  We present an ab initio study of the relaxations introduced in TiO2 when a Cd
impurity substitutes a Ti atom and the experimental test of this calculation by
a perturbed-angular-correlation (PAC) measurement of the orientation of the
electric-field gradient (EFG) tensor at the Cd site. The ab-initio calculation
predicts strong anisotropic relaxations of the nearest oxygen neighbors of the
impurity and a change of the orientation of the largest EFG tensor component,
V33, from the [001] to the [110] direction upon substitution of a Ti atom by a
Cd impurity. The last prediction is confirmed by the PAC experiment that shows
that V33 at the Cd site is parallel to either the [110] or the [1\bar{1}0]
crystal axis.
