P-RISCON - A REAL-SPACE SCAVENGER FOR CRYSTAL-STRUCTURE DETERMINATIONFROM POWDER DIFFRACTION DATA

A computer program, P-RISCON, has been designed with the aim of findin g the location and orientation of one or more independent fragments of known geometry in the unit cell from low-angle X-ray powder diffracti on data only, provided that lattice parameters, space group and a set of integrated intensities are known. A 3D translational search is perf ormed and, if required, rotations of each model about three orthogonal axes are applied, seeking the best match between observed and calcula ted data. No arbitrary partitioning of the intensity of severely overl apping reflections is required as the integrated intensity of a multip let can be used as a single observation, thereby introducing very litt le error in its estimated value. A number of (known) test structures h ave been solved by this method.