Ab initio calculations are performed to investigate the structural stability, electronic structure and mechanical properties of rubidium metal hydrides RbMH4(M = B, Al, Ga) for five different crystal structures, namely hexagonal(P63mc), tetragonal(P42/nmc), tetragonal(P421c), orthorhombic(Pnma) and monoclinic(P21/c). Among the considered structures, tetragonal(P421c) phase is found to be the most stable one for these metal hydrides at normal pressure. A pressure-induced structural phase transition from tetragonal(P421c) to monoclinic(P21/c) phase is observed in all the three metal hydrides. The electronic structure reveals that these hydrides are wide band gap semiconductors. The calculated elastic constants indicate that these alkali metal tetrahydrides are mechanically stable at normal pressure.
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