Numerical Evidence of an Embryonic Orientational Phase Transition in Small Nitrogen Clusters

Using molecular dynamics simulation we provide some evidence of an embryonic solid-solid phase transition in (N₂{)}₁₃$ cluster. This transition, as characterized in terms of the underlying potential energy surface, is accompanied by the release of the molecular orientational degree of freedom. This transition is also observed in (N₂{)}₅₅$ but not in (C${O}₂)₁₃. It is presumably a finite size analog of the bulk rigid to plastic phase transition, which is known to occur in solid N₂ but not in CO₂.