  The equilibrium structures and electronic excitation spectra of the Ir(III)
photosensitizer Ir(ppy)$_2$(bpy)]$^+$ bound to medium-sized silver clusters
Ag$_n$ ($n=$19, 20) are investigated using time-dependent density functional
theory. The long-range corrected LC-BLYP approach is used with a
system-specific range separation parameter. The weak physisorption of the
hybrid complexes yield only small changes in the broadened absorption spectra
of the hybrid system as compared with its constituents. However, the density of
states as well as the fine structure of the spectra is strongly modified upon
complexation. It is shown that the standard range separation parameter (0.47
bohr$^{-1}$) cannot predict these properties correctly and the optimized value
of 0.16 bohr$^{-1}$ should be used instead.
