Foundations of Density Functional Theory: Existence Theorems

The starting point of any discussion of DFT is the Hohenberg-Kohn (HK) theorem [6]. It represents the most basic of a number of existence theorems which ensure that stationary many-particle systems can be characterized (fully) by the ground state density and closely related quantities. As the reasoning leading to the HK theorem is quite instructive, it is worthwhile to study this prototype of an existence theorem in some detail (the discussion of the HK theorem follows [7]).