Density-functional band-structure calculations of magnesium alanate Mg(AlH4)2

Magnesium alanate (Mg(AlH4)2) has been proposed as a candidate material for high-density reversible solid-state hydrogen storage, but so far has not been shown to exhibit reversible hydrogenation. This study presents the calculated crystal structure and electronic structure of Mg(AlH4)2 from density-functional band-structure calculations within the generalized gradient approximation. The calculated structure shows a prolonged c axis compared to the experimental structure; otherwise the agreement is excellent. The electronic density of states shows that magnesium alanate is nonmetallic with a band gap of around 4 eV. The electronic structure analysis implies polar covalent bonds both between Mg and H and between Al and H, with the lowest degree of polarity between Mg and H. The calculated enthalpy of formation suggests that magnesium alanate is metastable at room temperature, and thus not suitable for reversible hydrogen storage