Size-induced melting and reentrant freezing in fullerene-doped helium clusters

Abstract

The structural and dynamical stabilities of C${}_{60}^{+}$He${}_{N}$ clusters are theoretically investigated using global optimization and path-integral simulation methods. Up to $N=32$, the fullerene ion traps the helium atoms onto sixfold and fivefold faces, strongly enough to negate vibrational delocalization. Above this size, geometric frustration takes over and the clusters grow as a thin but homogeneous liquid layer. However, as their size reaches 60 atoms, corrugation barriers are suppressed and the cluster is again rigidlike. Additional fluid layers are predicted to arise above 72 atoms.