  Fission of metastable charged univalent metal clusters has been studied on
example of Na_{10}^{2+} and Na_{18}^{2+} clusters by means of density
functional theory methods. Energetics of the process, i.e. dissociation
energies and fission barriers, as well as its dynamics, i.e. fission pathways,
have been analyzed. The dissociation energies and fission barriers have been
calculated for the full range of fission channels for the Na_{10}^{2+} cluster.
The impact of cluster structure on the fission process has been elucidated. The
calculations show that the geometry of the smaller fragment and geometry of its
immediate neighborhood in the larger fragment play a leading role in defining
the fission barrier height. The present study demonstrates importance of
rearrangement of the cluster structure during fission. It may include forming a
neck between the two fragments or fissioning via another isomer state of the
parent cluster; examples of such processes are given. For several low-lying
isomers of Na_{10}^{2+} cluster the potential barriers for transitions between
these isomer states are calculated and compared with the corresponding fission
barriers. These data suggest that there is a competition between "direct"
fission and fission going via intermediate isomer states of the parent cluster.
An impact of the cluster geometry on the change of the system's entropy due to
fission is also discussed.
