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 th eory, the nonlinear exchange-correlation interaction between valence a nd core electrons is often treated linearly through the pseudopotentia l. We discuss the accuracy and limitations of this approximation regar ding a comparison of the local-density approximation (LDA) and general ized gradient approximations (GGA's), which we find to describe core-v alence exchange-correlation markedly different. (1) Evaluating the bin ding properties of a number of typical solids, we demonstrate that the pseudopotential approach and the linearization of core-valence exchan ge correlation are both accurate and Limited in the same way in the GG A as in the LDA. (2) Examining the practice to carry out GGA calculati ons using pseudopotentials derived within the LDA, we show that the en suing results differ significantly from those obtained using pseudopot entials derived within the GGA. As principal source of these differenc es we identify the distinct behavior of core-valence exchange correlat ion in the LDA and GGA which, accordingly, contributes substantially t o the GGA-induced changes of calculated binding properties.