title: Enhanced efficiency of direct-space structure solution from powder X-ray diffraction data in the case of conformationally flexible molecules.
abstract: A strategy is reported for assessing the feasibility of molecular conformations within direct-space structure-solution calculations of organic molecular crystal structures from powder X-ray diffraction data, focusing in particular on the genetic algorithm technique for structure solution in which fitness is defined as a function of the whole-profile figure-of-merit Rwp. The strategy employs a readily computed distance-based function to assess the feasibility of the molecular conformation in each trial structure generated in the genetic algorithm calculation, and structures considered to have low-feasibility conformations are penalized within the evolutionary process. The strategy is shown to lead to significant improvements in the success rate of structure-solution calculations in the case of flexible molecules with a significant number of conformational degrees of freedom.
authors.affiliation: School of Chemistry, Cardiff University, Park Place, Cardiff, CF10 3AT Wales, UK.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Hanson
authors.forename: Eugene Y
authors.initials: EY
authors.lastname: Cheung
authors.forename: Kenneth D M
authors.initials: KD
authors.lastname: Harris
mesh_terms: D000465:Algorithms; D003460:Crystallization; D008958:Models, Molecular; D008968:Molecular Conformation; D015394:Molecular Structure; D010446:Peptide Fragments / Q000737:chemistry*; D033362:Powder Diffraction; D014961:X-Ray Diffraction
chemical_list: D010446:Peptide Fragments