Fission of doubly ionized calcium clusters

Cluster ions, Ca N + and Ca N 2 + , containing up to N = 8 atoms are studied within density functional theory. Ground and first excited states, and ionization energies are reported for all sizes. At zero temperature Ca 3 2 + and Ca 4 2 + are linear, whereas Ca 5 2 + through Ca 7 2 + undergo structural transitions from 3D-configurations into linear ions below 600 K. As a consequence, fission that occurs above 600 K starts from linear configurations. Ca 8 2 + has an hexagonal bipyramidal structure. The preferred fission channels are Ca N 2 + → Ca + + Ca N - 1 + with fission barriers smaller than the evaporation energy up to Ca 7 2 + . However, Ca 8 2 + presents a large fission barrier and would rather evaporate one atom than undergo fission.