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New version of CIF Core dictionary (2.4)

  • To: comcifs@iucr.org
  • Subject: New version of CIF Core dictionary (2.4)
  • From: Brian McMahon <bm@iucr.org>
  • Date: Tue, 18 Dec 2007 10:06:13 +0000
  • Reply-To: "Discussion list of the IUCr Committee for the Maintenance of the CIF Standard (COMCIFS)" <comcifs@iucr.org>
Dear COMCIFS

The Core Dictionary Management Group proposes a number of additions
to the core dictionary and a few minor revisions to existing content,
and requests the voting members of COMCIFS to approve these changes.
The changes are summarised below (the additional data items are
listed explicitly). The discussions of the coreDMG are available
at http://www.iucr.org/iucr-top/lists/coredmg/index.html

This draft has been approved following technical review by the
Dictionary Review Committee, who recommend that COMCIFS formally
approve this release. All members of this mailing list are welcome
to comment on the draft, but VOTING MEMBERS (I. D. Brown, H. M. Berman,
H. J. Bernstein, R. W. Grosse-Kunstleve, S. R. Hall, G. Madariaga,
B. McMahon and J. Westbrook) ARE REQUIRED TO SUBMIT A FORMAL VOTE for
or against the new version.

PLEASE SUBMIT YOUR VOTE BY JANUARY 20th 2008.

A complete draft of the dictionary incorporating these revisions may
be inspected at

ftp://ftp.iucr.org/cifdics/draft_cif_core_2.4.dic

with formatted versions (PDF and HTML respectively) at

ftp://ftp.iucr.org/cifdics/draft_core2.4.pdf
http://www.iucr.org/iucr-top/cif/cifdic_html/1/cif_core_draft2.4.dic/index.html

If this version is approved, the relevant Chapters of International
Tables for Crystallography Volume G (Online) will be updated to
reflect and describe the new content.

Best wishes
Brian McMahon
Coordinating Secretary

#========================================================================
PROPOSED CHANGES IN CIF CORE DICTIONARY VERSION 2.4

   2007-12-04 BMcM: Fixed typo in equation appearing in
                    _diffrn_reflns_av_sigmaI/netI and
                    _diffrn_reflns_av_unetI/netI
   2007-12-04  IDB: Added new items approved by coreDMG:
                    SUMMARY

                    1.  _atom_sites_solution_
                        Added new flags notdet, dual, other (Bruce Noll)

                    2.  _chemical_enantioexcess_
                        Added items *_bulk, *_bulk_technique, *_crystal,
                        *_crystal_technique (H. D. Flack)

                    3.  _diffrn_..._measured_fraction_
                        Added sentences to definitions of
                        _diffrn_reflns_resolution_full, *_theta_max and
                        *_resolution_max. Added new data items
                        _diffrn_reflns_Laue_measured_fraction_full, *_max
                        _diffrn_reflns_point_group_measured_fraction_full
                        and *_max

                    4.  _diffrn_standards_decay_%
                        Clarified definition and added examples.

                    5.  _distributed_density_
                        Added _atom_site_distributed_density_id and the new
                        DISTRIBUTED_DENSITY category following suggestions
                        from David Watkin.

                    6.  _exptl_absorption_correction_T_max, *_T_min
                        Clarified definition and added items
                        exptl_transmission_factor_max and *_min

                    7.  _geom_bond_multiplicity
                        New data item added.

                    8.  _publ_section_keywords
                        New data name added.

                    9.  _refine_ls_F_calc
                        Added _refine_ls_F_calc_details, *_formula and
                        *_precision.

                    10. _symmetry_equiv
                        Added _enumeration_default 1 to _space_group_symop_id
                        and _symmetry_equiv_pos_site_id; added
                        _enumeration_default x,y,z to
                        _symmetry_equiv_pos_as_xyz; added comment about the
                        need to have the identity as symop 1 to
                        _space_group_symop_operation_xyz, _space_group_symop_id,
                        _symmetry_equiv_pos_as_xyz and
                        _symmetry_equiv_pos_site_id

#------------------------------------------------------------------------
PROPOSED NEW DATA ITEMS:
#------------------------------------------------------------------------

data_atom_site_distributed_density_id
    _name                      '_atom_site_distributed_density_id'
    _category                    atom_site
    _type                        char
    _list                        yes
    _list_reference            '_atom_site_label'
    _list_mandatory              no
    _list_link_parent          '_distributed_density_id'
    _example                     an1
    _example_detail            'see example in category DISTRIBUTED_DENSITY'
    _definition
;              An identifier that links the atom defined by _atom_site_label
               with the distributed density of this atom defined in the
               DISTRIBUTED_DENSITY category.  

