Quantum critical benchmark for density functional theory
  Two electrons at the threshold of ionization represent a severe test case for electronic structure theory. A pseudospectral method yields a very accurate density of the two-electron ion with nuclear charge close to the critical value. Highly accurate energy components and potentials of Kohn-Sham density functional theory are given, as well as a useful parametrization of the critical density. The challenges for density functional approximations and the strength of correlation are also discussed. 
Paul E. Grabowski and Kieron Burke
physics.chem-ph physics.atom-ph quant-ph