Unconstrained Variational Determination of the Kohn-Sham Potential
  Density Functional Theory's Kohn-Sham (KS) potential emerges as the minimizing effective potential in an unconstrained variational scheme that does not involve fixing the unknown single-electron density. The physical content behind the virtual KS system, that of a non-interacting electronic system representing optimally the interacting one, is brought to light. 
N.I. Gidopoulos