The stability of MgH2 has been studied up to 20~GPa using density-functional total-energy calculations. At ambient pressure α-MgH2 takes a TiO2-rutile-type structure. α-MgH2 is predicted to transform into γ-MgH2 at 0.39~GPa. The calculated structural data for α- and γ-MgH2 are in very good agreement with experimental values. At equilibrium the energy difference between these modifications is very small, and as a result both phases coexist in a certain volume and pressure field. Above 3.84~GPa γ-MgH2 transforms into β-MgH2; consistent with experimental findings. Two further transformations have been identified at still higher pressure: i) β- to δ-MgH2 at 6.73 GPa and (ii) δ- to ϵ-MgH2 at 10.26~GPa.
@article{arxiv.cond-mat/0210463,
title = {Pressure-induced structural transitions in MgH${_2}$},
author = {P. Vajeeston and P. Ravindran and A. Kjekshus and H. Fjellvåg},
journal= {arXiv preprint arXiv:cond-mat/0210463},
year = {2009}
}