Pii: S0166-1280(00)00423-1

We contend that the dependence of traditional density functional theory (DFT) on the one-electron density alone is both its strength and its weakness. We argue that progress beyond Kohn–Sham DFT involves the introduction of two-electron information and present intracules as a natural and concise source of this. We define special cases called the Jand K-intracules and discuss these in the context of both model systems and real molecules. q 2000 Elsevier Science B.V. All rights reserved.