Kinetic energy as a density functional

Whether or not kinetic energy can be represented in orbital Kohn-Sham equations by an effective local potential has been discussed in several recent publications, reaching conflicting conclusions. It is shown here that this conflict can be resolved by dropping the widespread but unjustified assumption that the existence of a ground-state density functional for the kinetic energy of an N-electron system implies the existence of a density-functional derivative equivalent to a local potential function. For more than two electrons, a density-functional derivative does exist, but has the mathematical character of a linear operator that acts on orbital wave functions. © 2001 The American Physical Society.