First–Principle Calculation of the Electronic and Optical Properties of Nanolayered ZnO Polymorphs by PBE and mBJ Density Functionals

 First principle calculations of nanolayered ZnO polymorphs (Wurzite–, Zincblende–, Rocksalt–structures) in the scheme of density functional theory were performedwith the help of full potential linear augmented plane wave (FP-LAPW) method. Theexchange - correlation potential is described by generalized gradient approximation asproposed by Perdew–Burke–Ernzrhof (GGA–PBE) and modified Becke–Johnson (mBJ)approximation. The electronic behavior and the optical properties of the structures areinvestigated and compared to experimental data, where available. The electronic structureof w–ZnO and z–ZnO revealed a 3.01 eV and 2.59 eV direct energy gap in (Γ→Γ)direction by applying mBJ potential. In contrast to w– and z–ZnO the electronic structureof r–ZnO shows an indirect 2.81 eV energy gap in (Γ→L) direction. Reflectivity,transmittance and refractive index spectra for three nano layered of ZnO phases in Uv –visible region have been calculated. The electron effective mass values at the bottom ofconduction band were evaluated for the three geometries.