[en] We report the results of a study that examines the effects of trivalent Yb impurities occupying different sites in cubic Gd₂O₃ on the latter’s structure and vibrational spectrum. The shell model is employed to compute relaxed structures and phonon symmetrized local densities of states. The lattice structure and dynamics of Yb-doped Gd₂O₃ are calculated using a cluster approach. The frequencies of localized vibrations caused by Yb ions are also determined. The results of lattice-dynamical calculations are compared with experimental data in literature. (paper)