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No attachment(s) to phase-identifiers Digest, Vol 10, Issue 1
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- Subject: No attachment(s) to phase-identifiers Digest, Vol 10, Issue 1
- From: "S. C. Abrahams" <sca@mind.net>
- Date: Fri, 25 Feb 2005 06:08:26 -0800
- In-Reply-To: <20050225120002.AF6D533B2D@dolomite.iucr.org>
Dear David: Thanks for your message updating us on the status of the Crystalline Phase Identifier final report. Unfortunately, the message came without any attachments - please resend. Sidney --------------------------- Prof . S. C. Abrahams Physics Department Southern Oregon University Ashland, OR 97520 Tel. (541) 482-7942 Fax. (541) 552-6415 -------------------------- -----Original Message----- From: phase-identifiers-bounces@iucr.org [mailto:phase-identifiers-bounces@iucr.org] On Behalf Of phase-identifiers-request@iucr.org Sent: Friday, February 25, 2005 4:00 AM To: phase-identifiers@iucr.org Subject: phase-identifiers Digest, Vol 10, Issue 1 Send phase-identifiers mailing list submissions to phase-identifiers@iucr.org To subscribe or unsubscribe via the World Wide Web, visit http://scripts.iucr.org/mailman/listinfo/phase-identifiers or, via email, send a message with subject or body 'help' to phase-identifiers-request@iucr.org You can reach the person managing the list at phase-identifiers-owner@iucr.org When replying, please edit your Subject line so it is more specific than "Re: Contents of phase-identifiers digest..." Today's Topics: 1. Crystalline Phase Identifier final report (David Brown) ---------------------------------------------------------------------- Message: 1 Date: Thu, 24 Feb 2005 16:29:25 -0500 From: David Brown <idbrown@mcmaster.ca> Subject: Crystalline Phase Identifier final report To: phase-identifiers@iucr.org Message-ID: <421E4735.1090308@mcmaster.ca> Content-Type: text/plain; charset="iso-8859-1" Dear Colleagues, Since circulating the 'final' draft of the report on the Crystalline Phase Identifier I have now heard back from all of you. Most of you approved the report but a couple of people were concerned about two points. I discuss these below and I have modified Section 7.2.4 of the report as noted. The revised wording is attached to this email. Section 7.2.4, dealing with the calculation of the Wyckoff sequence, has been significantly changed and I am afraid I have to ask you to check it and let me know if you approve. I need to hear from each one of you before the report can be submitted. John Faber raised a question about the rules concerning the composition given in Section 7.2.1. The reports suggests that in cases where the composition involves non-integral multipliers, it is only the relative composition that is important, and that when compositions are being compared they should be normalized, e.g., by setting the largest multiplier to 1.0. John was concerned that this would result in the loss of significant information about whether the compound was anion deficient or had a cation excess. It is true that such information would be lost, but that is not the purpose of the composition field which is merely to use the relative amounts of the different elements present as the first step in differentiating between different crystalline phases. Both John and Vicky Karen were concerned about the recommendation that we use the Parthe-Gelato convention for normalizing the structures before determining the Wyckoff sequence. Their concern was that the P-G choice of the unit cell and space group setting conflicted with other conventions already in use. However, we do not really have a choice because there is only one algorithm described in the literature that ensures a unique Wyckoff sequence. (We could invent our own algorithm and ensure that it adheres to a more traditional convention - but which convention?) In any case the conventions used in this algorithm are invisible to anyone wanting only to calculate a Wyckoff sequence. The P-G normalization is the only one that guarantees a unique Wyckoff sequence because it is the only one that normalizes the atomic coordinates as well as the cell and space group. There is no conflict with conventions that might be used in a database for other purposes. Neither the space group setting nor the unit cell basis that are used by the P-G algorithm are part of the proposed identifier. The new (attached) text now puts the emphasis on the algorithm rather than on the program, and it provides an explanation for those who might be concerned about the non-standard conventions used. Let me know if you need a copy of the whole report. I look forward to receiving your approval of the attached wording. David -------------- next part -------------- A non-text attachment was scrubbed... Name: DraftChanges05-02-23.rtf Type: application/rtf Size: 4465 bytes Desc: not available Url : http://scripts.iucr.org/pipermail/phase-identifiers/attachments/20050224/b47 cce4b/DraftChanges05-02-23-0001.rtf -------------- next part -------------- A non-text attachment was scrubbed... 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