As mentioned in the previous chapter, any defect (such as dislocation or the impurity atom) on the metal surface gives rise to the so-called Friedel oscillations, which are defined differently, depending on the context. This phenomenon appears in various fields, including low-frequency plasmonics, many-body theory, a few fields in modern chemistry, and others. For instance, the authors of Ref. consider a semi-infinite homogenous 1D noninteracting gas for which, due to the existence of the surface (imposed as the vanishing of the wavefunction at the point x = 0, as its model potential is presented in Fig. ), they obtained the Friedel oscillations directed towards the interior of the bulk (see Fig. ). There were no realized attempts to make the full 3D Friedel oscillation on a surface theory happen. Originally, this concept was introduced due to the existing question about the distribution of the screening charge. It was long before noticed that two separated electric charges exert lower force upon each other in metal or electrolyte rather than in a vacuum. The classical argument was that by using the Poisson equation, we have the relation between the electric potential V (r) and the screening charge ϱ(r) given as