Zhang, YK; Yang, WT, *Perspective on "Density-functional theory for fractional particle number: derivative discontinuities of the energy" Perdew JP, Parr RG, Levy M, Balduz JL Jr*,
Theoretical Chemistry Accounts: Theory, Computation, and Modeling (Theoretica Chimica Acta), vol. 103 no. 3-4
(February, 2000),
pp. 346-348 [Gateway.cgi], [doi] .
**Abstract:**

*This paper provides an overview of the title paper by Perdew, Parr, Levy and Balduz [Phys Rev Lett 49:1691 (1982)]. The title paper extended density functional theory to fractional electron number by an ensemble approach and proved that the energy is a series of straight lines interpolating its values at integer numbers of electrons. It also established that the highest-occupied exact Kohn-Sham orbital energy is the negative of the ionization energy, and showed that the exchange-correlation potential jumps by a constant as the number of electrons increases by an integer. These results are fundamental and continue to inspire developments in density functional theory.*