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

Pressure-induced structure transitions and electronic structures in α-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 R 3-bar c to Pnma and Pnma to Pm 3-bar n 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 Pm 3-bar n 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. (paper)