Index

Core dictionary (coreCIF) version 2.4.5

_reflns_Friedel_coverage

Definition:

   The proportion of Friedel-related reflections present in
   the number of '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, _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 the 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 value of zero for _reflns_Friedel_coverage.

Type: numb

Category: reflns