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cif_twinning.dic CIF dictionary

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Category view of data-item definitions

_TWIN_[]
CIF 
Data items in the TWIN category record general details about

the nature of the twinning in the sample.
Terminology for twin dataname definitions was taken directly from:
"International Union of Crystallography Commission on Mathematical
and Theoretical Crystallography Research themes: Crystal twinning"
by Massimo Nespolo, February 3, 2009.
http://www.crystallography.fr/mathcryst/twins.htm .

Example:
_twin_formation_mechanism         gt
    _twin_dimensionality              triperiodic
    _twin_morphology                  polysynthetic
    _twin_special_details
    ;        This is an example of a twin in space group P 32
             by the 2 x,x,0 twin operation.
    ;

    loop_
       _twin_individual_id
       _twin_individual_mass_fraction_refined
       _twin_individual_twin_lattice_type
       _twin_individual_twin_matrix_11
       _twin_individual_twin_matrix_12
       _twin_individual_twin_matrix_13
       _twin_individual_twin_matrix_21
       _twin_individual_twin_matrix_22
       _twin_individual_twin_matrix_23
       _twin_individual_twin_matrix_31
       _twin_individual_twin_matrix_32
       _twin_individual_twin_matrix_33
          1 0.545(2) ref   1  0  0  0  1  0  0  0  1
          2 0.455(2) mt_II 0  1  0  1  0  0  0  0 -1

    loop_
       _twin_refln_datum_id
       _twin_refln_individual_id
       _twin_refln_index_h
       _twin_refln_index_k
       _twin_refln_index_l
       _twin_refln_F_squared_calc
       _twin_refln_F_squared_meas
       _twin_refln_F_squared_sigma
       _twin_refln_include_status
          1    1  -1   1 -32     40.17     55.86      7.39 o
          1    2   1  -1  32     40.17     55.86      7.39 o
          2    1   0   1 -32    125.83    145.63      9.36 o
          2    2   1   0  32    125.83    145.63      9.36 o
          3    1   1   1 -32     10.33     30.89      7.39 o
          3    2   1   1  32     10.33     30.89      7.39 o
          4    1  -3   2 -32     28.26     26.84      9.47 o
          4    2   2  -3  32     28.26     26.84      9.47 o
          5    1  -2   2 -32      4.31     13.21      9.78 o
          5    2   2  -2  32      4.31     13.21      9.78 o
          6    1  -1   2 -32     10.71     17.48      9.88 o
          6    2   2  -1  32     10.71     17.48      9.88 o
          7    1   0   2 -32     13.94     37.66     10.51 o
          7    2   2   0  32     13.94     37.66     10.51 o
          8    1   1   2 -32     58.60     75.41      9.88 o
          8    2   2   1  32     58.60     75.41      9.88 o
          9    1  -2   3 -32     27.75     41.40      8.01 o
          9    2   3  -2  32     27.75     41.40      8.01 o
         10    1  -1   3 -32     59.22     65.53      8.11 o
         10    2   3  -1  32     59.22     65.53      8.11 o

data_twin_[]
    _name                 '_twin_[]'
    _category             category_overview
    _type                 null
    _definition

;    Data items in the TWIN category record general details about
     the nature of the twinning in the sample.
     Terminology for twin dataname definitions was taken directly from:
     "International Union of Crystallography Commission on Mathematical 
     and Theoretical Crystallography Research themes: Crystal twinning"
     by Massimo Nespolo, February 3, 2009.
     http://www.crystallography.fr/mathcryst/twins.htm . 
;

    _example
# -----------------------------------------------------------------------------

