KINETIC-ENERGY IN DENSITY-FUNCTIONAL THEORY

While Kohn-Sham theory uses the quantum-mechanical operator for kineti c energy, Thomas-Fermi theory replaces this with an effective local po tential. If both theories are based on the exact universal density fun ctional defined by Hohenberg-Kohn theory, it is an interesting questio n whether they should give the same results for N-electron ground stat es. This question is examined and answered in the negative. The incons istency is resolved only by extending the definition of functional der ivatives to encompass linear operators. An exact theory must incorpora te one-electron energies and occupation numbers derived from Kohn-Sham theory.