  Both the Coulomb interaction and isospin symmetry breaking (ISB) parts of the
nuclear interaction break the isospin symmetry in atomic nuclei. Effects of
these two kinds of interaction on properties of atomic nuclei, especially, the
mass difference of mirror nuclei and the neutron-skin thickness of $ N = Z $
and $ N \ne Z $ nuclei, are discussed. It is found that corrections to the
Hartree-Fock-Slater approximation for the Coulomb interaction negligibly affect
the neutron-skin thickness, while the charge-symmetry breaking term originating
from the strong interaction might affect it non-negligibly. According to our
calculations, the ISB terms other than the Coulomb interaction affect the
estimation of the density dependence of the symmetry energy, $ L $, by about $
0 $--$ 12 \, \mathrm{MeV} $ using the correlation with the neutron-skin
thickness.
