Further reading
Very good introduction to DFT and HF by Peter Gill
Walter Kohn Nobel lecture:
http://www.nobelprize.org/nobel_prizes/chemistry/laureates/1998/kohn-lecture.pdf
Proofs of Hohenberg-Kohn theorems 1 and 2:
http://www.physics.metu.edu.tr/~hande/teaching/741-lectures/lecture-06.pdf