TDDFT and CIS Studies of Optical Properties of Dimers of Silver Tetrahedra

The absorption spectra for dimers of Ag4 +2 and Ag8 clusters at various interparticle distances are examined using time-dependent density functional theory (TDDFT) and configuration interaction singles (CIS) calculations. With TDDFT calculations employing the SAOP functional, minor peaks for Ag4 +2 and Ag8 dimers appear as the interparticle distance decreases; these peaks are suggested to be charge transfer artifacts on the basis of CIS and TDDFT (CAM-B3LYP) calculations. The relationship of the absorption peak locations to the distance and orientation between T d Ag20 dimers is also investigated. TDDFT calculations using the SAOP functional are used to determine excitation absorption spectra for eight different orientations of Ag20 dimers. Although the Ag20 T d monomer has a sharp peak, each dimer absorption spectrum is split due to lower symmetry. This splitting increases as the center of mass distance decreases. As the interparticle distance between the monomers decreases, the initially strong peaks decrease in intensity and red or blue shift depending on symmetry, while the minor peaks increase in intensity and red shift.