Density functionals Perdew-Wang-91 exchange-correlation

The computation of the electronic structure for each Rc is by using the KS approach with a code designed to use Dirichlet boundary conditions. In this work, we use the Perdew and Wang exchange-correlation functional [33] within the local density approximation [34], Details about this code can be found in Ref. [9] and some applications are in Refs. [35-37],... 

Nonempirical GGA functionals satisfy the uniform density limit. In addition, they satisfy several known, exact properties of the exchange-correlation hole. Two widely used nonempirical functionals that satisfy these properties are the Perdew-Wang 91 (PW91) functional and the Perdew-Burke-Ernzerhof (PBE) functional. Because GGA functionals include more physical ingredients than the LDA functional, it is often assumed that nonempirical GGA functionals should be more accurate than the LDA. This is quite often true, but there are exceptions. One example is in the calculation of the surface energy of transition metals and oxides. 

The results presented here were obtained in the framework of DFT by using a modified version of deMon code [43], All calculations were performed within the nonlocal density approximation employing the gradient-corrected functional of Perdew [44] for correlation and that of Perdew and Wang [45] for exchange energy (PPW) respectively. For some species test calculations using the local potential [46] were carried out. 

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