Ground state energies are obtained using the unrestricted Hartree Fock method
for up to four interacting electrons parabolically confined in a quantum dot
subject to a magnetic field. Restoring spin and rotational symmetries we
recover Hund first rule. With increasing magnetic field, crossovers between
ground states with different quantum numbers are found for fixed electron
number that are not reproduced by the unrestricted Hartree Fock approximation.
These are consistent with the ones obtained with more refined techniques. We
confirm the presence of a spin blockade due to a spin mismatch in the ground
states of three and four electrons.Comment: 16 Pages, 2 figures, accepted for publication on New Journal of
Physic
