  In this Letter, we investigate the variation of endohedral A@CN potential due
to addition at the center of it a positive charge, for example, in the process
of atom A photoionization. Using a reasonable model to describe the fullerenes
shell, we managed to calculate the variation that is a consequence of the
monopole polarization of CN shell. We analyze model potentials with flat and
non-flat bottoms and demonstrate that the phenomenological potentials that
properly simulates the C60 shell potential should belong to a family of
potentials with a non-flat bottom. As concrete example, we use the
Lorentz-bubble model potential. By varying the thickness of this potential, we
describe the various degrees of the monopole polarization of the C60 shell by
positive electric charge in the center of the shell. We calculated the
photoionization cross-sections of He, Ar and Xe atoms located at the center of
C60 shell with and without taking into account accompanying this process
monopole polarization of the fullerenes shell. Unexpectedly, we found that the
monopole polarization do not affect the photoionization cross sections of these
endohedral atoms.
