GLOBAL ORIENTATIONAL ORDER IN MODEL POLAR CLUSTERS

Overall rotational anisotropy is found to be generic in compact cluste rs of model dipolar particles. This broken rotational symmetry, or ''g lobal'' orientational order, is pronounced in zero temperature configu rations. It arises from the tendency of dipolar particles to form head -to-tail chains which encircle the cluster, giving rise to a circulati ng pattern. In many cases, the zero temperature arrangement of dipolar particles is chiral. Expansion of the dipole density field in vector spherical harmonics provides order parameters to quantify broken orien tational symmetry, and facilitates analysis of inversion and reflectio n symmetry. Finite temperature simulations of a 13-particle cluster wi th Stockmayer (Lennard-Jones+point dipole) interactions indicates that the global orientational order persists to higher temperatures, even above the point of translational melting. The 13-particle Stockmayer c luster remains orientationally ordered up to the onset of frequent eva poration from the cluster. Ramifications of this effect are discussed.