We report a first-principles study on the structural properties, the electronic structure and the hyperfine properties of the pure, Cd-, and Ta-doped yttria (Y2O3) using the Gauge-Including Projector Augmented Waves (GIPAW) method. The purpose of this work is to assess the accuracy of the GIPAW method for the prediction of the electric field gradient (EFG) at the impurity sites. We analyzed the local structural variations in Y2O3 due to cationic substitution with acceptor (Cd) or donor (Ta) impurities, and how these structural changes modify the electronic structure through the appearance of impurity levels in the density of states. Furthermore, relations between the local structural changes and the variation of the EFGs have been found. From the comparison with available experimental data, we conclude that impurities try to reconstruct local environments similar to those of their respective oxides, and are completely ionized. In addition, this work shows that the GIPAW method is very suitable to calculate accurately the EFG at Cd and Ta impurity sites, as an alternative to the all-electron methods.