title: Excitonic effects and optical properties of passivated CdSe clusters.
abstract: We calculate the optical properties of a series of passivated nonstoichiometric CdSe clusters using two first-principles approaches: time-dependent density functional theory within the local-density approximation, and by solving the Bethe-Salpeter equation for optical excitations with the GW approximation for the self-energy. We analyze the character of optical excitations leading to the first low-energy peak in the absorption cross section of these clusters. Within time-dependent density functional theory, we find that the lowest-energy excitation is mostly a single-level to single-level transition. In contrast, many-body methods predict a strong mixture of several different transitions, which is a signature of excitonic effects. The majority of the clusters have a series of dark transitions before the first bright transition. This may explain the long radiative lifetimes observed experimentally.
authors.affiliation: Department of Physics, University of Minnesota, Minneapolis, Minnesota 55455, USA.
authors.forename: Marie Lopez
authors.initials: ML
authors.lastname: del Puerto
authors.forename: Murilo L
authors.initials: ML
authors.lastname: Tiago
authors.forename: James R
authors.initials: JR
authors.lastname: Chelikowsky