Richard B. McClurg, Principal Investigator

Intermolecular Potentials Inferred From Crystallographic Data

Prediction of molecular crystal structures is extraordinarily difficult due to the extreme sensitivity of the free energy surface to small changes in the intermolecular potential. This research group is using this sensitivity to their advantage by inverting the problem. Given observed crystal structures, they are working towards inferring constraints on intermolecular potentials that are consistent with the observations. Due to the extremely sensitive dependence of crystal structure on intermolecular potentials, these constraints define a very small family of candidate potentials.

As a starting point, this group is modeling tetrahedral molecules that form “plastic” crystals. Plastic crystals are orientationally disordered at high temperature, but have ordered phases at low temperature. The group has used the Cambridge Structural Database to identify structures and phase transitions for a group of tetrahedral plastic crystals (e.g., carbon tetrabromide, adamantine, silane, etc.), which will serve as a test case. They are modeling the intermolecular potential using a generic Fourier expansion of orthogonal symmetry- adapted rotator functions are developing methods for inferring constraints on the Fourier coefficients using the structural and phase transition information. This is part of an ongoing effort to establish the relationship between intermolecular potential and crystal structure.

Research Group

J. Brandon Keith, Graduate Student Researcher