[IUCr Home Page] [CIF Home Page]

Core CIF Dictionary version 2.3

_reflns_Friedel_coverage

Name

'_reflns_Friedel_coverage'

Category: reflns

Data type: numb

Enumeration range: 0.0 -> 1.0

Definition

    	
   The proportion of Friedel related reflections present in
   the number of the 'independent reflections' specified by
   the item _reflns_number_total.

   This proportion is calculated as the ratio:

     [N(Crystal class) - N(Laue symmetry)] / N(Laue symmetry)

   where, working from the _diffrn_refln_ list,

   N(Crystal class) is the number of reflections obtained on
      averaging under the symmetry of the crystal class
   N(Laue symmetry) is the number of reflections obtained on
      averaging under the Laue symmetry.

   Examples:
     (a) For centrosymmetric structures its value is
         necessarily equal to 0.0 as the crystal class
         is identical to the Laue symmetry.
     (b) For whole-sphere data for a crystal in the space
         group P1, _reflns_Friedel_coverage is equal to 1.0,
         as no reflection h k l is equivalent to -h -k -l
         in the crystal class and all Friedel pairs
         {h k l; -h -k -l} have been measured.
     (c) For whole-sphere data in space group Pmm2, the value
         will be = 0, k >=0, l lead to the
         same value as in (c), whereas measurements of the
         two equivalent octants h >= 0, k, l >= 0 will lead to
         a zero value for _reflns_Friedel_coverage.
 


Copyright © 2003 International Union of Crystallography

IUCr Webmaster