APPLICATIONS OF THE GENERALIZED GRADIENT APPROXIMATION TO FERROELECTRIC PEROVSKITES

The Perdew-Burke-Ernzerhof generalized gradient approximation to the d ensity functional theory is tested with respect to sensitivity to the choice of the value of the parameter kappa, which is associated with t he degree of localization of the exchange-correlation hole. A study of structural and dynamical properties of four selected ferroelectric pe rovskites is presented. The originally proposed value of kappa= 0.804 works well for some solids, whereas for the ABO(3) perovskites it must be decreased in order to predict equilibrium lattice parameters in go od agreement with experiments. The effects on the structural instabili ties and zone center phonon modes are examined. The need of varying ka ppa from one system to another reflects the fact that the localization of the exchange-correlation hole is system dependent, and the sensiti vity of the structural properties to its actual value illustrates the necessity of finding a universal function for kappa. [S0163-1829(98)08 141-7].