POWDIS and POWUTL - PC programs for the display and simulation of X-ray powder patterns

The crystallographic problem: X-ray powder patterns can provide a useful check on the relationship between the phase of a crystal chosen for single-crystal work and the phase of the bulk sample. This software allows the direct comparison of single-crystal and powder data and provides facilities for display, plotting and simulation of powder patterns. Method of solution: Two programs POWDIS and POWUTL are provided for the display of powder data and for the manipulation of data files. POWDIS can display and plot powder spectra. The spectra may be marked, integrated and plotted. A zoom facility is provided and spectra may be displayed together for comparison (Fig. 1). The display may be in d space or 29 units and the displayed radiation wavelength can be altered. One useful application of this facility is that spectra obtained with Co radiation (λ = 1.79 Å) which show excellent resolution on organic pharmaceutical samples can be replotted for comparison with more conventional Cu data. The powder patterns in Fig. 1 are, in the upper trace, the observed pattern for a nickel salicylaldimene complex cocrystallized with CsNO₃ in a supramolecular assembly and, in the lower pattern, that computed for the Cs and Ni atoms only. This arrangement of metal atoms was easily detected in powder patterns of related assemblies. The POWUTL program can: (i) convert SHELX.hkl files to powder patterns; (ii) perform simple digital filtering (to increase or decrease resolution); (iii) convert to and from Crystallographic Information File (CIF) format; (iv) change wavelength and maintain digitization; and (v) generate powder data from SHELX .ins files. Option (v) requires the use of SHELX-93 (Sheldrick, 1993). Hardware environment: The program requires at least a 386/387, DOS5 and 4 Mbytes of RAM. Availability: The programs and test data are available via the WWW (http://balor.ucg.ie/cryst/software.htm) or on floppy disk from the authors.