New version of CIF Core dictionary (2.4)
Ralf W. Grosse-Kunstleve
rwgk at yahoo.com
Sun Feb 17 22:29:41 GMT 2008
Dear David,
Sorry for the late review.
I only have a few comments regarding details in the new
DISTRIBUTED_DENSITY category. See below.
Ralf
==============================================================================
data_distributed_density_symmetry_multiplicity
_enumeration_range 1:192
==============================================================================
The upper limit is rather arbitrary. It is true that the maximum
multiplicity in the Int. Tab. is 192, but when working with
group-subgroup relations (e.g. to analyze twinning) there could be
unusual situations which require settings with larger multiplicities.
I propose that the upper limit is removed.
==============================================================================
data_distributed_density_symmetry_multiplicity
_definition
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.
==============================================================================
This seems inconsistent with the general approach of only providing
non-redundant atomic data (asymmetric unit). In my working experience,
having to deal with explicit redundancy is usually cumbersome and
prone to introduce ambiguities and errors. I'd very much prefer if
the core dictionary mandated a non-redundant representation.
==============================================================================
data_distributed_density_Uiso
_definition
; The factor exp(-Ux^-2^) is applied to all parts of the
==============================================================================
^^^^
2 pi ^2^ ?
The formula for the Debye-Waller factor (atomic Uiso) is
exp(-2 pi^2^ U d^-2^)
I find it misleading that the 2 pi^2^ is folded into
_distributed_density_Uiso. For consistency, I'd change the
definition to:
exp(-2 pi^2^ Ux^-2^)
Another commonly used notation for the isotropic displacement parameter is
"beta" (greek letter), with this definition:
exp(-beta d^-2^)
This suggests the name _distributed_density_beta_iso.
However, I'd prefer to keep _distributed_density_Uiso, but with
a definition compatible with the atomic Uiso.
==============================================================================
6. _exptl_absorption_correction_T_max, *_T_min
^^^^
wrong name
exptl_transmission_factor_max and *_min
==============================================================================
^
missing underscore
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