;
    _twin_formation_mechanism         gt
    _twin_dimensionality              triperiodic
    _twin_morphology                  polysynthetic
    _twin_special_details
    ;        This is an example of a twin in space group P 32
             by the 2 x,x,0 twin operation.
    ;

    loop_
       _twin_individual_id
       _twin_individual_mass_fraction_refined
       _twin_individual_twin_lattice_type
       _twin_individual_twin_matrix_11 
       _twin_individual_twin_matrix_12
       _twin_individual_twin_matrix_13
       _twin_individual_twin_matrix_21
       _twin_individual_twin_matrix_22
       _twin_individual_twin_matrix_23
       _twin_individual_twin_matrix_31
       _twin_individual_twin_matrix_32
       _twin_individual_twin_matrix_33
          1 0.545(2) ref   1  0  0  0  1  0  0  0  1
          2 0.455(2) mt_II 0  1  0  1  0  0  0  0 -1

    loop_ 
       _twin_refln_datum_id
       _twin_refln_individual_id
       _twin_refln_index_h 
       _twin_refln_index_k 
       _twin_refln_index_l 
       _twin_refln_F_squared_calc 
       _twin_refln_F_squared_meas 
       _twin_refln_F_squared_sigma 
       _twin_refln_include_status 
          1    1  -1   1 -32     40.17     55.86      7.39 o        
          1    2   1  -1  32     40.17     55.86      7.39 o        
          2    1   0   1 -32    125.83    145.63      9.36 o        
          2    2   1   0  32    125.83    145.63      9.36 o        
          3    1   1   1 -32     10.33     30.89      7.39 o        
          3    2   1   1  32     10.33     30.89      7.39 o        
          4    1  -3   2 -32     28.26     26.84      9.47 o        
          4    2   2  -3  32     28.26     26.84      9.47 o        
          5    1  -2   2 -32      4.31     13.21      9.78 o        
          5    2   2  -2  32      4.31     13.21      9.78 o       
          6    1  -1   2 -32     10.71     17.48      9.88 o        
          6    2   2  -1  32     10.71     17.48      9.88 o     
          7    1   0   2 -32     13.94     37.66     10.51 o         
          7    2   2   0  32     13.94     37.66     10.51 o    
          8    1   1   2 -32     58.60     75.41      9.88 o        
          8    2   2   1  32     58.60     75.41      9.88 o   
          9    1  -2   3 -32     27.75     41.40      8.01 o        
          9    2   3  -2  32     27.75     41.40      8.01 o  
         10    1  -1   3 -32     59.22     65.53      8.11 o       
         10    2   3  -1  32     59.22     65.53      8.11 o 

;
# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    _example_detail
;
 The twinning example presented here shows twinning by merohedry for
 a trigonal crystal system. The simulated space group is P 32 2 1, but
 the true space group is P 32. The twin operation chosen is 2: x, x, 0 in
 P 32 2 1 corresponding to operation (by rows) 0, 1, 0 / 1, 0, 0 / 0, 0, -1
 [see Table 11.2.2.1 of International Tables for Crystallography
 (2005), Vol. A].

 The TWIN_REFLN loop gives the properties of each diffraction peak
 (identified by _twin_refln_datum_id) which is indexed 
 to both the twin individuals.
 
 In each of the loops shown in this example the first items on a line 
 are the list reference.  While the list reference must be present 
 in every loop, it is not necessary that it should be declared as the
first item in the loop.
;
_twin_dimensionality
CIF 
The degree of overlap between the twin lattices.
Most twin lattice symmetry (TLS) and twin lattice quasi-symmetry (TLQS)
twins as defined by Donnay and Donnay will be triperiodic.

Reference: Donnay, G. & Donnay, J. D. H. (1974). Can. Mineral. 12, 422-425.

data_twin_dimensionality
    _name                  '_twin_dimensionality'
    _category              twin
    _type                  char
    _list                  no
    loop_ _enumeration
    	  _enumeration_detail
              triperiodic   'common lattice in three dimensions'
              diperiodic    'common lattice in two dimensions'
              monoperiodic  'common lattice in one dimension'
    _definition
;
   The degree of overlap between the twin lattices.  
   Most twin lattice symmetry (TLS) and twin lattice quasi-symmetry (TLQS) 
   twins as defined by Donnay and Donnay will be triperiodic.  