               Note that all the atoms that give rise to a particular
               distributed density, e.g. a ring, should be included in the
               ATOM_SITE list, even when they, or the centroid of the
               distribution, lie on a special position. That is, the
               crystallographic site symmetry of the distribution is not
               used to generate the full distributed density shape from the
               crystallographic asymmetric portion.

               The value of _atom_site_symmetry_multiplicity should be chosen
               so that for each of the atoms in the ATOM_SITE list 
               (_atom_site_occupancy)*(_atom_site_symmetry_multiplicity) is
               equal to its contribution to
               (_chemical_formula_sum)*(_cell_formula_units_Z).
;

data_chemical_enantioexcess_bulk
    _name                      '_chemical_enantioexcess_bulk'
    _category                    chemical
    _type                        numb
    _type_conditions             esd
    _enumeration_range           0.0:1.0
    _units                       .
    _units_detail                dimensionless
    _definition
;              The enantioexcess of the bulk material from which the 
               crystals were grown. A value of 0.0 indicates the
               racemate. A value of 1.0 indicates that the compound
               is enantiomerically pure.

               Enantioexcess is defined in the IUPAC Recommendations
               (Moss et al., 1996). The composition of the crystal
               and bulk must be the same.

               Ref: Moss G. P. et al. (1996). Basic Terminology of
                    Stereochemistry. Pure Appl. Chem., 68, 2193-2222.
                    http://www.chem.qmul.ac.uk/iupac/stereo/index.html 
;

data_chemical_enantioexcess_bulk_technique
    _name                      '_chemical_enantioexcess_bulk_technique'
    _category                    chemical
    _type                        char
    loop_ _enumeration
          _enumeration_detail    OA
;                                     Enantioexcess determined by
                                      measurement of the specific rotation
                                      of the optical activity of the bulk
                                      compound in solution.
;
                                 CD
;                                     Enantioexcess determined by
                                      measurement of the visible/near UV
                                      circular dichroism spectrum of the
                                      bulk compound in solution.
;
                                 EC
;                                     Enantioexcess determined by
                                      enantioselective chromatography of
                                      the bulk compound in solution.
;
                                 other
;                                     Enantioexcess determined by 
                                      a technique not included elsewhere
                                      in this list.
;
    _definition
;              The experimental technique used to determine the
               enantioexcess of the bulk compound.
;

data_chemical_enantioexcess_crystal
    _name                      '_chemical_enantioexcess_crystal'
    _category                    chemical
    _type                        numb
    _type_conditions             esd
    _enumeration_range           0.0:1.0
    _units                       .
    _units_detail                dimensionless
    _definition
;              The enantioexcess of the crystal used for the diffraction
               study. A value of 0.0 indicates the racemate. A value of
               1.0 indicates that the crystal is enantiomerically pure.

               Enantioexcess is defined in the IUPAC Recommendations
               (Moss et al., 1996).

               Ref: Moss G. P. et al. (1996). Basic Terminology of
                    Stereochemistry. Pure Appl. Chem., 68, 2193-2222.
                    http://www.chem.qmul.ac.uk/iupac/stereo/index.html 
;


data_chemical_enantioexcess_crystal_technique
    _name                      '_chemical_enantioexcess_crystal_technique'
    _category                    chemical
    _type                        char
    loop_ _enumeration
          _enumeration_detail    CD
;                                     Enantioexcess determined by
                                      measurement of the visible/near UV
                                      circular dichroism spectrum of the
                                      crystal taken into solution.
;
                                 EC
;                                     Enantioexcess determined by
                                      enantioselective chromatography of
                                      the crystal taken into solution.
;
                                 other
;                                     Enantioexcess determined by 
                                      a technique not included elsewhere
                                      in this list.
;
    _definition
;              The experimental technique used to determine the
               enantioexcess of the crystal.
;


