  The ground-state properties of neutron-rich exotic Na and Mg isotopes with
even numbers of neutrons, N, are studied up to driplines. The shell-model
calculations with an ab initio effective nucleon-nucleon interaction reported
in [Tsunoda, Otsuka, Takayanagi et al., Nature 587, 66 (2020)] are extended to
observables such as magnetic dipole and electric quadrupole moments, and charge
and matter radii. Good agreements with experimental data are found, and
predictions are shown up to driplines. A prescription to extract the
deformation parameters for the eigenstates of Monte Carlo Shell Model is
presented, and the obtained values are used to calculate charge and matter
radii. The increase of these radii from the Droplet model is described as the
consequences of the varying deformation of the surface and the growing neutron
excitations or occupations in the pf shell, consistently with the dripline
mechanism presented in the above reference. The neutron skin thickness is shown
to be about 0.1 fm for N=20, which can be compared to the value for 208Pb in an
A1/3 scaling. The relation of the neutron skin thickness to the electromagnetic
moments is discussed for an exotic nucleus, 31Na.
