The analysis of self-consistency and proton-neutron interaction effects in
the buildup of differential charge radii has been carried out in covariant
density functional theoretical calculations without pairing interaction. Two
configurations of the 218Pb nucleus, generated by the occupation of the
neutron 1i11/2β and 2g9/2β subshells, are compared with the ground
state configuration in 208Pb. The interaction of added neutron(s) and the
protons forming the Z=82 proton core is responsible for a major contribution
to the buildup of differential charge radii. It depends on the overlaps of
proton and neutron wave functions and leads to a redistribution of
single-particle density of occupied proton states which in turn modifies the
charge radii. Self-consistency effects affecting the shape of proton potential,
total proton densities and the energies of the single-particle proton states
provide only secondary contribution to differential charge radii. The buildup
of differential charge radii is a combination of single-particle and collective
phenomena. The former is due to proton-neutron interaction, the impact of which
is state dependent, and the latter reflects the fact that all occupied proton
single-particle states contribute to this process. The neglect of either one of
these aspects of the process by ignoring proton-neutron interaction and
self-consistency effects as it is done in macroscopic+microscopic approach or
by introducing the core as in spherical shell model introduces uncontrollable
errors and restricts the applicability of such approaches to the description of
differential charge radii.Comment: 14 pages, 8 figures, submitted to Physical Review