Is There a Systematic Strategy

Before we start looking at possible approximations to Exc we need to address whether there will be some kind of guidance along the way. If we consider conventional, wave function based methods for solving the electronic Schrodinger equation, the quality of the 

18 We will not digress on that matter here but rather refer the interested reader to the relevant literature, see Perdew and Burke, 1996, or Adamo, di Matteo, and Barone, 1999. 

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