   Reference: Donnay, G. & Donnay, J. D. H. (1974). Can. Mineral. 12, 422-425. 
;
_twin_formation_mechanism
CIF 
A description of the method of twin formation.

data_twin_formation_mechanism
    _name         '_twin_formation_mechanism'
    _category     twin
    _type         char
    _list         no
    loop_ 
       _enumeration
    	  _enumeration_detail
        gt    'growth twin formed during crystal growth'
        tt    'transformation twin formed during phase transition'
        mt    'mechanical twin formed as a result of mechanical action'
    _definition
;
     A description of the method of twin formation.
;
_twin_morphology
CIF 
The physical relationship of the different twins to one another.

data_twin_morphology
    _name       '_twin_morphology'
    _category   twin
    _type       char
    _list       no
    loop_ 
       _enumeration
       _enumeration_detail
        contact        'separated by a surface'
        penetration    'sharing a volume'
        simple         'individuals are not repeated'
        polysynthetic  'individuals repeat in approximately linear arrangement'
        cyclic         'individuals repeat in closed edifice'

    _definition
;
 The physical relationship of the different twins to one another.
;
_twin_special_details
CIF 
Information about twinning in the sample not contained in other data items.

Example:
Individuals 3 and 4 arise from form (I) following an
    enantiotropic phase transition by sudden cooling in
    a cryostat to 173K.

data_twin_special_details
    _name            '_twin_special_details'
    _category         twin
    _type             char
    _list             no
    _example
;   Individuals 3 and 4 arise from form (I) following an
    enantiotropic phase transition by sudden cooling in
    a cryostat to 173K. 
;
    _definition
;
    Information about twinning in the sample not contained in other data items.
;


##########################
## TWIN_INDIVIDUAL      ##
##########################
_twin_individual_twin_lattice_type
CIF 
Identification of the symmetry relationships between the
twin lattices as described in International Tables
for Crystallography (2004), Vol. C, Chapter 1.3.
The twin with the identity matrix should be denoted as 'ref'.

data_twin_individual_twin_lattice_type
    _name                     '_twin_individual_twin_lattice_type'
    _category                 twin
    _type                     char
    _list                     yes 
    loop_ _enumeration
    	  _enumeration_detail
               ref        'reference twin'
               mt_I       'merohedral class I (simple inversion)'
               mt_II      'merohedral class II (mirror or twofold)'
               mt_I+II    'class I and II simultaneously present'
               rmt        'reticular merohedral'
               pmt        'pseudo-merohedral'
               rpmt       'reticular pseudo-merohedral'
               nmt        'non-merohedral'
    _definition
;
       Identification of the symmetry relationships between the 
       twin lattices as described in International Tables 
       for Crystallography (2004), Vol. C, Chapter 1.3.  
       The twin with the identity matrix should be denoted as 'ref'.
;
_TWIN_INDIVIDUAL_[]
CIF 
Data items in the TWIN_INDIVIDUAL category describe properties

of each twinned individual, and the symmetry relationships
between the individuals.

data_twin_individual_[]
    _name            '_twin_individual_[]'
    _category        category_overview
    _type            null
    _definition
;        Data items in the TWIN_INDIVIDUAL category describe properties 
         of each twinned individual, and the symmetry relationships 
         between the individuals.
;
_twin_individual_id
CIF 
The unique identifier for this twin individual.
The twin for which _twin_individual_twin_matrix_
is the identity matrix is called the reference twin.
It is recommended that the reference twin be labelled '1'.

data_twin_individual_id
     _name                '_twin_individual_id'
     _category            twin_individual
     _type                char
     _list                yes
     _list_mandatory      yes
     _list_link_child	  
              '_twin_refln_individual_id'
     _definition
;
      The unique identifier for this twin individual. 
      The twin for which _twin_individual_twin_matrix_
      is the identity matrix is called the reference twin.  
      It is recommended that the reference twin be labelled '1'. 
;
_twin_individual_mass_fraction_refined
CIF 
The refined mass fraction of this twin individual; the sum
of all mass fractions must equal unity within the limits of
experimental uncertainty.

