We report a computational study and analysis of the optical absorption processes of Ag20
and Au20 clusters deposited on the magnesium oxide (100) facet, both regular and including point
defects. Ag20 and Au20 are taken as models of metal nanoparticles and their plasmonic response, MgO
as a model of a simple oxide support. We consider oxide defects both on the oxygen anion framework
(i.e., a neutral oxygen vacancy) and in the magnesium cation framework (i.e., replacing Mg++ with a
transition metal: Cu++ or Co++). We relax the clusters’ geometries via Density-Functional Theory
(DFT) and calculate the photo-absorption spectra via Time-Dependent DFT (TDDFT) simulations
on the relaxed geometries. We find that the substrate/cluster interaction induces a broadening and
a red-shift of the excited states of the clusters, phenomena that are enhanced by the presence of an
oxygen vacancy and its localized excitations. The presence of a transition-metal dopant does not
qualitatively affect the spectral profile. However, when it lies next to an oxygen vacancy for Ag20,
it can strongly enhance the
