Structural stability and optical properties of AlN explored by ab initio calculations

Pressure-induced structural phase transformations, electronic and optical properties of AlN are investigated by first-principles method based on the plane-wave basis set. The wurtzite (B4), zinc-blende (B3), rocksalt (B1), b-β- Sn, NiAs, anti-NiAs, cinnabar, and simple cubic with 16-atom basis (SC16) phases of AlN have been considered. The calculations demonstrate that there exists a phase transition from B4 structure to B1 phase at the transition pressure of 12.7 GPa. Analysis of band structures suggests that the B4-AlN has a direct gap of 4.13 eV, while B1 phase become indirect under high pressure. The mechanism of these changes of band structures is analyzed. The positive pressure derivative of band gap energies for B1 phase might be due to the absence of d occupations in the valence bands. In addition, the imaginary parts of dielectric function for the polarization in the xy plane and average of the imaginary parts of dielectric function over three Cartesian directions were calculated. The origin of the spectral peaks was interpreted based on the electronic structure.