Abstract
Koopmans’s theorem is generalized for excited-state ensemble density-functional theory. Formal expressions are derived that relate orbital energy differences to exchange-only excitation energies. These expressions provide stringent requirements for approximating the universal exchange component of the exact exchange-correlation functional for excited-state ensembles, and the expressions lead to a relation, containing a correlation potential, that gives exact excited-state ionization energies.
- Received 20 March 1998
DOI:https://doi.org/10.1103/PhysRevA.59.1687
©1999 American Physical Society
