Journal of Chemical Physics, Vol.109, No.9, 3596-3599, 1998
Orientational order-disorder phase transitions in plastic molecular clusters : Projection of three-dimensional distributions onto a two-dimensional surface
In addition to the traditional methods of identification of order-disorder transformations in nanoscale clusters containing highly symmetrical molecules, we have developed a simple projection method to recognize such transformations. The three-dimensional orientation distributions of the molecules are projected onto a two-dimensional spherical surface without any loss of information. We have applied the method in the analysis of the phase changes of clusters containing up to 180 tellurium hexafluoride molecules. The molecular configurations are generated by constant energy molecular dynamics simulations of the thermal history of free clusters. We observe two successive transitions as the clusters cool from their melting point. The projection method clearly reveals the mechanism of the structural transformations in the studied clusters : the orientation order of the molecular axes at low temperatures is accompanied by lattice distortion.