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9.1 Image Files

An Image file contains all of the information needed to define the position and orientation of all symmetric images of the primary atoms. The file is a card image file and a sample file is given:

       1.0       1.0       1.0
      -1.0       0.0       0.0
       0.0      -1.0       0.0
       0.0       0.0       1.0
       0.0       0.0       0.0

The title is in standard CONGEN format, see Syntactic Glossary. The next contains the number of transformations (I5). The following line contains the unit cell dimensions (multiplying factors) (3F10.5).

The remaining lines are in groups of five, one group for each transformation . For each group, the first line contains the name of the transformation (A8). The next three lines contains the rotation matrix, and the last line contains the translation vector (all 3F10.5).

The rotation matrix must be unitary, however, a non-unitary rotation matrix will only result in a warning. The use of an anti-unitary matrix can be used to include the mirror image of any system into the calculation. The values of the translation vector are multiplied by the cell dimensions listed at the beginning of the file to generate the actual translation steps. For the use in this program the translation is done after the rotation has been made.

One other restriction on the transformations is that every transformation must have an inverse. Again, there is only a warning if this restriction is violated as there may be examples where this is desired. In the example above, this transformation is its own inverse. Non-physical results will be obtained if this restriction is violated.

The maximum number of allowed transformations is 26 (the number needed for simple 3-dimensional periodic boundaries). This limit can easily be increased by modifying INIMAG.

For other examples of image files see the test cases.