P-RISCON: a real-space scavenger for crystal structure determination from powder diffraction data

A computer program, P-RISCON, has been designed with the aim of finding the location and orientation of one or more independent fragments of known geometry in the unit cell from low-angle X-ray powder diffraction data only, provided that lattice parameters, space group and a set of integrated intensities are known. A 3D translational search is performed and, if required, rotations of each model about three orthogonal axes are applied, seeking the best match between observed and calculated data. No arbitrary partitioning of the intensity of severely overlapping reflections is required as the integrated intensity of a multiplet can be used as a single observation, thereby introducing very little error in its estimated value. A number of (known) test structures have been solved by this method.