Even though single crystal diffractometry is the method of choice when it comes to crystal structure determination, this approach is frequently impractical because of the difficulties involved in growing single crystals of appropriate size. Powder diffraction patterns are obtained more readily, but for a long time, structure solution from powder data was considered to be a difficult task because of the loss of information that results from the projection of diffraction peaks onto a single dimension. Only in recent years has it been realised that reverse Monte Carlo techniques in conjunction with modern computer hardware offer a straightforward approach to structure solution from powder diffraction data. Using reverse Monte Carlo techniques, huge amounts of trial structures are generated and compared to the experimental data, the structure generation being guided towards the best solution by global search algorithms.

With the advent of professional software for structure solution from powder data, this powerful alternative to single crystal structure determination has now become available to scientists from different backgrounds who are not necessarily specialised in powder diffractometry. Combined with easy-to-use tools for model building and visualisation as well as molecular mechanics calculations, crystal structure solution from powder data by reverse Monte Carlo techniques is becoming a routine task.

At the workshop, participants will have the opportunity to gain hands-on experience with Reflex Plus, a new Powder Diffraction module in the PC based materials modelling environment Materials Studio. Reflex Plus is a complete package for structure determination, providing tools for indexing, Pawley refinement, structure solution and Rietveld refinement. Crystal structures are solved with an improved version of Powder Solve, a state-of-the-art structure solution program that was previously exclusive to members of the Molecular Crystallization Consortium, but that has now been released to the general public. Among other improvements, the latest version of Powder Solve benefits from a more powerful global search algorithm based on parallel tempering and new functionality to solve crystal structures in the presence of preferred orientation.

Working through a set of tutorials and aided by several tutors, participants of the workshop will solve a variety of organic and inorganic crystal structures. In the process, the participants will learn more about powder indexing, Pawley refinement, space group selection, model building, geometry optimisation by force field calculations, structure solution and Rietveld refinement.

For more information, please contact Marcus A. Neumann (mneumann@msi-eu.com).

Structure of akermanite solved with Reflex Plus in Materials Studio.