  Magnetars are neutron stars endowed with surface magnetic fields of the order
of $10^{14}-10^{15}$~G, and with presumably much stronger fields in their
interior. As a result of Landau quantization of electron motion, the
neutron-drip transition in the crust of a magnetar is shifted to either higher
or lower densities depending on the magnetic field strength. The impact of
nuclear uncertainties is explored considering the recent series of
Brussels-Montreal microscopic nuclear mass models. All these models are based
on the Hartree-Fock-Bogoliubov method with generalized Skyrme functionals. They
differ in their predictions for the symmetry energy coefficient at saturation,
and for the stiffness of the neutron-matter equation of state. For comparison,
we have also considered the very accurate but more phenomenological model of
Duflo and Zuker. Although the equilibrium composition of the crust of a
magnetar and the onset of neutron emission are found to be model dependent, the
quantum oscillations of the threshold density are essentially universal.
