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DFT-D Investigation of the Interaction Between Ir(III) Based Photosensitizers and Small Silver Clusters Ag$_n$ ($n$=2-20, 92)

A dispersion-corrected density functional theory study of the photosensitizer [Ir(ppy)$_2$(bpy)]$^+$ and its derivatives bound to silver clusters Ag$_n$ ($n$=2-20, 92) is performed. The goal is to provide a new system-specific set of $C_{\rm 6}^{}$ interaction parameters for Ag and Ir atoms. To this end a QM:QM scheme is employed using the PBE functional and RPA as well as MP2 calculation as a reference. The obtained $C_{\rm 6}^{}$ coefficients were applied to calculate dissociation curves of selected IrPS-Ag$_n$ complexes and binding energies of derivatives containing oxygen and sulphur as heteroatoms in the ligands. Comparing different $C_{\rm 6}^{}$ parameters it is concluded that RPA-based dispersion correction produces binding energies close to standard D2 and D3 models, whereas MP2-derived parameters overestimate these energies.