| Abstract: | The screened-Coulomb exchange model used first in the Xα method and later on in Kohn–Sham density functional theory is reexamined. Based on the well-elaborated framework of the local spin-density approximation, we show that this model is not well suited when systems with a finite number of electrons are concerned, because it does not respect the pair-density sum rule. A proper modification of the model is proposed by reformulating it in terms of a screened-exchange hole and ensuring the sum rule for this hole. As a result, it is shown how the static screened exchange in finite systems is accompanied by a conjugate antiscreened one. The possible consequences of this effect on the application of the screened-Coulomb exchange model are discussed. © 1994 John Wiley & Sons, Inc. |
