Abstract:

In this talk I plan to present a first principles study of the low-energy dielectric response function in bulk and surfaces of several representative materials calculated in the framework of time-dependent density functional theory. In particular the examples of the graphene, intercalated graphite, transition metal dichalcogenides, and Pb are considered. Our calculation results reveal the presence of several kinds of plasmons in the energy range below 10 eV. The presence of these excitation modes is discussed in terms of intra- and inter-band transitions. In particular, appearance of the linear-dispersing low-energy collective electronic modes is interpreted in terms of existence of the energy bands with different velocities at the Fermi surface. Reappearance of some of the mentioned collective modes at large momentum transfers is also analyzed and related to the local crystal field effects.