title: Double excitations within time-dependent density functional theory linear response.
abstract: Within the adiabatic approximation, time-dependent density functional theory yields only single excitations. Near states of double excitation character, the exact exchange-correlation kernel has a strong dependence on frequency. We derive the exact frequency-dependent kernel when a double excitation mixes with a single excitation, well separated from the other excitations, in the limit that the electron--electron interaction is weak. Building on this, we construct a nonempirical approximation for the general case, and illustrate our results on a simple model.
authors.affiliation: Department of Physics and Astronomy, City University of New York and Hunter College, New York, New York 10021, USA. nmaitra@hunter.cuny.edu
authors.forename: Neepa T
authors.initials: NT
authors.lastname: Maitra
authors.forename: Fan
authors.initials: F
authors.lastname: Zhang
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Cave
authors.forename: Kieron
authors.initials: K
authors.lastname: Burke