THE BILBAO CRYSTALLOGRAPHIC SERVER: A WEB SITE WITH CRYSTALLOGRAPHIC TOOLS USING THE INTERNATIONAL TABLES

E. Kroumova¹, J.M. Perez-Mato², M.I. Aroyo³, S. Ivantchev², G. Madariaga¹, H. Wondratschek⁴

¹ Departamento Física Aplicada II, Universidad del País Vasco, Apdo. 644, 48080 Bilbao, Spain,
² Departamento de Física de la Materia Condensada, Universidad del País Vasco, Apdo. 644, 48080 Bilbao, Spain,
³ Faculty of Physics, University of Sofia, 1164-Sofia, Bulgaria
⁴ Institut für Kristallographie der Universität Karlsruhe, D-76128 Karlsruhe, Germany.

A Crystallographic WWW Server containing a crystallographic database and a set of related tools is under development at http://lcdx00.wm.lc.ehu.es/cryst/. The database will include the data from the International Tables for Crystallography, vol. A (cf. ITA [1a]) and vol. H (cf. ITH [1b]) stored in a provisional CIF-like format allowing computer transmission. These data serve as a retrieval source for a series of programs designed for solving specific crystallographic problems.

A first version of the server is already available for preliminary testing. At the moment, the database of the server contains part of the data from ITA and ITH. The accompanying software is divided in several shells according to its complexity:

• The first shell contains simple tools for questions that are directly answered by retrieving items of the crystallographic database or by applying simple algorithms:

  • Space-group symbols and numbers
  • Generators and general positions of a space group
  • Wyckoff positions of a space group
  • Maximal subgroups of a space group

• A second shell is formed by more complex programs which in general make use of the tools of the inner shell and calculate specific crystallographic information which is not directly accessible in the database:

• Relations of the Wyckoff positions for a group-subgroup pair (Wyckoff splittings) [2]
• Minimal supergroups of a space group [3]
• Chains of maximal subgroups connecting a group-subgroup pair of specified index
• Graph of maximal subgroups connecting a group-subgroup pair of unspecified index

In addition, the site provides an incipient database of incommensurate structures, which are not being stored in other structural databases because of their peculiar structural parameters. Its first version does not include composite structures, although they have been considered for the design of the database features. The initial interface permits simple queries through the Internet. Input and output of the information is in CIF format based on a provisional CIF dictionary for incommensurate structures, already submitted for approval to COMCIFS.

Further development of the server is planned to include applications of the supergroup-subgroup relations for a specific crystal structures (pseudosymmetry detection [4], mode analysis [5], spectroscopic splitting, aristotype determination, etc...). A second line of expansion is the introduction of additional tools using representation theory and having as main basis a general algorithm for constructing little-group and full-group irreducible representations of space groups.

Crystallographers are kindly invited to use the preliminary version of the Bilbao Crystallographic WWW Server. Any comments or suggestions are highly welcome.

[1a] International Tables for Crystallography, vol. A. Space group Symmetry, Ed. Th.Hahn 4th rev.ed. Kluwer, Dordrecht (1996)

[1b] International Tables for Crystallography, Vol. H, Maximal Subgroups of Plane and Space Groups, Ed. H. Wondratschek (to appear)

[2] Wondratschek, H., Müller, U., Aroyo, M. I., and Sens, I., Z. Kristallogr, 210 (1995), 567

[3] Igartua J. M., Aroyo M.I. and Perez-Mato J.M., Ferroelectrics, 203 (1997), 289

[4] Igartua J. M., Aroyo M.I. and Perez-Mato J.M., Phys. Rev., B 54 (1996), 12744

[5] Aroyo M.I. and Perez-Mato J.M., Acta Cryst., A 54 (1998), 19