  A static microscopic study of potential-energy surfaces within the
Skyrme-Hartree-Fock-plus-BCS model is carried out for the 256Fm and 258Fm
isotopes with the goal of deducing some properties of spontaneous fission. The
calculated fission modes are found to be in agreement with the experimentaly
observed asymmetric-to-symmetric transition in the fragment-mass distributions
and with the high- and low-total-kinetic-energy modes experimentally observed
in 258Fm. Most of the results are similar to those obtained in
macroscopic-microscopic models as well as in recent Hartree-Fock-Bogolyubov
calculations with the Gogny interaction, with a few differences in their
interpretations. In particular an alternative explanation is proposed for the
low-energy fission mode of 258Fm.
