Novel Structural Motifs in Clusters of Dipolar Spheres: Knots, Links and   Coils
  We present the structures of putative global potential energy minima for clusters bound by the Stockmayer (Lennard-Jones plus point dipole) potential. A rich variety of structures is revealed as the cluster size and dipole strength are varied. Most remarkable are groups of closed-loop structures with the topology of knots and links. Despite the large number of possibilities, energetically optimal structures exhibit only a few such topologies. 
Mark A. Miller and David J. Wales