  The ground-state deformations of the Ge isotopes are investigated in the
framework of Gogny-Hartree-Fock-Bogoliubov (HFB) and Skyrme Hartree-Fock plus
pairing in the BCS approximation. Five different Skyrme parametrizations are
used to explore the influence of different effective masses and spin-orbit
models. There is generally good agreement for binding energies and deformations
(total quadrupole moment, triaxiality) with experimental data where available
(i.e., in the valley of stability). All calculations agree in predicting a
strong tendency for triaxial shapes in the Ge isotopes with only a few
exceptions due to neutron (sub-)shell closures. The frequent occurrence of
energetically very close shape isomers indicates that the underlying
deformation energy landscape is very soft. The general triaxial softness of the
Ge isotopes is demonstrated in the fully triaxial potential energy surface. The
differences between the forces play an increasing role with increasing neutron
number. This concerns particularly the influence of the spin-orbit model, which
has a visible effect on the trend of binding energies towards the drip line.
Different effective mass plays an important role in predicting the quadrupole
and triaxial deformations. The pairing strength only weakly affects binding
energies and total quadrupole deformations, but considerably influences
triaxiality.
