title: Excitations in time-dependent density-functional theory.
abstract: An approximate solution to the time-dependent density-functional theory response equations for finite systems is developed, yielding corrections to the single-pole approximation. These explain why allowed Kohn-Sham transition frequencies and oscillator strengths are usually good approximations to the true values, and why sometimes they are not. The approximation yields simple expressions for Görling-Levy perturbation theory results, and a method for estimating expectation values of the unknown exchange-correlation kernel.
authors.affiliation: Department of Physics, Rutgers University, Frelinghuysen Road, Piscataway, New Jersey 08854, USA.
authors.forename: H
authors.initials: H
authors.lastname: Appel
authors.forename: E K U
authors.initials: EK
authors.lastname: Gross
authors.forename: K
authors.initials: K
authors.lastname: Burke