Ab initioabsorption spectra of CdSe clusters

Ab initio absorption spectra for ${\mathrm{Cd}}_n{\mathrm{Se}}_n$ clusters $(1\mathrm{}<~n<~8)$ are calculated using an adiabatic time-dependent density functional formalism within the local density approximation (LDA). We find that the calculated spectra differ significantly from those computed using a simple LDA approach. In particular, they correct for the well-known underestimate of the absorption gap in time-independent density functional theory. The calculated spectra exhibit a variety of features that can be used for comparison against future experimental investigations. In addition, we find a correlation between the highest occupied molecular orbital-lowest unoccupied molecular orbital gap, the optical gap, and the cluster binding energy.