid density functional B3LYP method in density functional theory. Geometric structure optimization of the spin multi-degree takes 1, 3, 5 and other conditions to calculate. The most stable isomers, electronic structures, vibrational properties, bonds properties, and ionization potentials are analyzed. The results show that the most stable structure of the cluster is easy to form a chain structure, in which the Mg-B bond length is 0.210 ∼ 0.253 nm, the B-H bond length near the Mg atom in the -BH₄ group is about 0.125 nm, and the B-H bond away from the Mg atom is 0.119 nm. The comparative study of spectrum between clusters and crystal shows that the structure of -BH₄ in clusters is consistent with that in crystal. The natural charges are 1.687 ∼ 1.757 e for Mg atoms, -0.702 ∼ -0.788 e for B atoms, and -0.094 ∼ 0.070 e for H atom, respectively. The interaction between Mg atoms and -BH₄ groups in the clusters shows strong ionic properties and Mg (BH₄)₂ clusters have relatively high kinetic stability. (authors)