First-principles studies on the structural stability of ?-AlH3 under pressure

Pressure-induced structure transitions and electronic structures in ?-AlH3 are investigated using the first-principles plane wave pseudopotential method within the generalized gradient approximation. Our results show that the application of pressure makes the volume contractions 7.5% and 7.7% at the structural transition points from the to Pnma and Pnma to phases, respectively. Based on the electronic structure analysis, the Pnma phase reflects the transformation tendency from ionic to covalent Al?H bond while ionic Al?H bonding is strengthened in the phase with increasing pressure. The Pnma phase exhibits an uncommon tendency from semiconductor-to-insulator transition since the band gap is widened with increasing pressure.