Density functional theory conventional correction schemes

Conventional correction schemes in density functional theory... 

Since the underlying philosophy of DFT is different from that of conventional ab initio theory, so are many of the difficulties encountered. First of all, the resulting hfcc parameters have been shown to depend strongly on functional form. An example of this is shown in Table 4. It has been concluded that for atoms beyond hydrogen, a gradient corrected scheme must be applied for accurate isotropic data. The rationale for this is the insufficient localization of the density, obtained... 

The advantage over the HF scheme is that whereas in conventional ah initio theory we must resort to costly perturbation theory or configuration interaction expansions, in DFT electron correlation is already included explicitly in the exchange-correlation functional. The key problem is instead to find an appropriate expression for xc. As stated above, when we have the correct functional we should be able to extract the exact energy, the exact ground state density, and all properties for our system. 

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