A DEMONSTRATION OF THE FULL ICSD-FOR-WWW INORGANIC STRUCTURE DATABASE
Institut Max von Laue - Paul Langevin, B.P. 156X, Grenoble Cedex 9, 38042 FRANCE (hewat@ill.fr)
The Inorganic Crystal Structure Database (ICSD) contains more than 45,000 references including atomic co-ordinates to "all" inorganic structures. It is an essential tool for inorganic crystallographers, and of interest to many other scientists and teachers. We will demonstrate the intranet version ICSD-for-WWW, which contains powerful search criteria, bond length and angle calculations, powder diffraction simulation, and interactive 3D drawings of the structures.
But why use ICSD-for-WWW when ICSD is available cheaply on a PC CD-rom ? Crystallographers are vitally interested in making the results of their work available to the many other scientists working in solid state physics and chemistry, and of course to those teaching these subjects. There is a need to quickly search for references and then present crystal structure drawings in an automatic manner that can be understood by everyone. An obvious solution would be to make the database available on the WWW, so that it might be accessed from every kind of computer, not just one particular PC.
Recent advances in WWW technology mean that an interactive Graphic User Interface (GUI) can be constructed similar to those available on the Macintosh and Windows-95 systems, and the Virtual Reality Modelling Language (VRML) can be used to draw high quality interactive 3D drawings of the crystal structure. Indexed powder diffraction patterns can also be created, displayed and printed in high resolution postscript. Because of the intense competition between Microsoft, Netscape and others, the performance of VRML viewers is rapidly outstripping that of proprietary 3D applications on PC's. And if a PC is insufficient, the same VRML file can be displayed on a Silicon Graphics workstation. Our local WWW server is easily as fast running ICSD-for-WWW as a Pentium-PC running the MS-DOS version.
How does it work in practice ? The ICSD for WWW interface consists of a number of small boxes, labelled 'Authors', 'Elements', 'Minerals' etc. The user enters something in at least one box and presses the 'Go' button to find how many structures qualify. He may enter more criteria to refine the search to a hundred or so entries before listing them. There are buttons to arrange the entries according to the year, formula, space group or mineral name. The user selects one of the listed entries to display the complete entry, the bond lengths and angles, the powder pattern and the structure.
For example, to find authors whose names start with "le" it is sufficient to enter "le" in the 'Authors' box and click 'Go'. To find copper oxides containing 3-5 different elements, where copper exhibits a formal oxidation state of between +2.2 and +2.5, enter "O Cu+2.2 to Cu+2.5" in the 'Elements' box and "3-5" in the 'Element Count' box. The syntax is not very strict; for example "1990-1995", "90 to 95" etc are all recognised as a range of years. Help on any particular box is obtained by clicking the title of the box, but the interface can be used without instruction because it is quite intuitive, similar to other WWW interfaces, and appears the same on all computers.
The structure drawing and powder pattern interfaces can be used automatically to produce a standard display. If atomic bonding is not specified, the programme tries to guess, which is often sufficient for a non-crystallographer. For example the famous 123-superconductor drawing, complete with co-ordination polyhedrae and copper oxide chains, is displayed automatically without any special user input. Of course the atom co-ordinates, unit cell and symmetry are also displayed and can be edited, for example to see the effect of modifying the structure. Of course the best way of learning about ICSD for WWW is to try it !