Structural and vibronic properties of perovskites studied by using the Perdew–Burke–Ernzerhof GGA

Abstract

The Perdew–Burke–Ernzerhof (PBE) [1] proposal of the Generalized Gradient Approximation (GGA) to Density Functional theory (DFT) was tested against its intrinsic uncertainty in choosing the coefficient κ, which is directly associated to the degree of localization of the exchange-correlation hole. A study of structural instabilities and zone center phonon eigenvalues and eigenvectors is presented. The originally proposed value of 0.804 (best suited for atoms and molecules) works well for some solids, whereas for others 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 of varying κ are examined for selected perovskites. The need of varying κ from one one system to another reflects the fact that the localisation of the exchange-correlation hole is system dependent, and the sensitivity of the physical properties to its actual value illustrates the necessity of finding a universal function for κ=g(∇2n/(2kF)2n).