Time-dependent density-functional study of the photoabsorption spectrum of Au25(SC2H4C6H5)18anion: Validation of the computational protocol

A validation study of the computational protocol for predicting the optical properties of Monolayer-Protected metal Clusters (MPCs) using time-dependent density-functional theory is presented. The Au25(SC2H4Ph)18- MPC is chosen as a reference, due to the availability of both structural and optical experimental data. The effects of the geometry, the basis set, the exchange-correlation functionals, and the use of simplified or experimental ligands on the optical properties of Au25(SC2H4Ph)18- are discussed critically. When such options are carefully selected, an almost quantitative matching between theory and experiment is obtained. Noteworthy, the use of a precise geometric structure proves to be both crucial and critical for an accurate prediction of the optical response of MPC systems, a feature which is not easy to achieve using current density-functional theory approaches.