The Quest for Approximate Exchange-Correlation Functionals

The quest for various approximations for the exchange-correlation energy density/(p) has spanned decades in quantum chemistry and was recently reviewed [92]. Here, we will present the red line of its implementation, as it will be further used for the current applications. The benchmark density functional stands as the Slater exchange approximation, derived within the so-called Xa theory [179] ... 

Keeping up with the quest for a most accurate exchange-correlation functional, another appropriate strategy is to use the exact exchange energy calculated with the HE method and the Kohn-Sham orbitals, and rely on approximate functionals only for the part that HE misses, i.e. the electron correlation (2.49). The exchange-correlation functionals based on this strategy are commonly known as hybrid functionals. 

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