data_diffrn_reflns_Laue_measured_fraction_full
    _name                      '_diffrn_reflns_Laue_measured_fraction_full'
    _category                    diffrn_reflns         
    _type                        numb
    _related_item              '_diffrn_measured_fraction_theta_full'    
    _related_function            alternate
    _enumeration_range           0.95:1.0
    _definition
;              Fraction of Laue unique reflections (symmetry-independent in
               the Laue group) measured out to the resolution given in
               _diffrn_reflns_resolution_full or _diffrn_reflns_theta_full.
               The Laue group always contains a centre of symmetry so that
               the reflection h,k,l is always equivalent to the reflection
               -h,-k,-l even in space groups without a centre of symmetry.
               This number should not be less than 0.95, since it represents
               the fraction of reflections measured in the part of the
               diffraction pattern that is essentially complete.
;

data_diffrn_reflns_Laue_measured_fraction_max
    _name                      '_diffrn_reflns_Laue_measured_fraction_max'
    _category                    diffrn_reflns   
    _type                        numb
    _related_item              '_diffrn_measured_fraction_theta_max'
    _related_function            alternate
    _enumeration_range           0:1.0
    _definition
;              Fraction of Laue unique reflections (symmetry-independent in
               the Laue group) measured out to the resolution given in
               _diffrn_reflns_resolution_max or _diffrn_reflns_theta_max.
               The Laue group always contains a centre of symmetry so that the
               reflection h,k,l is always equivalent to the reflection -h,-k,-l
               even in space groups without a centre of symmetry.
;

data_diffrn_reflns_point_group_measured_fraction_full
    _name                    '_diffrn_reflns_point_group_measured_fraction_full'
    _category                    diffrn_reflns         
    _type                        numb
    _related_item              '_diffrn_measured_fraction_theta_full'    
    _related_function            alternate
    _enumeration_range           0.95:1.0
    _definition
;              Fraction of crystal point-group unique reflections (i.e.
               symmetry-independent in the crystal point group) measured
               out to the resolution given in _diffrn_reflns_resolution_full
               or _diffrn_reflns_theta_full. For space groups that do not
               contain a centre of symmetry the reflections h,k,l and
               -h,-k,-l are independent. This number should not be less
               than 0.95, since it represents the fraction of reflections
               measured in the part of the diffraction pattern that is
               essentially complete.
;

data_diffrn_reflns_point_group_measured_fraction_max
    _name                    '_diffrn_reflns_point_group_measured_fraction_max'
    _category                    diffrn_reflns   
    _type                        numb
    _related_item              '_diffrn_measured_fraction_theta_max'
    _related_function            alternate
    _enumeration_range           0:1.0
    _definition
;              Fraction of crystal point-group unique reflections (i.e.
               symmetry-independent in the crystal point group) measured
               out to the resolution given in _diffrn_reflns_resolution_max
               or _diffrn_reflns_theta_max. For space groups that do not
               contain a centre of symmetry the reflections h,k,l and
               -h,-k,-l are independent.
;

               reflection count is close to complete. The fraction of unique
               reflections measured out to this angle is given by
               _diffrn_measured_fraction_theta_full.
               diffraction pattern. The fraction of unique reflections
               measured out to this angle is given by
               _diffrn_measured_fraction_theta_max
               The fraction of unique reflections measured out to this angle
               is given by _diffrn_measured_fraction_theta_max

