1. Workshop on Dispersion Interactions and DFT August 1-3, 2012 Dr. James Parker Program Manager, Molecular Structure and Dynamics Chemical Sciences Division U.S. Army Research Office Research Triangle Park, North Carolina

2. Workshop Goal To identify new, innovative methods to include quantitative dispersion interactions (predictive) in DFT calculations without compromising cost or accuracy

3. Molecular Co-Crystal Design Physical and Chemical Properties of Molecular Crystals are Governed by Structure: Polymorphism white, red, and black phosphorus Formwhiteredblack Symmetry bccamorphous ortho- rhombic Reactivity pyro- phoric stable; used in matches low Density 1.8282.342.69 Bandgap 2.10.34 Ref. Index 1.82442.4 Properties of Phosphorus

4. Recrystallization (homomeric) or co-crystallization (heteromeric) Recrystallization vs. Co-crystallization Molecular Co-Crystal Design

5. Molecular Co-Crystals  Offers potential to design molecular solid state structures with desired physical and chemical properties  Relies on understanding of molecular interactions in the context of crystal packing Research Barriers  Synthesis: lack of quantitative predictive ability for developing reliable, effective, and versatile synthetic methods (synthons) for the directed assembly of heteromeric co-crystals  Theory: historically, cannot predict accurate crystal structures from a molecular structure.

6. Prismatic habits of TNT:CL-20 co- crystal. Scale bar is 500 μm. Scientific Opportunity: TNT:CL-20 co-crystals are formed in the laboratory  (Matzger) Angew. Chem. 2011, 123, 9122-5.  New energetic co-crystal with 81% energy density of CL-20 with only 66% Cl-20 by mass  Density of co-crystal is 1.91; compare to TNT density of 1.70 and CL-20 density of 2.08  Impact sensitivity of the co-crystal is a factor of 2 less than CL-20 (drop test method)  combines stability of TNT with density and power of CL-20 in one homogeneous material Molecular Co-Crystal Design TNTCL-20 Interactions between TNT and CL-20 in the co-crystal.

7. Scientific Opportunity: New efficient computational chemistry method, SAPT(DFT), can quantitatively predict molecular crystal structures  (Szalewicz) Phys. Chem. Chem. Phys. 2011, 13, 16629-36. The predicted FOX-7 unit cell configuration superimposed onto the experimental structure Molecular Co-Crystal Design a b c Comparison of experimental and predicted crystallographic parameters  Differences are less than 1 percent!

8. Scientific Opportunities  Co-crystal formation of TNT:CL-20 has been directed in the laboratory.  Predictive computational tools are available for molecular crystal design. Impact Areas  molecular crystal properties  novel energetic materials  supramolecular chemistry  crystal engineering  materials science Molecular Co-Crystal Design Intermolecular interactions within the TNT:CL-20 co-crystal