data_twin_individual_mass_fraction_refined
     _name             '_twin_individual_mass_fraction_refined'
     _category		  twin_individual
     _type             numb
     _type_conditions	  esd
     _list             yes
     _list_reference	  '_twin_individual_id'
     _enumeration_range 0:1.0
     _definition
;
      The refined mass fraction of this twin individual; the sum
      of all mass fractions must equal unity within the limits of 
      experimental uncertainty.
;
_twin_individual_twin_matrix
CIF 
Data names:
_twin_individual_twin_matrix_11
_twin_individual_twin_matrix_12
_twin_individual_twin_matrix_13
_twin_individual_twin_matrix_21
_twin_individual_twin_matrix_22
_twin_individual_twin_matrix_23
_twin_individual_twin_matrix_31
_twin_individual_twin_matrix_32
_twin_individual_twin_matrix_33

Elements of the matrix U that multiplies the Miller indices h,k,l
of the reference twin to give the Miller indices h',k',l',
of the twin specified by _twin_individual_id

(h' k' l') = U (h k l )

It follows that the reference twin must have U = I, the identity matrix.

data_twin_individual_twin_matrix_
     loop_ _name          '_twin_individual_twin_matrix_11'
                          '_twin_individual_twin_matrix_12'
                          '_twin_individual_twin_matrix_13'
                          '_twin_individual_twin_matrix_21'
                          '_twin_individual_twin_matrix_22'
                          '_twin_individual_twin_matrix_23'
                          '_twin_individual_twin_matrix_31'
                          '_twin_individual_twin_matrix_32'
                          '_twin_individual_twin_matrix_33'
     _category            'twin_individual'
     _type		          numb
     _list		          yes
     _list_reference	     '_twin_individual_id'
     _definition
;
     Elements of the matrix U that multiplies the Miller indices h,k,l 
     of the reference twin to give the Miller indices h',k',l', 
     of the twin specified by _twin_individual_id 

                         (h' k' l') = U (h k l )

     It follows that the reference twin must have U = I, the identity matrix. 
;     


################
## twin_refln ##
################
_TWIN_REFLN_[]
CIF 
Items in the TWIN_REFLN category tabulate the calculated values of F^2^
for each peak observed in the diffraction pattern,
together with the measured value of F^2^.
The calculated F^2^ for an observed peak is a weighted sum
of the contribution of all the twin components.
The calculated structure factor for each twin contribution can also
be given.

Examples:
loop_
     _twin_refln_datum_id
     _twin_refln_individual_id
     _twin_refln_index_h
     _twin_refln_index_k
     _twin_refln_index_l
     _twin_refln_F_squared_meas
     _twin_refln_F_squared_sigma
     _twin_refln_include_status

   1  1   1   0   0             1.03      0.18 o
   1  3   1   0   0             1.03      0.18 o
   2  1   2   0   0          1290.01     55.59 o
   2  3   2   0   0          1290.01     55.59 o
   3  1   3   0   0             2.59      0.42 o
   3  3   3   0   0             2.59      0.42 o
   4  1   4   0   0            30.98      1.47 o
   4  3   4   0   0            30.98      1.47 o
   5  1   5   0   0             1.97      0.96 o
   5  3   5   0   0             1.97      0.96 o
   6  1   6   0   0             1.55      1.14 o
   6  2   6   1   2             1.55      1.14 o
   6  3   6   0   0             1.55      1.14 o
   6  4   6   1   2             1.55      1.14 o
   7  1  -6   1   0             0.47      1.06 o
   7  2   6   2   2             0.47      1.06 o

loop_
     _twin_refln_datum_id
     _twin_refln_individual_id
     _twin_refln_index_h
     _twin_refln_index_k
     _twin_refln_index_l
     _twin_refln_F_squared_calc
     _twin_refln_F_squared_meas
     _twin_refln_F_squared_sigma
     _twin_refln_include_status

