RE: Phase ID draft report
- To: "A Working Group of the IUCr Commission on Crystallographic Nomenclature" <phase-identifiers@iucr.org>
- Subject: RE: Phase ID draft report
- From: "S. C. Abrahams" <sca@mind.net>
- Date: Wed, 5 May 2004 11:06:12 -0700
- Importance: Normal
- In-Reply-To: <407FFEDB.10007@mcmaster.ca>
Dear
David:
Many
thanks for your April 16 draft. My comments follow:
1. I have noted and am in general
agreement with the new additions made since the last draft. I do, however, have
a number of suggested corrections (in red) as
follows.
2. “1. INTRODUCTION”
Modify
first paragraph, third sentence, to read “As the only such
convention already approved by the CCN on phase transition
nomenclature
(Tolédano
et al, 1998, 2001) is not readily
adaptable for electronic use, the CCN established the Working Group on
Crystalline Phase Identifiers to make recommendations that could be of use to
the IChI working group.”
Change
the second
paragraph, final
sentence, to read: “Our
recommendations are therefore cast in the form of additions to IChI, in the
knowledge that the resulting identifier can be as readily used by the
crystallographic as by the chemical community.”
3. In “2. TERMS OF REFERENCE OF THE WORKING
GROUP”,
Change the first
sentence to read: “The Working Group was charged with
recommending to the IUCr
Commission on Crystallographic Nomenclature:”
Change the second
sentence charge to read “2. The best way in which
this identifier can be implemented, including its incorporation in the CCN
recommended phase transition nomenclature.”
Change
“working
group” in the final
sentence of section “2” to “Working Group”
4. In “5.1 Construction
of the IUPAC chemical identifier”
Change the second
sentence, fifth paragraph, to read “These are not part of the identifier proper
and are not
shown
here.”
5. In “6.1 Layer 5: State of
Matter”
Change the second
sentence in the paragraph after the first enumeration list to read “A crystal is
defined as a phase for
which, in principle, it is possible to assign a space group, even if that space
group is only related to the full
space group (as in the
case of
aperiodic structures).”
6. In “6.2 Layer 6: Space
Group”
Change the second
sentence in the first paragraph to read “It consists of a number between 1 and
230 that uniquely identifies the space group type except for aperiodic
crystals, cf. Jansen et al.(2002).
Change the final sentence in the
second
paragraph to read
“Quasicrystals
cannot be assigned a conventional
space group and
are best treated as a different state of matter (see Section 6.1
above).”
7. In “6.3 Layer 7. Wyckoff Sequence”
It would be more appropriate here to
use the same Wyckoff site order as used in ITA, i.e. number, followed by letter.
It would also be helpful if the example contained at least two sites with
multiplicity other than 1, so that it becomes, for example, ‘1a 2c 3f 6g’ or
‘a2c3f6g’, to avoid possible confusion with the dropped ‘1’ (which I agree
should be dropped).
Note that §6.4 is missing, so
“Possible further layers” should be labelled §6.4, not §6.5
8. In “7.2.1
Composition”, it is
appropriate to provide a clear definition of ‘tolerance factor’ if it is to be
required.
9. In “7.2.4 WS: The Wyckoff sequence”, the second
sentence should use ITA order, see item 7 above.
Change the fifth
sentence to read “The letters are
listed in alphabetic order but before determining the Wyckoff sequence, the
structure must be normalized according to the algorithm used in the program
STRUCTURE TIDY, see Parthé & Gelato
(1984, 1985), Gelato & Parthé (1987).”
[Note: all references
should be relocated under REFERENCES
at the end of the Report].
10. In “8.1 Description of the IUCr-CCN
phase transition symbol.”
Change the first
sentence in the first full paragraph to read “Recently the Commission on
Crystallographic Nomenclature of the International Union of Crystallography
adopted a Phase Transition Nomenclature (Tolédano et al., 1998,
2001) described on
the IUCr web page: http://www.iucr.org - look for Commissions/Commission on
Crystallographic Nomenclature/CNOM Onlineinformation/ /Structural
Phase Transition Nomenclature.”
Change the third
sentence in the third paragraph to read “The intent of this symbol is to include
the maximum identification
information
density
for
the phase, whereas the philosophy of IChI is to include only the minimum
information needed for phase
identification.”
Change fifth and
sixth (last) sentences to read “The combined IChI and CCN Phase
Transition Nomenclature identifier symbol
provides, in principle, all the information necessary to access the appropriate
database entries available on a given material. A method for combining the
two
is described in Section 8.3.
In “8.2.2 Iron
(Fe) (Donohue, 1974)”
Change the third
sentence, first full paragraph after the five phase entries to read “The correct
space group of untwinned alpha
(ferromagnetic)
iron
cannot be isotropic Im(bar)3m
(229) but the deviation
from higher symmetry is very small
and
the correct space group is not yet determined.”*
_________________________________
* The point group is most
likely Shubnikov group 4/mm¢m¢
but this information is not necessary
in the Report.
_________________________________
11. At the end of
the Report, add:
REFERENCES
Abrahams,
S. C., Ihringer, J., Marsh, P. & Nassau, K. (1984). J. Chem. Phys. 81,
2082-2087.
Donohue, J.
(1974). The
Structure of the Elements.
New York: John Wiley & Sons.
Gelato, L.M.,
Parthé, E. (1987). J. Appl. Cryst. 20, 139-143.
Ihringer, J. &
Abrahams, S. C. (1984)
Phys. Rev. B30, 6540-6548
(1984).
Janssen, T. ,
Birman,
J.
L., Dénoyer,
F.,
Koptsik,
V.
A., Verger-Gaugry,
J.
L., Weigel,
D.,
Yamamoto,
A.,
Abrahams, S. C. & Kopsky, V.(2002).
Acta Cryst., A58, 605-621.
Parthé, E.,
Gelato, L.M. (1984). Acta Cryst. A40,
169-183,
Parthé, E.,
Gelato, L.M. (1985). Acta Cryst. A41, 142-151.
Tolédano, J.-C.,
Glazer, A.
M., Hahn, Th., Parthe, E.,
Roth, R. S.
Berry,g R. S.,
Metselaar, R. &
Abrahams,
S. C.
(1998).
Acta
Cryst. (1998). A54,
1028-1033.
Tolédano, J.-C., Berry,
R. S., Brown,
P. J.,
Glazer,
A. M.,
Metselaar,
R., Pandey, D.,
Perez-
Mato, J. M., Roth, R. S. & Abrahams, S. C. (2001). Acta Cryst. (2001). A57, 614-626.
I look forward to seeing the comments of our other members.
With best wishes
Sidney
Prof. S. C. Abraham
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