#########################
## DISTRIBUTED_DENSITY ##
#########################
data_distributed_density_[]
    _name                      '_distributed_density_[]'
    _category                    category_overview
    _type                        null
    loop_ _example
          _example_detail
# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
;
    loop_
    _atom_site_label
    _atom_site_type_symbol
    _atom_site_fract_x
    _atom_site_fract_y
    _atom_site_fract_z
    _atom_site_U_iso_or_equiv
    _atom_site_occupancy
    _atom_site_symmetry_multiplicity
    _atom_site_adp_type
    _atom_site_distributed_density_id
    _atom_site_calc_flag
     # Inner ring of cyclopentadiene carbon atoms and borazole
     C1   C -0.1362(8) -0.0974(8) -0.3116(10) 0.0662(18) 0.625(1) 4 Uiso .   d
     C2   C -0.1060(8) -0.2165(8) -0.1837(10) 0.071(2)   0.625(1) 4 Uiso .   d
     C3   C -0.1774(9) -0.1939(9) -0.0820(11) 0.082(2)   0.625(1) 4 Uiso .   d
     C4   C -0.2529(9) -0.0561(9) -0.1479(12) 0.084(2)   0.625(1) 4 Uiso .   d
     C5   C -0.2261(8) -0.0002(8) -0.2891(10) 0.072(2)   0.625(1) 4 Uiso .   d
     C1a  C   .          .          .          .         0.208(1) 4 .    an1 dum
     C2a  C   .          .          .          .         0.208(1) 4 .    an1 dum
     C3a  C   .          .          .          .         0.208(1) 4 .    an1 dum
     C4a  C   .          .          .          .         0.208(1) 4 .    an1 dum
     C5a  C   .          .          .          .         0.208(1) 4 .    an1 dum
     N1   N -0.1375(8) -0.0968(8) -0.3201(10) 0.065(2)   0.167(1) 4 Uiso .   d
     B1   B -0.1002(8) -0.2265(8) -0.1728(10) 0.071(2)   0.167(1) 4 Uiso .   d
     N2   N -0.1402(8) -0.1034(8) -0.0765(10) 0.076(2)   0.167(1) 4 Uiso .   d
     B2   B -0.2370(9) -0.0364(9) -0.1832(10) 0.085(2)   0.167(1) 4 Uiso .   d
     N3   N -0.2893(8)  0.0034(8) -0.3621(10) 0.062(2)   0.167(1) 4 Uiso .   d
     B3   B -0.2246(9) -0.0452(9) -0.3004(11) 0.073(2)   0.167(1) 4 Uiso .   d
     # Outer ring of methyl groups
     C11  C -0.0951    -0.0733    -0.4330     0.1901     0.625(1) 4 Uani .   d
     C12  C -0.0272    -0.3236    -0.1750     0.1990     0.625(1) 4 Uani .   d
     C13  C -0.1719    -0.2833     0.0404     0.2483     0.625(1) 4 Uani .   d
     C14  C -0.3291    -0.0080    -0.0844     0.2450     0.625(1) 4 Uani .   d
     C15  C -0.2817     0.1218    -0.3770     0.2219     0.625(1) 4 Uani .   d
     C11a C   .          .          .          .         0.208(1) 4 .    an2 dum
     C12a C   .          .          .          .         0.208(1) 4 .    an2 dum
     C13a C   .          .          .          .         0.208(1) 4 .    an2 dum
     C14a C   .          .          .          .         0.208(1) 4 .    an2 dum
     C15a C   .          .          .          .         0.208(1) 4 .    an2 dum

    # Details of the two rings of distributed density are given
    # in the following loop
    loop_
    _distributed_density_id
    _distributed_density_shape
    _distributed_density_position_x
    _distributed_density_position_y
    _distributed_density_position_z
    _distributed_density_radius
    _distributed_density_direction_h
    _distributed_density_direction_k
    _distributed_density_direction_l
    _distributed_density_Uiso
    _distributed_density_symmetry_multiplicity
    an1 ring -0.1810(8)  -0.1133(8)  -0.2058(8)    
                  1.198(6)    1.35(2) 0.07(2) -0.45(2)   0.052(2)   4
    an2 ring -0.1873(14) -0.1156(14) -0.2210(2)
                  2.626(6)    1.30(2) 0.10(2) -0.40(2)   0.131(3)   4
;
;
    Example 1 - This example is fictitious (and chemically implausible) but
                it is designed to illustrate how a complex system of
                distributed density can be recorded. In this example
                pentamethyl cyclopentadiene (Cp*) and borazole occupy the
                same location in the crystal in the ratio 5:1. The atoms
                of the borazole ring are fixed as are three quarters of
                the atoms in the Cp* ring, but the remaining quarter of
                the Cp* molecules are freely rotating around the cylindrical
                Cp* axis.  The rotating Cp* molecules give rise to two
                concentric rings of density, one from the atoms in the
                ring and the other from the methyl groups (hydrogen atoms
                are ignored). On top of these rings lie the atoms of the
                fixed Cp* molecules.  The atoms of the borazole molecule also
                lie over the inner Cp* ring. Full details of the chemical
                composition are given in the ATOM_SITE loop together with
                the positions of the fixed atoms. The coordinates of the
                atoms that give rise to the distributed ring of density
                are set to '.', meaning that they have no significance as
                the atoms are dummy atoms. They are included to give the
                correct composition when _atom_site_occupancy and
                _atom_site_symmetry_multiplicity are given. The composition
                defined in the ATOM_SITE loop is linked to the
                DISTRIBUTED_DENSITY loop through the parent-child
                identifiers, 'an1' and 'an2' (for annulus 1 and 2). The
                one quarter of the Cp* molecules that are rotating have
                the occupation number of 0.208 = 2/24 = 5/6 (the total
                occupancy of the Cp*) x 1/4 (the portion rotating).

