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cif_rstr.history
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cif_rstr.history
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##############################################################################
# #
# CIF RESTRAINTS AND CONSTRAINTS DICTIONARY VERSION 1.0 #
# ----------------------------------------------------- #
# #
# This dictionary contains the names and definitions proposed for reporting #
# restraints and constraints in the Core CIF dictionary #
# #
# Copyright 2011 International Union of Crystallography #
##############################################################################
##############################################################################
# #
# Some notes on the philosophy followed in this dictionary #
# -------------------------------------------------------- #
# The items in this dictionary are designed for reporting the restraints #
# and constraints applied during the final refinement of a structure. #
# They are not intended, nor are they suitable, for use as instructions #
# to a refinement program. #
# #
# A RESTRAINT is a condition used in the refinement of a crystal structure #
# that requires one or more of the parameters of the refinement to lie #
# within a certain range. #
# #
# A CONSTRAINT is a condition used in the refinement of a crystal structure #
# that requires one or more parameters of the refinement to have a #
# specific value or be exactly equal to another refined parameter. #
# #
# The range of values allowed in a restraint is given in this dictionary #
# by a target value and a weighting parameter, the latter being the #
# expectation value of the difference between the refined value and #
# the target. Constraints are indicated by setting the weighting #
# parameter to zero. #
# #
# Restraints and constraints are handled in many different ways in different #
# programs. The actual parameters restrained are determined by the way the #
# restraint is expressed within the program, and different programs #
# express the same restraint in different ways. In this dictionary the #
# restraints are expressed in a way that is most natural to the description #
# of the crystal structure, which means that the parameters given here #
# may not correspond to the parameters that were actually restrained. #
# For example, the rigid-body constraint is expressed here by listing the #
# atoms in the rigid body. Distances and angles between them are constant. #
# For a rigid body the target parameters are the same as the refined #
# parameters, allowing the target geometry of the rigid body to be found #
# from the reported atomic coordinates. However, in order to apply #
# this constraint in a refinement, either the coordinates of the atoms #
# in some arbitrary coordinate system or a sufficient number of geometric #
# parameters of the body must be specified. Since all these methods #
# preserve the rigid body intact, it is only the result that needs to be #
# reported, not the details of the method used. In this way the description #
# of restraints and constraints has been kept as simple as possible. #
# #
# The restraints and constraints used are many and varied, and not all #
# can be given in the forms listed in this dictionary. #
# For this reason a general item _restr_special_details has been #
# provided so that a text description can be given for #
# a restraint or constraint that cannot be reported in any other way. #
# #
# Attention is drawn to existing items in the core dictionary that flag #
# whether items have been restrained or constrained: #
# _atom_site_refinement_flags_adp #
# _atom_site_refinement_flags_occupation #
# _atom_site_refinement_flags_posn #
# _atom_site_restraints #
# #
##############################################################################
data_on_this_dictionary
_dictionary_name cif_core_restraints.dic
_dictionary_version 1.0
_dictionary_update 2011-03-09
_dictionary_history
;
2009-18-10 Following consultations between the user community and
I. David Brown and Ilia Guzei, IDB started preparing this
dictionary using DDL1 by creating items
required by distance and angle restraints.
2009-12-09 IDB Completed first draft.
2010-01-13 IDB Corrected minor errors detected by IG prior to DMG review.
2010-01-14 IDB: Run through vcif by Brian McMahon and corrections made.
esd replaced by su in _type_conditions.
2010-06-03 IDB: U_ISO, U_SIMIILAR.
2010-09-15 IDB: The revised rigid body description is added.
2010-10-15 IDB: Corrections from H. Bernstein made.
2010-12-09 NJA: minor editing.
2011-01-24 BMcM: minor editing incorporating authors' final revisions.
2011-03-09 BMcM: released
;
# This dictionary describes 14 restraints some of which are also constraints.
#
# 1. Other restraint or constraint
# 2. Angle
# 3. Distance
# 4. Minimum approach of two atoms
# 5. Angles restrained to be equal
# 6. Distances restrained to be equal
# 7. Torsion angles restrained to be equal
# 8. Restrained parameter
# 9. Rigid body
# 10. Atoms lie on a plane
# 11. Torsion angle
# 12. Isotropic atom
# 13. Rigid bond
# 14. Similar atomic displacement parameters