Jul 312010

CRYSTALS v14.11 is available as a beta-test.

Many small changes in Regularise Replace thanks to a CRYSTALS workshop in Toulouse organised by Carine Duhayon and Laure Vendier.

Cif generator now properly includes esds on refined hydrogen bonds, has incrreased figure-fields for cell parameters, and appends constraint and restraint information as _iucr_ data items at end of cif.

Improved scaling of difference Pattersons – see forthcoming paper by Flack, Sadki, Thompson & Watkin.

Absolute configuration routine (based on PLATON with Ton Spek’s permission) extended to provide more diagnostics and additional data to be re-input as absolute-structure strengthening restraints (see paper by Flack et al. above).

Error tracking for “USE” files has been improved.

Collaboration with Ernesto Mesto (Dipartimento Geomineralogico – Università degli Studi di Bari) uncovered over-sights in the original 1979 code, which lost contributions when a twin component fell onto a centring absence. Difference maps with twinned data now seem to reveal hydrogen atoms very reliably.

Apr 012002

J. Appl. Cryst. (2002), 35, 168-174.    [ doi:10.1107/S0021889802000249 ]

Although non-merohedrally twinned crystal structures can normally be solved without difficulty, problems usually arise during refinement. Careful analysis of poorly fitting data reveals that they belong predominantly to certain distinct zones in which |Fo|2 is systematically larger than |Fc|2. In the computer program ROTAX, a set of data with the largest values of (|Fo2| – |Fc2|)/u(|Fo2|) is identified and their indices transformed by rotations or roto-inversions about possible direct- and reciprocal-lattice directions. Matrices that transform the indices of the poorly fitting data to integers are identified as possible twin laws.