Crystals Primer

Chapter 6: Fourier Maps

6.1: Fobs maps

6.2: Special maps

 e.g.
      !\SFLS
      !SCALE
      !END

      !FOURIER
      !END

By default CRYSTALS computes an Fobs Fourier synthesis, with a peak search and without printing the figure field. There are very many options. Phases must be computed before the map, and normally Fobs is put on an absolute scale. The asymmetric part of the unit cell is determined automatically by the SPACEGROUP commands, but may be changed manually in LIST 14.

The peak search leaves the peaks found in the map together with the original atoms in a LIST 10. To convert this to a parameter list, use \PEAKS. If you want to try to assemble the peaks into a molecule, use \COLLECT or \REGROUP after \PEAKS.
 

The MAP directive controls the sort of map to be computed and how it is to be treated. The REFLECTION directive controls the treatment of reflections, and the PEAKS directive controls the peak search.

 e.g.
      !\FOURIER
      !MAP             TYPE=DIFF
      !REFLECTION      WEIGHT=SIM
      !PEAKS           HEIGHT=20
      !END

This requests a Simm weighted difference map, and searches for peaks greater than 2 electrons per cubic angstrom (the scale factor of 10xelectrons is set in LIST 14).