First-principles WDA calculations for ferroelectric materials

First-principles calculations within the weighted density approximation (WDA) were performed for some common ferroelectric materials. We used a plane-wave basis, the Perdew-Wang pair-distribution function, and shell partitioning. Compared with the local density approximation (LDA), the WDA significantly improves the equilibrium volume of these materials, but it overestimates the ferroelectric instability in BaTiO3 and PbTiO3. We fixed this failure by imposing a better sum rule based on shell partitioning. Because an orbital-dependent xc potential is introduced, shell partitioning complicates calculation of atomic forces. We also investigated a hybrid WDA method, in which WDA is mixed with LDA.