   620   1   1  -6  -3      200.22      207.88      3.35 o
   621   1  -1   6   3      225.34      224.15      3.62 o
   622   2  -1   6   3      184.64      196.34      3.95 o
   623   1  -1  -6  -3      173.28      181.13      3.06 o
   624   2  -1  -6  -3      143.40      152.05      2.78 o
   625   1   1   6   3      204.45      204.38      4.48 o
   625   2   3  -6   1      204.45      204.38      4.48 o
   626   1   3  -6  -3      240.97      241.19      3.75 o
   626   2  -3   6   3      240.97      241.19      3.75 o
   627   1   3   6   3      288.54      281.53      4.31 o
   627   2  -3  -6  -3      288.54      281.53      4.31 o
   628   1  -5  -6  -3      179.56      176.35      5.36 o
   628   2  -3   6   5      179.56      176.35      5.36 o
   629   1   5   6   3      235.04      238.84      4.06 o
   629   2  -5  -6  -3      235.04      238.84      4.06 o

data_twin_refln_[]
    _name                      '_twin_refln_[]'
    _category                    category_overview
    _type                        null
    _definition
;
    Items in the TWIN_REFLN category tabulate the calculated values of F^2^ 
    for each peak observed in the diffraction pattern, 
    together with the measured value of F^2^.
    The calculated F^2^ for an observed peak is a weighted sum 
    of the contribution of all the twin components.
    The calculated structure factor for each twin contribution can also
    be given.
; 
    loop_ _example
          _example_detail
# - Example 1  - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
;  
  loop_
     _twin_refln_datum_id
     _twin_refln_individual_id
     _twin_refln_index_h 
     _twin_refln_index_k 
     _twin_refln_index_l 
     _twin_refln_F_squared_meas 
     _twin_refln_F_squared_sigma 
     _twin_refln_include_status 

   1  1   1   0   0             1.03      0.18 o  
   1  3   1   0   0             1.03      0.18 o         
   2  1   2   0   0          1290.01     55.59 o  
   2  3   2   0   0          1290.01     55.59 o  
   3  1   3   0   0             2.59      0.42 o  
   3  3   3   0   0             2.59      0.42 o  
   4  1   4   0   0            30.98      1.47 o  
   4  3   4   0   0            30.98      1.47 o  
   5  1   5   0   0             1.97      0.96 o  
   5  3   5   0   0             1.97      0.96 o  
   6  1   6   0   0             1.55      1.14 o  
   6  2   6   1   2             1.55      1.14 o  
   6  3   6   0   0             1.55      1.14 o  
   6  4   6   1   2             1.55      1.14 o  
   7  1  -6   1   0             0.47      1.06 o  
   7  2   6   2   2             0.47      1.06 o  
;
#---------------------------------------------------------------------

# Description of Example 1
;
   This partial listing describes seven observed diffraction peaks 
   in a four-individual twin by non-merohedry. The reference individual
   is 1. Reflections from the other three individuals 2, 3 and 4 are 
   present only if these cannot be experimentally separated from the 
   reference individual. 
;    

# ---- Example 2 ------------------------------------------------------
;
  loop_
     _twin_refln_datum_id
     _twin_refln_individual_id
     _twin_refln_index_h       
     _twin_refln_index_k 
     _twin_refln_index_l 
     _twin_refln_F_squared_calc 
     _twin_refln_F_squared_meas 
     _twin_refln_F_squared_sigma 
     _twin_refln_include_status 

   620   1   1  -6  -3      200.22      207.88      3.35 o  
   621   1  -1   6   3      225.34      224.15      3.62 o   
   622   2  -1   6   3      184.64      196.34      3.95 o    
   623   1  -1  -6  -3      173.28      181.13      3.06 o   
   624   2  -1  -6  -3      143.40      152.05      2.78 o   
   625   1   1   6   3      204.45      204.38      4.48 o   
   625   2   3  -6   1      204.45      204.38      4.48 o   
   626   1   3  -6  -3      240.97      241.19      3.75 o   
   626   2  -3   6   3      240.97      241.19      3.75 o  
   627   1   3   6   3      288.54      281.53      4.31 o   
   627   2  -3  -6  -3      288.54      281.53      4.31 o  
   628   1  -5  -6  -3      179.56      176.35      5.36 o   
   628   2  -3   6   5      179.56      176.35      5.36 o  
   629   1   5   6   3      235.04      238.84      4.06 o   
   629   2  -5  -6  -3      235.04      238.84      4.06 o  
;
# --------------------------------------------------------------------
;
 This example is taken from Colombo Young & Gladfelter
 [Inorg. Chem. (2000), 39, 4621-4624]. 
 Two structures of nitronium tetranitratogallate
 are reported as a result of an enantiotropic phase transition. 
 The higher-temperature phase is in the tetragonal space group I-4, 
 while the lower-temperature phase is a twin by non-merohedry 
 in space group I2. 
 The individuals are enantiomorphic as a result of the phase transition. 
 In the listing it is clear that datums 620-624 do not contain 
 overlapping reflections, whereas datums 625-629 contain contributions 
 from both twins.
;
_twin_refln_datum_id
CIF 
This item serves to identify an observed diffraction peak.
It may include contributions from one or more twin components
and so may appear more than once in the list.
The values of _twin_refln_F_squared_calc and
_twin_refln_F_squared_meas indexed by
_twin_refln_datum_id include the contributions from all the twins.
The diffraction peak is indexed by
_twin_refln_index_h, *_k and *_l referred to the cell of
the twin component identified by _twin_refln_individual_id.

