Index

Core dictionary version 3.0.14

_reflns.Friedel_coverage

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.
 
   (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 < 1.0 because although reflections h k l and
       -h -k -l are not equivalent when h k l indices are
       non-zero, they are when l=0.
   (d) For a crystal in the 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: Real

Units: none

Category:
reflns