Different evolutionary pathways from B4 to B1 phase in AlN and InN: metadynamics investigations

Pressure-induced B4-B1 phase transitions of AlN and InN at ambient temperature are systematically investigated using density functional-based metadynamics simulations. A homogeneous deformation path, which is energetically favorable, is through a hexagonal structure for AlN, and through a tetragonal structure for InN. Furthermore, the dynamical stability, instead of the mechanical stability, is crucial to determining the phase-transition paths: the intermediate hexagonal structure can remain stable, whereas the tetragonal structure is always unstable. The B4 phase always shows the direct band gap before the occurrence of structure transition, while the band gap of stable intermediate hexagonal phase is indirect for AlN. Finally, the band gap of the ultimate cubic phase is direct for AlN and indirect for InN, due to the strong p-d repulsion at the R point.