                The three quarters that are in fixed positions have the
                occupation number of 0.625 = 15/24 = 5/6 x 3/4. 
;
# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    _definition
;              Data items in the distributed_density category describe the
               geometric arrangement of an atom or atoms when they are
               distributed uniformly over a line or surface such as a ring,
               cylindrical shell or spherical shell, the line or surface being
               given a thickness through the application of an atomic
               displacement parameter.
;

data_distributed_density_details
    _name             '_distributed_density_details'
    _category          distributed_density
    _type              char
    _list              both
    _list_reference    '_distributed_density_id'
    _example            
;              The distribution was modelled using a disc of 
               density of the given radius.
;
    _definition
;              Information about the distribution of density not
               given in other items.
;

data_distributed_density_direction_
    loop_ _name                '_distributed_density_direction_h'
                               '_distributed_density_direction_k'
                               '_distributed_density_direction_l'
    _category                    distributed_density
    _type                        numb
    _type_conditions             esd
    _list                        both
    _list_reference              '_distributed_density_id'
    _units                       rlu
    _units_detail              'reciprocal lattice units'
    _definition
;              The (covariant) components on a reciprocal-lattice basis
               of a vector of arbitrary length used to indicate the
               direction of the unique axis of the distribution,
               e.g. the axis of a cylindrical shell or the normal
               to the plane of a ring.
;

data_distributed_density_id
    _name                      '_distributed_density_id'
    _category                    distributed_density
    _type                        char  
    _list                        both
    _list_mandatory              yes
    _list_link_child           '_atom_site_distributed_density_id'
    _definition
;              An identifier that links the atom defined by 
               _atom_site_label with a distributed density
               defined in the DISTRIBUTED_DENSITY category.         
;

data_distributed_density_length
    _name                      '_distributed_density_length'
    _category                    distributed_density
    _type                        numb
    _type_conditions             esd
    _list                        both
    _list_reference            '_distributed_density_id'
    _enumeration_range            0.0:
    _units                       A
    _units_detail              'Angstrom units'
    _definition
;              The length of the line or cylindrical shell of distributed
               density in angstroms. 
;

data_distributed_density_position_
    loop_ _name                '_distributed_density_position_x'
                               '_distributed_density_position_y'
                               '_distributed_density_position_z'
    _category                    distributed_density
    _type                        numb
    _type_conditions             esd
    _list                        both
    _list_reference            '_distributed_density_id'
    _definition
;              The position of the centroid of the distributed density in
               fractions of the unit cell values.
;

data_distributed_density_radius
    _name                      '_distributed_density_radius'
    _category                    distributed_density
    _type                        numb
    _type_conditions             esd
    _list                        both
    _list_reference            '_distributed_density_id'
    _enumeration_range           0.0:
    _units                       A
    _units_detail              'Angstrom units'
    _definition
;              The radius of the ring, or of the cylindrical or spherical
               shell, of distributed density in angstroms.
;

data_distributed_density_shape
    _name                      '_distributed_density_shape'
    _category                    distributed_density
    _type                        char
    _list                        both
    _list_reference            '_distributed_density_id'
    loop_ _enumeration 
          _enumeration_detail 
                                 line        'line segment'
                                 infline
;                                             infinite line running through
                                              the crystal
;
                                 ring        'circular ring'
                                 cylshell
;                                             cylindrical shell of finite length
;
                                 infcylshell
;                                             cylindrical shell running through
                                              the crystal
;
                                 sphereshell 'spherical shell'
                                 other
;                                             give details in
                                              _distributed_density_details
;
    _definition
;              A flag that indicates the shape of the distributed density. 
               The lines and ring are one-dimensional distributions of
               atoms and the cylindrical shell and spherical shell are
               two-dimensional distributions.  

               In each case the root-mean-square thickness of the distribution
               is given by the atomic displacement parameter defined in
               _distributed_density_Uiso.
;

data_distributed_density_symmetry_multiplicity
    _name                      '_distributed_density_symmetry_multiplicity'
    _category                    distributed_density   
    _type                        numb
    _list                        both
    _list_reference            '_distributed_density_id'
    _enumeration_range            1:192
    _definition
;              The number of images of the centroid of the distributed density
               that the space-group symmetry generates in the unit cell
               reported in the CELL category.  It is the number that
               appears in International Tables for Crystallography Vol. A
               (2002) for the Wyckoff position occupied by the centroid. 

