The Bilbao Crystallographic Server

Departamento de Fisica de la Materia Condensada, Universidad del Pais Vasco* Institut fuer Kristallographie, Universitaet Karlsruhe, Germany**
â—‹Mois I. Aroyo* Juan Manuel Perez-Mato* Cesar Capillas* Danel Orobengoa* Hans Wondratschek**

The Bilbao Crystallographic Server (http://www.cryst.ehu.es) is a free web site with crystallographic databases and programs. It has been operating for almost eight years, and new programs are added regularly. The server is built on a core of databases and the different crystallographic applications are classified in shells. The innermost one is formed by simple retrieval tools which are the interface to the set of databases including the data from International Tables, Vols. A, A1 and E. The second shell contains applications which are essential for problems involving group-subgroup relations between space groups. Among them, one can mention programs for determining the different subgroups and supergroups of a given space group type (SUBGROUPGRAPH and SUPERGROUPS) or the splitting of the Wyckoff positions for a group-subgroup pair (WYCKSPLIT). The next shell includes programs on representation theory of space and point groups (REPRES and POINT). Parallel to the crystallographic software the last shell contains more specialized applications of solid-state physics, structural chemistry and crystallography. For example, there exists several tools for the search of pseudosymmetry in crystal structures (PSEUDO, DOPE and BPLOT), for the determination of selection rules - SAM (Infrared and Raman modes) and NEUTRON (phonon extinction rules in inelastic neutron scattering). SYMMODES carries out a group-theoretical analysis of any structural phase transition, calculating the polarization vectors of the possible primary and secondary symmetry modes and the corresponding isotropy subgroups. TRANPATH, a computer program for studies of structural phase transitions with no direct group-subgroup relation between the two end phases is recently made available on the server.