VRML AS A TOOL FOR EXPLORING COMPLEX STRUCTURES. A. Le Bail, Laboratoire des Fluorures, URA CNRS 449, Universit du Maine, 72017 Le Mans, France.

Exploring a crystal structure from the inside and really understanding it: the Virtual Reality Modelling Language (1) allows this and much more. Simple applications can readily be produced without specialist knowledge. Use your favourite drawing program, decide what you would like to see (select atoms), convert your data into a standard .wrl file and then view the result on almost any platform. A PDB (Protein Data Bank) to VRML converter already exists (2).The whole operation (apart from PDB2VRML which is UNIX only) can even be carried out on just a fast PC although graphics workstations improve productivity. For inorganic structures an excellent procedure is to convert SHELX .ins into .pdb files using BABEL (3), select those atoms suitable for the display required, verify the result with RASMOL (4) and finally create automatically the .wrl file with PDB2VRML. A change in the pre-defined radius and colors can be undertaken by editing the ASCII .wrl file. A more direct builder is xtal-3d (5) for UNIX platforms, a PC adaptation being planned.

The most exciting moment during the course of a crystal structure determination occurs when enough atomic positions are known to be able to draw at least a partial model. The less exciting is when it is realized that the structure is so complex that it will be necessary to build a real 3D paper (or ball and stick) model in order to be sure that nothing has been overlooked in the structure description. VRML can help one to do almost the whole job in a few minutes starting from standard drawing files. Visual applications are limited only by ones own imagination. For the specialist it is feasible to create 3D crystallographic scenarios, calling objects stored at different URLs on the net. The real usefulness to crystallography of 3D mark-up is an open question.

1. J.C. Hardenbergh, http://www.oki.com/vrml/VRML_FAQ.html

2. H.Vollhardt, http://ws05.pc.chemie.th-darmstadt.de/vrml/pdb2vrml.html

3. P. Walters & M. Stahl, http://mercury.aichem.arizona.edu/babel.html

4. R. Sayle, ftp://ftp.dcs.ed.ac.uk/pub/rasmol

5. M. Hewat, http://193.49.43.3/dif/3D_crystals.html