The list reference includes both _twin_refln_datum_id and
_twin_refln_individual_id.  The combination of these two items
may only appear once in a list.

data_twin_refln_datum_id
     _name            '_twin_refln_datum_id'
     _category         twin_refln
     _type             char
     _list             yes
     _list_mandatory   yes
     _definition
;
     This item serves to identify an observed diffraction peak. 
     It may include contributions from one or more twin components
     and so may appear more than once in the list.  
     The values of _twin_refln_F_squared_calc and 
     _twin_refln_F_squared_meas indexed by
     _twin_refln_datum_id include the contributions from all the twins.  
     The diffraction peak is indexed by 
     _twin_refln_index_h, *_k and *_l referred to the cell of 
     the twin component identified by _twin_refln_individual_id.  
     
     The list reference includes both _twin_refln_datum_id and 
     _twin_refln_individual_id.  The combination of these two items 
     may only appear once in a list. 
;
_twin_refln_F_squared_calc
CIF 
Calculated value for the overall squared structure factors (in
electrons squared for X-ray diffraction) arising from all
the twin contributions to the peak defined by _twin_refln_datum_id.
The total contribution from all twins to a single observed
reflection is modelled according to the method of Pratt, Coyle
and Ibers as follows:

_twin_refln_F_squared_calc = osf * Sum (mf * _refln_F_squared_calc)

where osf is the overall scale factor,
mf is the mass fraction,
and the sum is taken over all the twin components that contribute
to this diffraction peak.

Reference: Pratt, C. S., Coyle, B. A. & Ibers, J. A. (1971).
J. Chem. Soc. A, pp. 2146-2151.

data_twin_refln_F_squared_calc
    _name                        '_twin_refln_F_squared_calc'
    _category                    twin_refln
    _type                        numb
    _list                        yes
loop_
    _list_reference        '_twin_refln_datum_id' '_twin_refln_individual_id'
    _definition 
; 

        Calculated value for the overall squared structure factors (in
        electrons squared for X-ray diffraction) arising from all 
        the twin contributions to the peak defined by _twin_refln_datum_id.  
        The total contribution from all twins to a single observed
        reflection is modelled according to the method of Pratt, Coyle
        and Ibers as follows:

        _twin_refln_F_squared_calc = osf * Sum (mf * _refln_F_squared_calc)

        where osf is the overall scale factor,
        mf is the mass fraction,
        and the sum is taken over all the twin components that contribute
        to this diffraction peak.

        Reference: Pratt, C. S., Coyle, B. A. & Ibers, J. A. (1971).
        J. Chem. Soc. A, pp. 2146-2151.
;
_twin_refln_F_squared_calc_individual
CIF 
Contribution of the twin identified by _twin_refln_individual_id
to _twin_refln_F_squared_calc.

_twin_refln_F_squared_calc_individual = osf * mf * _refln_F_squared_calc

where osf is the overall scale factor, mf is the mass factor.
For X-ray diffraction the units are electrons squared.



data_twin_refln_F_squared_calc_individual
    _name                        '_twin_refln_F_squared_calc_individual'
    _category                    twin_refln
    _type                        numb
    _list                        yes
loop_
    _list_reference        '_twin_refln_datum_id' '_twin_refln_individual_id'
    _definition 
; 

        Contribution of the twin identified by _twin_refln_individual_id 
        to _twin_refln_F_squared_calc. 

