Phys. Rev. A 69, 052510 (2004) [6 pages]Adiabatic connection for near degenerate excited statesReceived 25 November 2003; published 25 May 2004 In density functional theory, the adiabatic coupling may be treated perturbatively. This Görling-Levy perturbation theory can be applied to both nondegenerate and degenerate states. Formulas are given to second order. Some excitations are shown to be poorly described to first order (i.e., in exact exchange), no matter how weakly correlated the system is. Results are demonstrated on a simple model system, two fermions in a one-dimensional parabolic well with a contact interaction. © 2004 The American Physical Society URL:
http://link.aps.org/doi/10.1103/PhysRevA.69.052510
DOI:
10.1103/PhysRevA.69.052510
PACS:
31.15.Ew, 31.25.Jf, 31.15.Md, 71.15.Qe
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