k-Al2O3 is a metastable phase of alumina. We have investigated the electronic structure and optical properties of -Al2O3 by a first-principles calculation in the framework of density functional theory (DFT) and the full potential linearized augmented plane wave (FP-LAPW) with three different potentials: the generalized gradient approximation (GGA), the local density approximation (LDA), and the Engle-Vosco approximation (EVA). The results were compared with the stable phase -Al2O3. Our calculated value for the direct band gap of -Al2O3 is 7.2 eV, which is very close to its experimental measurement. A direct band gap of 5.95 is obtained for a-Al2O3 which is about 1.25 eV smaller than that of -Al2O3. The calculated optical reflectivity, optical conductivity, and electron energy loss spectrum for - and -Al2O3 are similar on the whole, and for -Al2O3 are in excellent agreement with the experimental measurements.

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