Index

Macromolecular dictionary (mmCIF) version 2.0.09

_reflns.Friedel_coverage

Name:
'_reflns.Friedel_coverage'

Definition:

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

   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, the value of
         _reflns.Friedel_coverage 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,
        _reflns.Friedel_coverage
         will be < 1.0 because although reflections h k l and
         -h -k -l are not equivalent when h k l indices are
         nonzero, they are when l=0.
     (d) For a crystal in space group Pmm2, measurements of the
         two inequivalent octants h >= 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.

Type: float

Mandatory item: no

Alias:
_reflns_Friedel_coverage (cif_core.dic version 2.3)
The permitted range is [0.0, 1.0]

Category: reflns