Crystal structure solution and prediction via global and local optimization

Simulations machinery broadly available today allows direct-space solutions of crystal structures based on high quality powder diffraction data for systems with up to some 15–20 degrees of freedom. Analogous machinery for predicting new structures is rarely unsuccessful, but has had limited systematic application. The prime challenges for structure solution are for degrees of freedom beyond some 15–20, and for powder diffraction data which is of insufficient quality to allow an unambiguous indexing. In structure prediction, the corresponding issues are (i) enumeration strategies, (ii) collated access to the results of prior predictions, (iii) relating results in some fashion to likelihood of occurrence, encompassing finite temperature issues, and (iv) rational approaches to the synthesis of designed structures. Recent progress in the field has been steady and, while solutions to these key problems are not immediately obvious, the pace of progress over the past 5 years suggests major headway is imminent in a number of these areas.