W0177

New Approaches To Twinned Data Processing. M. Ruf, J. Chambers, J. Kaercher, Bruker Advanced X-ray Solutions, Madison, WI, U.S.A.

With the introduction of CCD detectors the recognition of diffraction patterns from twinned crystals became much easier. Problems with indexing such patterns are much more obvious with the visual feedback from instant diffraction images. The arising interest in the crystallographic community for handling such cases provided a stimulus for the development of algorithms and software packages capable of visualizing reflections in the undistorted reciprocal space, automatic indexing and data integration. Over the years sophisticated tools were developed to unravel the tangled reciprocal lattices of twins.

Until recently Bruker’s GEMINI was the state of the art tool for automated indexing and data processing of integrated data from twinned crystals. It used intensity data from SAINT derived by independent integrations for each component of the twin. GEMINI then provided a rather crude correction for interferring reflections. The methods of correcting for overlapping reflections were not perfect, but allowed in many cases the determination of a structure acceptable for publication. Another shortfall was that these methods did not allow scaling and absorption correction.

We will present new methods for better treatment of twinned data during integration, scaling and absorption correction. An enhanced version of SAINT allows the simultanous integration of Bragg intensities from all twin components. SAINT deconvolutes overlapping reflections estimating individual intensities from their degree of overlap. Special HKL intensity files are generated which need to be processed with TWINABS for scaling and absorption correction. TWINABS generates HKL files for structure solution and subsequent structure refinement.

Results from processing twinned data using SAINT and TWINABS will be compared with methods previously available. A new graphical user interface to SAINT will be presented providing extensive graphical feedback about the integration process of twins.