Stability, electronic structure, and optical properties of protected gold-doped silver AgAu (x = 0-5) nanoclusters.

In this work, we used density functional theory (DFT) and linear response time-dependent DFT (LR-TDDFT) to investigate the stability, electronic structure, and optical properties of Au-doped [AgAu(BDT)(TPP)] nanoclusters (BDT: 1,3-benzenedithiol; TPP triphenylphosphine) with x = 0-5. The aim of this work is to shed light on the most favorable doped structures by comparing our results with previously published experimental data. The calculated relative energies, ranging between 0.8 and 10 meV per atom, indicate that several doped AgAu nanoclusters are likely to co-exist at room temperature. However, only the Au-doped [AgAu(BDT)(TPP)] nanoclusters that have direct bonding between Au dopants and phosphines display an enhancement in the electronic transitions at ∼450 nm. This agrees with the main spectral absorption features that have been experimentally reported for the mixture of Au-doped silver AgAu nanoclusters. In addition, the formation of the Au-TPP bond could prevent cluster degradation starting from the detachment of the phosphine molecules, since the Au-TPP bond is stronger by ∼0.4 eV than the analogous Ag-TPP one. Thus, the results presented here show the important role of Au-TPP bonding in determining the stability and optical properties of thiolate/phosphine-protected AgAu nanoclusters.