The optical properties of NiAs phase ZnO under pressure calculated by GGA plus U method

To comprehend the optical properties of the recent-predicted NiAs phase ZnO under pressure, we used the generalized gradient approximation plus U (GGA+U) method to calculate the properties. The GGA+U method is more suited for the strong correlated NiAs phase. The direct band gap increases with increasing pressure. The calculated band gap shows that NiAs phase is an insulator, while the real part (El)(omega) shows the NiAs phase expresses metallic behavior around 18.6 (225 GPa) and 26.0 eV (215 GPa). The relation between the imaginary part (E2)(omega) and PDOS was also discussed. The calculated optical constants show the NiAs phase is transparent and can be used in the vacuum ultraviolet region. We also compared the optical constants of NiAs with wurtzite and CsCl phases ZnO at according transition pressure. And the new-appeared peaks of optical constants can be used to identify the phase transition. The blue-shift optical constants of NiAs phase ZnO can be used to measure pressure after carefully calibrated. Our research provides a reference for identifying and using the NiAs phase ZnO under pressure. (C) 2013 Elsevier B.V. All rights reserved