In a recent paper, Nesbet [Phys. Rev. A 65, 010502(R) (2001)] has proposed dropping “the widespread but unjustified assumption that the existence of a ground-state density functional for the kinetic energy, $T_{\mathrm{s}}\left[\rho \right],$ of an N-electron system implies the existence of a density-functional derivative, $\delta T_{\mathrm{s}}\left[\rho \right]/\delta \rho \left(\mathbf{r}\right),$ equivalent to a local potential function,” because, according to his arguments, this derivative “has the mathematical character of a linear operator that acts on orbital wave functions.” Our Comment demonstrates that the statement called by Nesbet an “unjustified assumption” happens, in fact, to be a rigorously proven theorem. Therefore, his previous conclusions stemming from his different view of this derivative, which undermined the foundations of density-functional theory, can be discounted.

• Received 3 April 2002

DOI:https://doi.org/10.1103/PhysRevA.66.066501