Materials Laboratory at UPV/EHU

Incommensurate Structures Database

The structures present at this moment have been introduced by hand from the original articles. However the database has to be considered as a collaborative project and therefore are the authors who should correct the actual data and/or introduce new structural information.

This initial database includes mainly structures published in Acta Crystallographica since the search engine at Chester allowed us a rapid collection of the papers.

Some structural parameters have been modified to fulfil the recommendations of the IUCr (for instance thermal displacement parameters in Beta form are not allowed) and to get a unified description of the modulations which permits an easy and safe manipulation of the stored data. In this way the modulations can be only parameterized as:

The structural data is saved in CIF format based on the CIF core dictionary and on the draft of the CIF dictionary for modulated structures, already submitted for approval to COMCIFS.

Apart from the Internet interface, CIF,s are the only way for input and output information from/to the database since CIF,s should be the natural output of crystallographic programs and the unique form of submitting structural data for further publication.

The already stored CIF,s have been checked for consistency and typos. However errors derived from a bad interpretation of the published data or undetected typographic mistakes are still there. Authors are strongly encouraged to revise their data.

The data for an incommensurate structure are divided into 4 sections:

1. General data: chemical information and publication data.

2. Average structure: cell, symmetry, atom sites and experimental data for the average structure if it was separately refined using the main reflections.

3. Modulated structure: cell, symmetry, atom sites and experimental data for the modulated structure.

4. Modulation parameters: description of the modulation, wave vectors, and atom sites modulations.