**6. Outlook**

Any novel approach, including the CEE model, can be truly evaluated by a benefit from its practical application. By an example of the graphite based materials, the chapter has shown how a confluence of the XPS and DFT data can provide additional information on chemical behavior, local geometry and state of the embedded Br<sup>2</sup> molecule and of the other atoms in a sample. A similar treatment can be useful in the field of surface engineering as well, because just a deep knowledge on chemical behavior of a sample can disclose the mechanism and dynamics of its wear performance, thus facilitating the development of advanced materials. The valence band of chemically bound atoms is insensitive to a photoelectron, whose energy it uses for the CEE transition. Then, in the case of the multicomponent materials, agreement or disagreement between energy losses in the XPS spectra of some atoms can be a descriptor of the presence or absence of chemical bonding between these atoms in a sample [17, 19, 22]. Moreover, the state of any component can be traced through change or invariability of the satellites in its XPS spectra, obtained in the course of external influence, thus revealing a wear performance of the material. In case of a "simple" material, the reliable structural data can be used as starting conditions for the appropriate DFT run, which gives comprehensive information on a sample at the atomic level [16, 18]. Extensive use and practice of the XPS and DFT techniques make the CEE analysis easily accessible.

CEE control in a coordinated XPS and DFT study is characterized by the following obvious, verified, and hidden resources.

