Combined experimental and computational study of the photoabsorption of the monodoped and nondoped nanoclusters Au 24 Pt(SR) 18 , Ag 24 Pt(SR) 18 , and Ag 25 (SR) 18 .

Assessing the accuracy of first-principles computational approaches is instrumental to predict electronic excitations in metal nanoclusters with quantitative confidence. Here we describe a validation study on the optical response of a set of monolayer-protected clusters (MPC). The photoabsorption spectra of Ag 25 (DMBT) 18 - , Ag 24 Pt(DMBT) 18 2- and Au 24 Pt(SC 4 H 9 ) 18 , where DMBT is 2,4-dimethylbenzenethiolate and SC 4 H 9 is n -butylthiolate, have been obtained at low temperature and compared with accurate TDDFT calculations. An excellent match between theory and experiment, with typical deviations of less than 0.1 eV, was obtained, thereby validating the accuracy and reliability of the proposed computational framework. Moreover, an analysis of the TDDFT simulations allowed us to ascribe all relevant spectral features to specific transitions between occupied/virtual orbital pairs. The doping effect of Pt on the optical response of these ultrasmall MPC systems was identified and discussed.