Ac including the band gap, the effective mass and the effect of dopant ionic radius have been investigated using density functional theory (DFT). The full potential linearized augmented plane wave (FL-LAPW) method was used with the local density approximation (LDA+U). The calculated results indicated that substituting indium atoms by these dopants have a significant influence on the structural and electronic properties of alloyed In2O3 crystals. Lattice parameters expand as a function of dopant ionic radii in the order Sc (9.987Å) < In (10.057Å) < Y (10.187Å) < La (10.446 Å) < Ac (10.546 Å) except for Sc dopant Sc (9.987Å) that shrinks. The band gap is increased with Sc and Y dopant while with Ac and La dopants decreases. The calculations have indicated that there are two band gaps for In2O3. One with a strong optical absorption, as direct band gap occurs from 0.81eV energy level below the top of valence band. The second is a much weaker absorption from top of the valence to the bottom of conduction band. The value of the electron effective mass in the bottom of conduction bands is increased for alloys In2O3. The results show that In 5s states do not have significant hybridization with Sc

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