The propagator of the induced dynamically screened Coulomb interaction 
is calculated for the 
monolayer. The energy-loss rate of a point charge placed near the monolayer is calculated (using the spatial resolution of the 
in the direction perpendicular to the plane) and successfully compared with very recent electron-energy-loss spectroscopy measurements of Hong et al. [ J. Hong et al., Phys. Rev. B 93, 075440 (2016) ]. The induced propagator , compared with its classical analogous propagator, is used to determine the effective dielectric function 
of atomically thick crystals. It is shown that 
extracted from is in good agreement with the dielectric function of the extracted from the ellipsometry measurements. A recently proposed method for calculation of the dielectric tensor in quasi-two-dimensional crystals is used to calculate the parallel 
and perpendicular 
dielectric functions in , which are compared with some previous measurements and calculations.
Vito Despoja, Zoran Rukelj, and Leonardo Marušić