        _twin_refln_F_squared_calc_individual = osf * mf * _refln_F_squared_calc

        where osf is the overall scale factor, mf is the mass factor.
        For X-ray diffraction the units are electrons squared.

;









_twin_refln_F_squared_meas


CIF 

The observed value F^2^ of the peak referenced by
_twin_refln_datum_id. This is typically the observed peak
intensity after Lorentz and polarization corrections.



data_twin_refln_F_squared_meas
    _name                        '_twin_refln_F_squared_meas'
    _category                    twin_refln
    _type                        numb
    _list                        yes
loop_
    _list_reference        '_twin_refln_datum_id' '_twin_refln_individual_id'

    _definition 
;
         The observed value F^2^ of the peak referenced by 
         _twin_refln_datum_id. This is typically the observed peak
         intensity after Lorentz and polarization corrections.
;









_twin_refln_F_squared_sigma


CIF 

Standard uncertainty of _twin_refln_F_squared_meas



data_twin_refln_F_squared_sigma
    _name                        '_twin_refln_F_squared_sigma'
    _category                    twin_refln
    _type                        numb
    _list                        yes
loop_
    _list_reference        '_twin_refln_datum_id' '_twin_refln_individual_id'

    _definition 
;
            Standard uncertainty of _twin_refln_F_squared_meas
;









_twin_refln_include_status


CIF 

A symbol indicating how the reflection is treated during refinement.



data_twin_refln_include_status
     _name               '_twin_refln_include_status'
     _category           twin_refln
     _type               char
     _list               yes
loop_
    _list_reference        '_twin_refln_datum_id' '_twin_refln_individual_id'
    loop_ _enumeration
          _enumeration_detail    
     o
;            (lower-case letter o for 'observed')
             satisfies _refine_ls_d_res_high
             satisfies _refine_ls_d_res_low
             exceeds _reflns_threshold_expression
;
     <;
;            satisfies _refine_ls_d_res_high
             satisfies _refine_ls_d_res_low
             does not exceed _reflns_threshold_expression
;
     -       'systematically absent reflection'
     x       'unreliable measurement -- not used'
     r       'removed from the refinement for other reasons'
     h       'does not satisfy _refine_ls_d_res_high'
     l       'does not satisfy _refine_ls_d_res_low'
          _enumeration_default         o

     _definition
;
    A symbol indicating how the reflection is treated during refinement.
;









_twin_refln_index


CIF 

Data names:
_twin_refln_index_h
_twin_refln_index_k
_twin_refln_index_l

Miller indices of a reflection from the twin component
labelled by _twin_refln_individual_id.
The values of the Miller indices must correspond
to the cell defined for this twin component.



data_twin_refln_index_
    loop_ _name              '_twin_refln_index_h'
                             '_twin_refln_index_k'
                             '_twin_refln_index_l'
    _category                 twin_refln
    _type                     numb
    _list                     yes
loop_
    _list_reference        '_twin_refln_datum_id' '_twin_refln_individual_id'
    _definition
;
     Miller indices of a reflection from the twin component 
     labelled by _twin_refln_individual_id. 
     The values of the Miller indices must correspond 
     to the cell defined for this twin component.  
;









_twin_refln_individual_id


CIF 

The unique identifier of the twin individual
whose Miller indices are given in _twin_refln_index_.
The ID must match a _twin_individual_id in the
TWIN_INDIVIDUAL category.

The list reference includes both _twin_refln_datum_id and
_twin_refln_individual_id.  The combination of these two items
may only appear once in a list.



data_twin_refln_individual_id
     _name               '_twin_refln_individual_id'
     _category           twin_refln
     _type               char
     _list               yes
     _list_mandatory     yes
     _list_link_parent   '_twin_individual_id' 
loop_
    _list_reference        '_twin_refln_datum_id' '_twin_refln_individual_id'
     _definition
;
      The unique identifier of the twin individual 
      whose Miller indices are given in _twin_refln_index_.  
      The ID must match a _twin_individual_id in the 
      TWIN_INDIVIDUAL category.  

