Patterns and barriers for fission of charged small metal clusters

Asymmetric fission of small doubly-charged sodium clusters, investigated via a local-spin-density molecular-dynamics method, is shown to occur predominantly via ${\mathrm{Na}}_{\mathit{n}}^{+2\mathrm{}}$→${\mathrm{Na}}_{\mathit{n}\mathrm{-}3}^{+}$+${\mathrm{Na}}_3^{+}$, for 4≤n≤12. For the smallest cluster (n≤6), fission is barrierless, while fission of larger ones involves barriers. For n=8, 10, and 12 the barriers are 0.16, 0.71, and 0.29 eV, respectively, reflecting the closed-shell stability of the parent with n=10. The fission barriers for n>8 exhibit a double-hump shape, and the dynamics of fission involves a precursor mechanism.