Charge Transfer Plasmons in Dimeric Electron Clusters

The tunability of the optical response of dimers of metal clusters and nanoparticles makes them ideal for many applications from sensing and imaging to inducing chemical reactions. We have studied charge transfer plasmons in separate and linked dimers of closed-shell electron clusters of 8 and 138 electrons using time-dependent density functional theory. The simple model clusters enable the systematic study of the charge transfer phenomenon from the electronic perspective. To identify the charge transfer plasmons, we have developed an index, the charge transfer ratio, for quantifying the charge transfer nature of the excitations. In addition, we analyze the induced transition density and the electron transitions contributing to the dipole moment at the charge transfer plasmon energies. Our results show that the optical response of the dimers is very sensitive to changes in the intercluster separation and in the width of the linking channel, with charge transfer plasmon peaks appearing at low energies for dimers with linking or sufficient electron cloud overlap.