Crystallographers

Abstract

The category Computer Program Abstracts provides a rapid means of communicating up-to-date information concerning both new programs or systems and significant updates to existing ones. Following normal submission, a Computer Program Abstract will be reviewed by one or two members of the IUCr Appl. Cryst. (1985). 18, t89-t90].J. AppL Cryst. (1996) (Received 7 Febrary 1996; accepted 9 April 1996) The crystallographic problem: The use of computer programs has considerably simplified the determination of unknown crystal orientation, avoiding the classical method using stereographic projection and Wulff nets. Simulations may also be useful for teaching purposes.Since the first simulation of a Laue pattern by KrahI-Urban, Butz & Preuss (1973), many programs have been written for the simulation and/or indexation of Laue diagrams. Some of them are referenced by Marin, Cintas & Di~guez (1994).Up to now, it seems that no modern general program dedicated to the processing of diffraction data has been available on UNIX workstations, except the LAUEGEN package of Campbell (1995). However, LAUEGEN is a large program, requiring a lot of disk space, involved in a suite whose aim is the computation of integrated intensities with a view to structure resolution, while LAUEX is only a small simulation/indexation program for everyday work. Method of solution:LAUEX is a userfriendly program, with an X Window graphical interface. The user enters data in the menus and chooses options by clicking on buttons or moving sliders with the mouse. The data may be saved for later use.LAUEX performs the following tasks: (i) Simulation of a Laue diagram, from knowledge of the orientation of the crystal, the cell parameters and the position © 1996 International Union of Crystallography Printed in Great Britain -all rights reserved of the detector. Note that LAUEX is not limited to the transmission and reflection cases, but that the position of the detector may be located anywhere on a sphere centred on the crystal. This feature has been introduced especially for work carried out at a synchrotron. If the structure of the crystal is known, the program may evaluate the intensities of the Laue spots and draws them as spots whose size is proportional to their intensity. The parameters taken into account for this computation are those described by Preuss (1979) (except for the crystal shape), plus the response curve of the detector.(ii) Indexation of an experimental Laue diagram, by the knowledge of the cell parameters and the position of a number of spots of low index. The indexation procedure has been suggested by Riquet & Bonnet (1979) and has already been used by Laugier & Filhol (1983).(iii) Alignment of a crystallographic direction along an axis of the apparatus (usually the one pointing towards the X-ray source), or rotation of the crystal.(iv) Storing of the simulated diagram as a PostScript file, or printing directly to a laser printer.On-line help is available if a World Wide Web (WWW) browser is installed on the machine.Software enviro...