     The list reference includes both _twin_refln_datum_id and 
     _twin_refln_individual_id.  The combination of these two items 
     may only appear once in a list. 
;












Revision history






2012-07-25 Created from Victor Young's draft text. JRH



2012-08-20 Added category definitions and corrected _list for
_twin_lattice_type. JRH



2012-08-21 cosmetic changes such as arranging the items
alphabetically and added queries for VY. I.D.Brown



2012-08-28 Inserted changes from V. Young as per I.D. Brown's
comments; removed _example_detail for twin category; corrected
_list_reference for _refln_ category; added explanation for
_refln_F_squared_ . JRH



2012-08-31 Added _twin_special_details with example from VY. JRH



2013-01-17 Corrected equation defining F_calc. JRH



2013-01-18 Moved _refln_ items into separate _twin_refln category and
rewrote definitions for clarity.



2013-03-13 Added missing _twin_refln_index_ . JRH



2013-03-25 IDB: Added enumeration range to
_twin_individual__mass_fraction_refined and rewrote
the definition
Rewrote the definition of _twin_individual_twin_matrix
Raised queries about what the _twin_refln category
is actually recording.



2013-05-09 JRH: corrected _twin_refln_F_calc equation; added
_list_reference to _twin_refln_h, *_k, *_l definition;
fiddled with _twin_individual_twin_id definition text



2013-06-26 JRH,VY: added further example to TWIN category



2013-06-26 some syntax and formatting errors corrected (BM)



2013-06-27 IDB Changed  _twin_refln_observed_status to
_twin_refln_include_status
Added the twin_contibution category
Reworked the twin_refln category to change the list reference
to _twin_refln_datum_id (name changed from _*_datum_index
Made some improvements to the definitions.
Converted space group symbols to CIF conventions
Arranged items in alphabetic order to conform
to other dictonaries.



2013-07-11 JRH edited examples to reflect proposed changes from IDB



2013-07-29 VGY modified examples to comply with IDB's suggested changes
(see below). These are within comments, but not yet integrated
into the text of the document. Added nmt for non-merohedral
twin into data_twin_lattice_type. Somehow this was removed.



2013-08-16 VGY made corrections as directed by JH in examples 2 and 3.
Removed work for these examples from commented text and
integrated into document. Updated example 1 to include explicit
_twin_contribution items for individual 2.



2013-09-02 JRH edited in latest examples from VGY after email discussion



2013-09-03 JRH: move lattice_twin_type into twin_individual category; add
'ref' lattice twin type. Changed _twin_contribution_twin_id to
_twin_contribution_individual_id



2013-09-03 VGY: improve example to include single-contributor reflections
coming from different individuals.



2013-09-13 IDB: Changed _refln_twin to _twin_refln,
improved wording of some definitions, corrected syntax errors,
added _twin_refln_include_status,
removed '_mandatory yes' from _twin_refln_index_
Rearranged the order of items in some examples to put the
list reference first.



2013-11-13 IDB: Following comments from Tony Linden and George Sheldrick
an alternative version of twin_refln is proposed.
If this is adopted _twin_contribution would be dropped.



2013-12-04 IDB: The alternative twin_refln is adopted and
twin_contribution is deleted.



2012-12-04 Minor spelling corrections,removal of old twin_contribution
material and example clarification added. VGY



2012-12-05 IDB: Made changes in the description of the example
under the twin category to reflect the deletion
of the twin_contribution category.
Removed '_twin_contribution_individual_id' from
_link_list_child in the definition of _twin_individual_id.
Modified the description of the twin_refln category
to reflect the merging of twin_contribution with twin_refln.
Added r to enumeration list of _twin_refln_include_status.



2014-02-14  BMcM and NJA: minor editing for clean release version










 


 











     

     



  
  

  							
    
  
    
 
      
      

  
						
  




International Tables for Crystallography


Volume G: Definition and exchange of crystallographic data


First online edition (2006)


Edited by S. R. Hall and B. McMahon



An essential guide and reference to CIF for programmers, data managers handling crystal-structure information and practising crystallographers.