Metastable MgH2 phase predicted by first principles calculations

Abstract

Mg H 2 is a promising compound for hydrogen storage. Its relatively high stability has been the main obstacle for practical applications. Here, the authors report a first principles prediction of a metastable phase of MgH2. The predicted phase is characterized by tetragonal symmetry (I41∕amd, group 141) with the lattice parameters a=0.3813nm and c=0.9416nm and meets all the mechanical stability criteria. Its heat of formation is −58.03kJ∕molH2, which is much less negative than that of the α-MgH2 phase (−76kJ∕molH2). Hence, the tetragonal structure is more desirable than the α-MgH2 for practical hydrogen storage applications.