Computational Prediction of Crystal Structures and Polymorphs

Venue: Seminar Room Fisica teorica - 2nd floor

At: 11.00

• E. Schneider - New York University

Abstract:
Prediction and exploration of possible polymorphism in organic crystals are of great importance for industries ranging from organic electronics to pharmaceuticals to high-energy materials.
In the last 20 years, great effort has been made in the development of computational methodologies to predict molecular crystal structures. However, theoretical prediction of molecular crystal structures remains a difficult task even with today’s sophisticated models and computing resources.
The crystal structure prediction procedure developed by our group starts with on random structure generation using the UPACK software package to obtain a set of possible crystal candidates. Then, we apply different molecular dynamics techniques (NPT-flexible simulations, crystal adiabatic free energy dynamics, metadynamics, etc) to check the thermal stability of each structure, ranking the list of crystal candidates based on their lattice energy and free energy, and to explore the possibility of polymorphism.

We applied this procedure to benzene and naphthalene, successfully predicting the most stable crystal structures at atmospheric pressure and exploring the relative Gibbs free energies of predicted polymorphs at high pressures. Further, we found that mixed structures, which typically cannot be discovered by standard crystal structure prediction methods, are prevalent in the solid forms of these compounds at high pressure.
In addition, we participated in the sixth blind test for organic crystal structure prediction, obtaining the experimental crystal structure for the rigid molecule. The use of molecular dynamics simulations allowed us to include thermal effects in our prediction obtaining the best match between theoretical and experimental structures.
We also combined our computational crystal structure prediction algorithm and experimental X-ray powder diffraction to solve the crystal structure of four new metastable coumarin polymorphs grown from the melt.