| Abstract: | The exchange-correlation density functional can be expressed as a many-body perturbation series in terms of the Coulomb interaction using the exact Kohn-Sham orbitals as the basis. A self-consistent equation is derived for the exact exchangecorrelation potential. This perturbation approach forms a basis for going beyond the local density approximation (LDA ). The discontinuity in the exchange-correlation potential for semiconductors calculated by the perturbative approach gives a good account of the discrepancy of the band gap calculated in LDA . The discontinuity also plays an important role in the interface band diagrams. A theory to account for the interaction effects of localized d or f orbitals is reviewed and the physics of the applications to a model test, to some 3d transition metals, and to heavy fermions is discussed. The perturbative approach to improvement beyond LDA tends to be computation-intensive and to be system-specific. © 1995 John Wiley & Sons, Inc. |
