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RE: Phase Identifiers.


Dear colleague:

It was a pleasure to find David's very clear position paper on the
tasks set out for the Working Group and Brian's illustrative examples of
limitations inherent in simple identification approaches awaiting my
return today. I would like to take this opportunity of welcoming you,
on behalf of the IUCr Commission on Crystallographic Nomenclature, to
membership in this Working Group. The final recommendations made on
crystallographic phase identifiers will surely influence quite strongly
our future ability to recall a wide range of information.

In this regard, I was pleased to note Brian's mention of IUPAC's IChI
project which has, as its objective, 'the establishment of a unique label
for each chemical substance for use in printed and electronic data
sources thereby enabling easier linking of diverse data compilations'.
I believe that project is mostly interested in organic materials at the
present time but plan to let the chair of IUPAC's Chemical Nomenclature
and Structure Representation Division (Alan McNaught) know that our group
has started its work in the interest of opening good communications between
them and us.

David has referred to the phase identifiers developed by the IUCr Working
Group on Phase Transition Nomenclature. For members' convenience, I attach
PDF files containing reprints of the two reports of this Working Group as
published in Acta Cryst. Adobe Reader must be installed on your PC to open
them. If you don't have a copy, it may be downloaded from:

        http://www.adobe.com/products/acrobat/readstep.html

(then "Text-only Acrobat Reader download page" followed by "Acrobat 5.0
Reader").

Bill Pearson's symbol, as noted by David, may well offer the basis for
producing unique and unambiguous phase identification symbols, if adequately
modified. A caveat here, as perhaps for all such symbols, may be the need
to allow for the possibility that a given phase may have been poorly
characterized. It would be helpful to know the frequency with which the
first
report of the crystal symmetry and/or number of atoms in the unit cell of
a new phase is later found to be in error. Perhaps the databases have
compiled
statistics on such error frequency?

I look forward to a vigorous discussion of the various matters raised by
David.

With kindest wishes.

Sidney
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Prof. S. C. Abrahams
Physics Department
Southern Oregon University
Ashland, OR 97520

Fax: (541) 552-6415   Tel: (541) 482 7942
Email: sca@mind.net
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

IUCr.Report.I.Phase.Transition.Nomenclature.pdf

IUCr.Phase.Trans.Nom. Report.II.pdf


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