Pseudopotential study of binding properties of solids within generalized gradient approximations: The role of core-valence exchange correlation

In ab initio pseudopotential calculations within density-functional theory, the nonlinear exchange-correlation interaction between valence and core electrons is often treated linearly through the pseudopotential. We discuss the accuracy and limitations of this approximation regarding a comparison of the local-density approximation (LDA) and generalized gradient approximations (GGA's), which we find to describe core-valence exchange-correlation markedly different. (1) Evaluating the binding properties of a number of typical solids, we demonstrate that the pseudopotential approach and the linearization of core-valence exchange correlation are both accurate and limited in the same way in the GGA as in the LDA. (2) Examining the practice to carry out GGA calculations using pseudopotentials derived within the LDA, we show that the ensuing results differ significantly from those obtained using pseudopotentials derived within the GGA. As principal source of these differences we identify the distinct behavior of core-valence exchange correlation in the LDA and GGA which, accordingly, contributes substantially to the GGA-induced changes of calculated binding properties.