               In this treatment the symmetry of the distribution itself is
               ignored, including any operations of its point group that are
               part of the crystallographic site symmetry of the centroid.     
               All the atoms that give rise to the distributed density should
               therefore be listed in the ATOM_SITE category even if they, or
               the centroid of the distribution, lie on crystallographic
               special positions.

               For example, if the distribution is a ring and the centroid
               of the ring lies on a crystallographic mirror plane, all
               the atoms in the ring are listed if the ring lies either in or
               perpendicular to the mirror plane since the mirror image of
               the ring lies over the ring itself. If the ring is at some
               arbitrary angle to the mirror plane, the mirror generates
               a second ring and both rings should be described independently.  
               However, because both rings cannot be simultaneously occupied,
               the occupation numbers given in the ATOM_SITE category must
               have a value equal to or less than 0.5. 
;

data_distributed_density_Uiso
    _name                      '_distributed_density_Uiso'
    _category                    distributed_density        
    _type                        numb
    _type_conditions             esd
    _list                        both
    _list_reference            '_distributed_density_id'
    _enumeration_range           0.0:
    _units                       A^2^
    _units_detail              'Angstrom units squared'
    _example                     0.018(3)
    _definition
;              The factor exp(-Ux^-2^) is applied to all parts of the
               distribution, where U = _distributed_density_Uiso and
               x is the distance from the ideal one- or two-dimensional
               shape. This emulates the effects of thermal motion or
               static displacement from the ideal positions described in this
               category and has the effect of converting the simple one-
               or two-dimensional geometric shapes into three-dimensional
               objects of mean square thickness U.
;


data_exptl_transmission_factor_max
    _name                      '_exptl_transmission_factor_max'
    _category                    exptl        
    _type                        numb        
    _type_conditions             su        
    _enumeration_range           0.0:1.0
    _definition
;              The calculated maximum value of the transmission factor for
               the specimen. Its value does not include the effects of
               absorption in the specimen mount. The presence of this
               item does not imply that the structure factors have been
               corrected for absorption. The applied correction should be 
               given by _exptl_absorpt_correction_T_max.
;

data_exptl_transmission_factor_min
    _name                     '_exptl_transmission_factor_min'
    _category                    exptl        
    _type                        numb        
    _type_conditions             su        
    _enumeration_range           0.0:1.0
    _definition
;              The calculated minimum value of the transmission factor for
               the specimen. Its value does not include the effects of
               absorption in the specimen mount. The presence of this
               item does not imply that the structure factors have been
               corrected for absorption. The applied correction should be 
               given by _exptl_absorpt_correction_T_min.
;

data_geom_bond_multiplicity
    _name                      '_geom_bond_multiplicity'
    _category                    geom_bond        
    _type                        numb        
    _list                        yes        
    _list_reference            '_geom_bond_atom_site_label_'    
    _enumeration_range           0:
    _enumeration_default         1
    _definition
;              The number of times the given bond appears in the environment
               of the atoms labelled _geom_bond_atom_site_label_1. In cases
               where the full list of bonds is given, one of the series of
               equivalent bonds may be assigned the appropriate multiplicity
               while the others are assigned a value of 0.
;

data_refine_ls_F_calc_details
    _name                      '_refine_ls_F_calc_details'
    _category                    refine
    _type                        char
    loop_ _example               'Gaussian integration using 16 points'
;                                Bessel functions expansion up to 5th order.
                                 Bessel functions estimated accuracy: better
                                 than 0.001 electrons.
;
    _definition
;              Details concerning the evaluation of the structure
               factors using the expression given in
               _refine_ls_F_calc_formula.
;

data_refine_ls_F_calc_formula
    _name                      '_refine_ls_F_calc_formula'
    _category                    refine
    _type                        char
    _definition
;              Analytical expression used to calculate the structure factors.  
;

data_refine_ls_F_calc_precision
    _name                      '_refine_ls_F_calc_precision'
    _category                    refine
    _type                        numb
    _enumeration_range           0.0:
    _definition
;              This item gives an estimate of the precision resulting
               from the numerical approximations made during the evaluation
               of the structure factors using the expression given in
               _refine_ls_F_calc_formula following the method outlined
               in _refine_ls_F_calc_details.  For X-ray diffraction the
               result is given in electrons.
;

#========================================================================
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