When excited states are considered and excitation energies are calculated, a quantitative treatment of electron correlations becomes vital. The point is that the correlation-energy contribution to the ground-state energy may be small compared with the dominating contributions of the self-consistent field; however, when energy differences with respect to the ground state are calculated, the changes in the correlation energy may become equal to or even larger than those resulting from changes in the self-consistent field. For example, in a semiconductor (or insulator) like diamond, the energy gap for exciting an electron from the valence into the conduction band is reduced by a factor of 1/2 due to correlations (Chap. 9).
KeywordsInteraction Representation Perturbation Expansion Memory Matrix Heisenberg Representation Exact Ground State
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- 6.1P.J. Bruna, S.D. Peyerimhoff: In Ab Initio Methods in Quantum Chemistry, Part I, ed. by K.P. Lawley (Wiley, New York 1987)Google Scholar
- 6.6E.K.U. Gross, E. Runge: Vielteilchentheorie (Teubner, Stuttgart 1986)Google Scholar
- 6.8J.R. Schrieffer: Theory of Superconductivity (W.A. Benjamin, Reading, MA 1964)Google Scholar
- 6.9G.D. Mahan: Many Particle Physics (Plenum, New York 1981)Google Scholar
- 6.10A.L. Fetter, J.D. Walecka: Quantum Theory of Many-Particle Systems (McGraw-Hill, New York 1971)Google Scholar
- 6.11R. Zwanzig: In Lectures in Theoretical Physics, Vol. 3 (Interscience, New York 1961)Google Scholar