Macromolecular X-ray crystal structure analysis against limited and noisy data
Garib N. Murshudov · Acta Crystallographica Section A Foundations of Crystallography · 2010
Ab-initio crystal structure determination from powder diffraction data became more and more popular in the last 20 years, thanks to the development of effective novel methods and powerful experimental devices. These enhancements enable to solve, often routinely, organic, inorganic and metallo-organic crystal structures, even if not always they ensure the success because of unavoidable problems like peak overlap, preferred orientation and/or background estimation. EXPO2010, the evolution of EXPO2009 [1], is a package able to perform all the steps of the ab-initio structure determination process: indexing; space group determination; estimation of the reflection integrated intensities; structure solution (both in reciprocal and direct space) and structure refinement. Special procedures make more straightforward the crystal structure solution process, especially in case of low resolution data and/or organic compounds. They are: 1) a new figure of merit for identifying the correct cell among a set of plausible solutions; 2) new methods, working in direct and reciprocal space, able to correct the truncation effects on the electron density; 3) direct space techniques (simulated annealing and hybrid approach). Among the new algorithms implemented in EXPO2010 we quote: