The program PSEUDO looks for a pseudosymmetry in a structure among the (minimal) supergroups of the structure's space group.

The first step in the program is the input of the structure's data. The data can be given using the form or it can be loaded from a CIF file. The necessary data for the structure consists in the number of its space group in the International Tables for Crystallography, Vol A, the lattice parameters (in A and degrees), the number of the atoms in the asymmetric unit and the corresponding atomic positions.

Then, it's necessary to select among what type of supergroups the search is performed. The available options are:

Minimal supergroups

Supergroups for a defined cell multiplication

Supergroup for a well-known transformation matrix

Another option (only for triclinic and monoclinic groups) is to check first the pseudosymmetry of the given cell (obtaining the possible lattice transformations for a given angular tolerance and checking if they are compatible with a space supergroup transformation)

Finally, the program needs a maximum allowed tolerance for pseudosymmetry calculations, i.e., the maximal allowed displacement (in Angstroms) between the mapped atoms of the low symmetry structure obtained by applying the coset representatives of the supergroup with respect to the subgroup (for details, please refer to the article referenced below). Normally a default value of 2Å is a good choice.

When you have filled all of the data, click on the [Show] button to search for pseudosymmetry with respect to the chosen supergroups option.

NOTE: The program only accepts, as input data, structures described in a standard/default setting of the space group. If the original structure is described with respect to an ITA setting, the program SETSTRU can be used to transform it to the standard setting. In the case of more arbitrary non-conventional settings, the tool TRANSTRU can be of some help, if the transformation to the standard setting is known.

If you are using this program in the preparation of a paper, please cite it in the following form:

C. Capillas, E.S. Tasci, G. de la Flor, D. Orobengoa, J.M. Perez-Mato and M.I. Aroyo. "A new computer tool at the Bilbao Crystallographic Server to detect and characterize pseudosymmetry". Z. Krist. (2011), 226(2), 186-196 DOI:10.1524/zkri.2011.1321.

If you are interested in other publications related to Bilbao Crystallographic Server, click
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Formulae

Structure data [in CIF format]

HINT: [ The option for a given filename is preferential ]

Initial Structure (LS)

# Space Group ITA number
99
# Lattice parameters (lengths in angstroems and angles in degrees)
3.999 3.999 4.02 90 90 90
# Number of independent atoms in the asymmetric unit
4
# [atom type] [number] [WP] [x] [y] [z]
Ba 1 - 0.000000 0.000000 0.000000
Ti 2 - 0.500000 0.500000 0.420000
O 3 - 0.500000 0.500000 0.03
O 4 - 0.500000 0.000000 0.58

Select supergroups type for pseudosymmetry search.