  The quantum states and thermodynamical properties of the Te vacancy in CdTe
are addressed by first principles calculations, including the supercell size
and quasiparticle corrections. It is shown that the 64-atoms supercell
calculation is not suitable to model the band structure of the isolated Te
vacancy. This problem can be solved with a larger 216-atoms supercell, where
the band structure of the defect seems to be a perturbation of that of the
perfect crystal. It is interesting to note that the Te-vacancy formation energy
calculated with both supercell sizes are close in energy, which is attributed
to error cancelation. We also show that the interplay between supercell size
effects and the band gap underestimation of the generalized gradient
approximation strongly influences the predicted symmetry of some charge states.
