A generalized scheme for characterizing orientational correlations in condensed phases of high symmetry molecules: SF6 and C60

Simulated datasets, and source code of the applied programs related to the publication appeared in Journal of Molecular Liquids Volume 341, 1 November 2021, 116916 (doi.org/10.1016/j.molliq.2021.116916) The orientational correlation scheme introduced earlier for tetrahedral molecules is extended to being able to classify orientational correlations between pairs of high-symmetry molecules. While in the original algorithm, a given orientation of a pair of tetrahedral molecules is characterized unambiguously by the number of ligand atoms that can be found between two planes that contain each centre and perpendicular to the centre-centre connecting line, in the generalized algorithm, the planes are replaced by cones, whose apex angles are set according to the symmetry of each molecule.

To demonstrate the method's applicability, the octahedral-shaped SF6 molecule is studied in a wide range of phases (gaseous, supercritical fluid, liquid and plastic crystalline) using classical molecular dynamics. By analyzing the orientational correlations, a close-contact region in the first coordination shell and a medium-range order behaviour are identified in the non-crystalline phases. While the former is invariant to changes in the density, the latter showed longer-ranged correlations as density is raised.