Density-functional theory study of high hydrogen content complex hydrides Mg(BH4)2 at low temperature

•Mg(BH4)2 is important material for hydrogen storage devices.•The low temperature phase of magnesium borohydride is investigated using DFT.•Electronic and optical properties show that Mg(BH4)2 is a s-types materials.•Elastic constants and the related mechanical properties are reported for first time.•Mg(BH4)2 is stable mechanically and is a promising hydride for transparent materials.

We present a systematic study of the low temperature and hexagonal structure of magnesium borohydride, a crystalline material designed for hydrogen storage purpose. We investigated, using ab-initio calculations, the structural, electronic and optical properties. Our calculated results for structural parameters nicely agree to the experimental measurements. The predicted elastic constants and related mechanical properties demonstrate its profound mechanical stability as well. The analysis of electronic structure reveals an insulator nature with a direct band gap about 6.55 eV in the Γ-Γ direction. This distinguish feature of Mg(BH4)2, like many other hydrides, depicts it as suitable substitute for large band gap material. The bonding behavior was also investigated in detail from the charge densities and effective charge populations. The hydrogen (H2) storage capacity is found to be 14.94 wt.% within a reasonable reaction enthalpy of −44.35 kJ mol−1. This might be easily affordable to consider Mg(BH4)2 as potential material for practical H2 storage devices.

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