A 3D crystal structure VRML generator

6 October 1997

xtal-3d is an application to generate VRML files representing 3D crystal structures such as the simple perovskite structure above: you do not usually need to download xtal-3d since you can use the WWW version. But you will first want to see some examples in our 3D crystal structure gallery.

xtal-3d was written by Marcus Hewat during an (unpaid) 1994 student vacation job at ILL Grenoble. It was originally written for Silicon Graphics' Inventor format, which later became VRML-1, but now runs on many other kinds of computer (PC, Macintosh and Unix). The WWW version is used with ICSD for WWW, our inorganic structure database. Actually the application is most commonly used as a simple command-line program called xtal-3c while xtal-3d usually includes the GUI interface. For more 3D computer graphics see Marcus Hewat's WWW pages.

xtal-3c was made to be used with a minimum of data or instruction. Typing just xtal-3c will tell you how to use the program, and xtal-3c x will generate a ¶sample VRML structure file as illustrated on the left (click the image to obtain it full size). The program then waits for instructions, which can be as simple as g to draw the structure: a list of instructions is obtained by typing ? or a carriage return. Note how ellipsoids have been drawn to illustrate thermal vibration amlitudes, but of course sperical atoms can also be chosen.

By default xtal-3c will look for bonds between the last two types of atoms in the structure file, but it can be told instead to use bonds between At1-X and At2-Y with instructions At1-X At2-Y. By default it will try to construct polyhedrae using a list of atom radii and colours kept in file xtal-3d.at: this file can be edited by the user, but the user can also change these parameters on the fly by issuing instructions such as At-X 1,1,0 to draw yellow atoms and polyhedrae around At. Instead of polyhedrae (command p) ¶cylindrical c or simple stick s bonds can be drawn, or some combination.

Atoms can be drawn at full size (space filling), as small spheres, or invisible. Atoms can be labelled, the unit cell drawn as a transparent or semi-transparent box etc., and of course ¶multiple unit cells can be added in any direction.

If you are using one of the graphic user interfaces or the WWW version all this becomes obvious, but the basic commands can be entered if prefered, or the commands can be attached directly to the structure file.

Finally, you might like to see some examples of 3D VRML structure drawings produced by xtal-3d.

Please report any problems with xtal-3d to hewat@ill.fr.