N-DIMENSIONAL SPACE GROUP SYMMETRY ON THE WEB. A.Thiers, H.de Hilster, M.Ephraim, CAOS/CAMM Center, University of Nijmegen Toernooiveld 1 6525 ED Nijmegen The Netherlands

N-dimensional space groups play an important role in the description of incommensurate crystals, like quasi crystals and incommensurately modulated crystals. These types of materials can be looked upon as the intersection of the physical space with a higher-dimensional lattice periodic structure. The dimension of the latter is equal to the number of indices needed for the diffraction pattern.

The purpose of the programme is to provide information about the space groups of arbitrary dimensions. It allows for manipulation and inspection of the groups, e.g. subgroups, Wyckoff positions and systematic extinctions. Visualization of space groups, e.g. of the general or special positions or the space group elements, is done using VRML (Virtual Reality Modelling Language).

The number of space groups increases rapidly when one goes to higher dimensions. This makes it not feasible to present the information as a printed volume. The information, generated from data (generating elements) in a data base, or from user supplied data comprises the space groups, the symmetry elements, the Wyckoff positions and the general and special extinctions. The goal is to show all data present in the existing tables for 2 and 3 dimensions, with the benefit of choosing an arbitrary origin and setting.

The user computer interaction is realized using FORMs and POSTs sent between a special HTTP daemon and the user's WWW browser, giving the interactive feel of a local computer programme. The FORM interface features buttons of all kinds, input fields, checkboxes and selection menus.