ABSTRACT
This chapter provides the full information from random-phase approximation calculations, for example, the lowest plasmon frequency among several systems and the most difficult observations using electron energy loss spectroscopy (EELS) and optical spectroscopies. The dominating Coulomb screenings might belong to the perpendicular momentum transfer; furthermore, there is low 2D free carrier density. The simple hexagonal graphite exhibits parallel and perpendicular collective oscillations relative to the graphitic planes, with frequency higher than 0.5 eV. The high-, middle-, and low-frequency plasmon modes in Bernal graphite have been measured and identified by optical spectroscopies and EELS. Bernal graphite has two layers and four carbon atoms in a primitive unit cell, in which the A and B sublattices on two layers will experience different chemical environments. The lower-symmetry rhombohedral graphite has the lowest free electron/hole density among three kinds of well-behaved stacking configurations, so that it is expected to be relatively difficult in creating low-frequency collective excitations.
