  The electronic and optical parameters of {\gamma}-Al2O3 and {\theta}-Al2O3
have been studied by using the first principle within the framework of density
function theory (DFT). The computational approach is based on full-potential
linearized augmented plane wave method (FP-LAPW) within the generalized
gradient approximation (GGA), local density approximation (LDA), and modified
Becke-Johnson potential (mBJ). The results show that these compounds have a
direct gap ({\Gamma}-{\Gamma}) of about 5.375 eV and 4.716 eV for
{\gamma}-Al2O3 and {\theta}-Al2O3, respectively. Several optical parameters of
these materials are also investigated. The values of the real part of
dielectric constant are found to be 3.259 and 3.694 for {\gamma}-Al2O3 and
{\theta}-Al2O3, respectively, which are close to the experimental one (3.416).
The refractive index is 1.806 and 1.922 for {\gamma}-Al2O3 and {\theta}-Al2O3
respectively, and shows a good agreement with the experimental result which is
1.86. GGA findings are consistent with the experimental results and are better
than the other approximations. There are no salient differences between GGA and
LDA results. The results advocate using this material as a transparent
conducting layer in solar cell structure, which can be operated in a wide
energy range.
