Structural and optical properties of the Ag_n-tyrosine complexes (n=3-12): a density functional theory study

We study the optical properties of Ag-n (n = 3-12) neutral clusters and their coordination with a tyrosine (Tyr) molecule. A global search strategy coupled with density functional theory (DFT) computations explored the potential energy surface. Adsorption energy calculations predicted that Tyr coordination stabilizes the metal clusters, favouring the Ag-n-Tyr complexes with an even number of silver atoms. For the Ag-n low-lying isomers, the general shape and the major transitions of the calculated time dependent-DFT (TD-DFT) absorption spectra align with those of previous reports measured in an argon environment. We use the analysis of non-covalent interactions to identify the specific interactions between each silver cluster and functional groups of Tyr. The TD-DFT absorption spectra for the Ag-n-Tyr complexes showed that Tyr significantly modifies the optical properties of the coordinated silver clusters and affects the smaller systems to a greater extent. The optical absorption results of the bare Ag-n clusters and the Ag-n-Tyr complexes are compared and discussed in detail.