  The Perdew-Burke-Ernzerhof generalized gradient approximation to the density
functional theory is tested with respect to sensitivity to the choice of the
value of the parameter $\kappa$, which is associated to the degree of
localization of the exchange-correlation hole. A study of structural and
dynamical properties of four selected ferroelectric perovskites is presented.
The originally proposed value of $\kappa$=0.804 %(best suited for atoms and
molecules) works well for some solids, whereas for the ABO$_3$ perovskites it
must be decreased in order to predict equilibrium lattice parameters in good
agreement with experiments. The effects on the structural instabilities and
zone center phonon modes are examined. The need of varying $\kappa$ from one
system to another reflects the fact that the localization of the
exchange-correlation hole is system dependent, and the sensitivity of the
structural properties to its actual value illustrates the necessity of finding
a universal function for $\kappa$.
