Frequently Asked Questions

Chapter 6: Fourier

6.1: How do I calculate a Fourier map to find missing atoms?

You must have already entered the following required information:
 

 
List 1 - Cell
 
List 2 - Symmetry
 
List 3 - Scattering factors
 
List 5 - Parameters (model)
 
List 6 - Observations (reflections)
 
List 14 - Fourier limits
 
List 29 - Asymmetric unit contents

From the Fourier pull-down menu, choose the type of Fourier map that you wish to calculate. You will be presented with a dialog box which allows you to control the subsequent peak search routine.

Use an F-obs map for completing structures with atoms other than hydrogen missing. You will also be given the option to use the Fourier map to refine the positions of existing atoms in the structure.

Use a difference map for completing structures that are almost complete, e.g. to find hydrogen atoms. Using the Add hydrogen option from the Structure menu will place hydrogen geometrically on carbon skeletons and allow you to compare these positions with a difference Fourier map.