CRYSTAL STRUCTURE DETERMINATION FROM POWDER DIFFRACTION DATA

摘要

A new software package to determine crystal structures from experimental powder diffraction data, called Powder Solve, is presented. The technique is of significant industrial interest, as many compounds cannot be crystallised as single crystals large enough for single crystal X-ray diffraction techniques – it is often only possible to obtain a crystalline powder. Powder Solve combines Monte Carlo simulated annealing search methods with rigid-body Rietveld refinement tools to determine the crystal structure and refine it against the experimental powder diffraction data. The agreement between simulated and experimental data (expressed by the fullprofile R-factor Rwp) is used to guide the search. For optimal performance, lattice dimensions, peak-shape variables and background parameters are accurately determined prior to the structure solution step. The application of Powder Solve to the determination of the structures of 14 molecular crystals with up to 18 variable degrees of freedom is presented.