  Accurate knowledge of fission fragment yields is an essential ingredient of
numerous applications ranging from the formation of elements in the r-process
to fuel cycle optimization for nuclear energy. The need for a predictive theory
applicable where no data is available is an incentive to develop a fully
microscopic approach to fission dynamics. In this work, we calculate the
pre-neutron emission charge and mass distributions of the fission fragments
formed in the neutron-induced fission of 239Pu using a microscopic method based
on nuclear energy density functional (EDF) method, where large amplitude
collective motion is treated adiabatically using the time dependent generator
coordinate method (TDGCM) under the Gaussian overlap approximation (GOA).
Fission fragment distributions are extracted from the flux of the collective
wave packet through the scission line. We find that the main characteristics of
the fission charge and mass distributions can be well reproduced by existing
energy functionals even in two-dimensional collective spaces. Theory and
experiment agree typically within 2 mass units for the position of the
asymmetric peak. As expected, calculations are sensitive to the structure of
the initial state and the prescription for the collective inertia. We emphasize
that results are also sensitive to the continuity of the collective landscape
near scission. Our analysis confirms that the adiabatic approximation provides
an effective scheme to compute fission fragment yields. It also suggests that,
at least in the framework of nuclear DFT, three-dimensional collective spaces
may be a prerequisite to reach 10% accuracy in predicting pre-neutron emission
fission fragment yields.
