First-Principles Prediction of a Ground State Crystal Structure of Magnesium Borohydride

Mg(BH₄)₂ contains a large amount of hydrogen by weight and by volume, but its promise as a candidate for hydrogen storage is dependent on the currently unknown thermodynamics of H₂ release. Using first-principles density-functional theory calculations and a newly developed prototype electrostatic ground state search strategy, we predict a new T=0 K ground state of Mg(BH₄)₂ with I4̄m2 symmetry, which is 5 kJ/mol lower in energy than the recently proposed P6₁ structure. The calculated thermodynamics of H₂ release are within the range required for reversible storage.