TOWARDS A WEB-BASED INTERACTIVE COURSE ON CRYSTALLOGRAPHY

Gervais Chapuis¹ and Wes Hardaker²

¹Institut de cristallographie, Université de Lausanne, 1015 Lausanne, Switzerland
²Information Technology, University of California at Davis, Davis CA 95616, U.S.A

Keywords: Java applets, crystallography teaching, interactive teaching, web application

While teaching the basics of crystallography, the specialist is confronted with the need to use the third dimension to illustrate certain principles such as point symmetry operations, the principles of diffraction by crystals or details of elaborate crystal structures. With the ubiquitous availability of computers (even in lecture halls), crystallographers can take advantage of existing programs in order to illustrate some specific aspects of the field. The immediate problem to face, however, is the choice of which computer platform to purchase. Many interesting applications have been written, but unfortunately no single computer can accommodate all of them.

Fortunately, web-based applications can avoid this serious drawback. The recent introduction of the Java programming language allows platform-independent development of applications which can be directly accessed by anyone utilizing the web. The current versions of the standard browsers are all able to handle these so called "java applets". Java applications can be used to illustrate specific aspects during a lecture. What is perhaps more efficient is the possibility for the student to repeat the demonstrations individually, at his own pace, with a computer linked to the network or from home if a modem is available.

With this universality in mind, we have developed a series of Java applications which illustrate some important concepts of crystallography: point group symmetry, space group symmetry and the elements of crystal diffraction. In point group symmetry operations, the advantage of using a computer model is that we can indeed perform a roto-inversion or, more generally, an improper rotation, which is not possible with a solid model. The (2d-) space group symmetry can be dynamically implemented with a Java applet and the student can be quickly familiarized with the concepts of general and special positions and site symmetry. Any (2d-) structure can be easily constructed in a snapshot. Various tools can be used to directly perform the most elaborate periodic decorations. The concepts of direct and reciprocal lattices have also been interactively implemented based on a previously created 2d-periodic pattern. By extension into the third dimension, the very didactic concept of the Ewald-sphere is used to illustrate the principles of single crystal diffraction with a monochromatic or polychromatic incident beam.

All of the applets which have been developed in this context can be complemented or illustrated further with applications available on other websites.