$\mathrm{Mg}({\mathrm{BH}}_4{)}_2$ 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 ${\mathrm{H}}_2$ release. Using first-principles density-functional theory calculations and a newly developed prototype electrostatic ground state search strategy, we predict a new $T=0\mathrm{K}$ ground state of $\mathrm{Mg}({\mathrm{BH}}_4{)}_2$ with $I\overline{4}m2$ symmetry, which is $5\mathrm{kJ}/\mathrm{mol}$ lower in energy than the recently proposed $P{6}_1$ structure. The calculated thermodynamics of ${\mathrm{H}}_2$ release are within the range required for reversible storage.

• Received 26 October 2007

DOI:https://doi.org/10.1103/PhysRevLett.100.135501