  We use a fully quantum mechanical approach to analyze the effects of
molecule-scale perturbations on the plasmonic excitations in prototype models
of topological insulators. Strongly localized surface plasmons are present in
the host systems, arising from the topologically non-trivial single-particle
edge states. A numerical evaluation of the RPA equations for the perturbed
systems reveals how the position and the internal electronic structure of the
added molecules affect the degeneracy of the locally confined collective
excitations, i.e., shifting the plasmonic energies of the host system and
changing their spatial charge density profile. In particular, we identify
conditions under which significant charge transfer from the host system to the
added molecules occurs. Furthermore, the induced energy of the perturbed
topological systems due to external electric fields is determined.
