Optical Properties of Cage Versus Space-Filling Gold Clusters: A TDLDA Study

Recent DFT computations\footnote{J. Wang {\em et al.}, J. Chem. Phys. A {\bf 109}, 9265 (2005).} have revealed that medium size Au$_n$ clusters form hollow cage and space-filling structures that are energetically competitive. In fact, for $n=32$ and 50 the cage structures are more stable than their space-filling counterparts. Here we report results of large-scale computations on the optical absorption spectra of the most stable cage and space-filling forms of Au$_n$, $n=32,38,44,50$. The computations are performed using the time-dependant linear-response density functional formalism within the local- density approximation (TDLDA). We examine the trends in the low-energy ($<$ 6 eV) parts of the spectra as a function of the cluster size and structure and compare them with the predictions of the classical Mie theory.