Bilbao Crystallographic Server SYMMODES Help

SYMMODES - Symmetry Modes

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The software package SYMMODES (Symmetry Modes) provides the necessary tools for a group-theoretical analysis of a structural phase transition characterized by a symmetry change G->H, with G>H. The package combines modules of the programs SUBGROUPGRAPH, WYCKSPLIT and the program SOPD (Subgroup graph Order-Parameter Displacements). The latter has been developed by H.Stokes and D.Hatch (Brigham Young University, Utah, USA) and it is a modified version of the package ISOTROPY.

The results of the symmetry analysis can be summarized as follows:

1. Given the space-group types of G and H, and their index, the program constructs the lattice of maximal subgroups relating G and H. All possible subgroups Hj of the type of H are listed, and their distribution into classes of conjugate subgroups is indicated. In addition, the program also supplies the corresponding transformation matrices relating the (conventional) bases of G to each of the maximal subgroups Hj making up the graph G-H. The particular group-subgroup graph of maximal subgroups for G > Hj, and the corresponding transformation matrices are obtained by specifying the subgroup Hj from the list of all possible subgroups of the type of H.

2. For a given symmetry break G > Hj and a crystal structure specified by the Wyckoff positions of the occupied atomic orbits, the user is supplied with: (i) the number and the patterns of the primary and secondary modes specified by the irreps of G, and the corresponding isotropy subgroups from the G > Hj graph; (ii) the splitting of the Wyckoff positions during the symmetry break G > Hj.

As an input data one should give (or select) the numbers of the group and the subgroup, and the index.

More about the program
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