PSEUDO - a Program for a Pseudosymmetry Search
Online Help - Input Data
Step 4: Select the Supergroup(s)
By now, all of the structure data is given and checked, so the next step is to select
the supergroups you want to check the pseudosymmetry for.
Minimal Supergroups
If you have chosen to search for pseudosymmetry among the minimal supergroups of
the structure's space group, you are provided with a list with all of the minimal
supergroups which contains the group number and HM symbol, as well as the index and the
link to the list with all of the different supergroups of the specified type.
A supergroup is selected if the corresponding checkbox is checked.
To select all of the supergroups, mark the checkbox ``Select all supergroups''.
Specific Supergroup
If you want to search for a pseudosymmetry for a specific supergroup (minimal or
not) you should give this supergroup specifying its number in the ITA, and the
matrix that relates the supergroup conventional basis with the subgroup
conventional basis.
Maximal displacement
At this step, also, the maximal "permitted" displacement
(in Ångströms) of the atoms from their high symmetry positions
should be given. The structure will be considered as pseudosymmetric if the
displacements for all of the atoms necessary to obtain the high symmetry
structure are less or equal to this maximal value.
From the calculations we have made by now(*) we have deduced that the value of
0.75Å is a reasonable one.
(*) We have used this program in the search for pseudosymmetry
among the compounds with symmetry P212121,
Pnma, Pba2 and Pmc21.
J. M. Igartua, M. I. Aroyo, J. M. Pérez-Mato,
Phys. Rev. B54 18 (1996) 12744-12752.
J. M. Igartua, M. I. Aroyo, E. Kroumova, J. M. Pérez-Mato,
Acta Cryst. B55 (1999) 177-185.
(1996) 12744-12752.
Pseudosymmetry search