Unrestrained SDPD future
Dear colleagues, Since the restrained SDPD future has been announced in the respective list without a chance to go back: http://tech.groups.yahoo.com/group/sdpd/message/3016 It's my turn to put forward an alternative unrestrained variant that seems a bit more interesting and not so hopeless, IMHO. This variant consists in a more accurate approach to the experiment and the modeling instead of compensating the inaccuracy by restraints. In the discussion of the restrained Rietveld: http://dx.doi.org/10.1107/S1600536813017522 proposed as an instance of the SDPD future trend, I presented an unrestrained variant of the refinement: http://tech.groups.yahoo.com/group/sdpd/message/3023 and noted that Future improvements are possible if one exerts further efforts to the sample preparation, measurements and the refinement model adjustment. Spending an extra couple of hours for the data analysis, an additional micro-admixture has been identified whose inclusion into the model resulted in further notable improvements of the structure geometry: http://sites.google.com/site/ddmsuite/home/vn2075-DDM.cif http://sites.google.com/site/ddmsuite/home/vn2075-DDM.png Characteristic distances and their expectations: Pos. Dist. Exp. Co-O1 1.92(2) 1.91 Co-O2 1.94(2) 1.91 Co-N1 1.98(1) 1.96 Co-N2 1.95(2) 1.96 Co-N3 1.92(2) 1.96 Co-N4 1.99(1) 1.96 C1-O1 1.31(4) 1.32 C1-O2 1.34(4) 1.32 C1-O3 1.25(3) 1.23 N5-O4 1.27(3) 1.24 N5-O5 1.23(3) 1.24 N5-O6 1.25(3) 1.24 All distances and intramolecular angles are in agreement with the expected values within their uncertainties. Future improvements are still possible, being determined mostly by the sample preparation and measurements now. Of course, in REALLY complex and HOPELESS cases a minimal number of constraints may be imposed if the refinement convergence of atomic positions is REALLY impossible without them. In the above example, rigid constraints were imposed on H-atoms, which is, though, not always necessary. The use of soft restraints should be avoided as much as possible since a generally acceptable methodology of their safe application has not been developed yet. Best unrestrained regards, Leonid *** Leonid A. Solovyov Institute of Chemistry and Chemical Technology 660049, K. Marx 42, Krasnoyarsk, Russia http://sites.google.com/site/solovyovleonid ***++ Please do NOT attach files to the whole list alan.he...@neutronoptics.com Send commands to lists...@ill.fr eg: HELP as the subject with no body text The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/ ++
Re: Unrestrained SDPD future
http://dx.doi.org/10.1107/S1600536813017522 proposed as an instance of the SDPD future trend Fortunately this short paper is open access. http://journals.iucr.org/e/issues/2013/07/00/vn2075/vn2075.pdf It is truly a tour de force to quote N-H bonds determined to 3 significant figures from a heavy atom compound with one axis as long as 17.5 Angstroms - by x-ray powder diffraction ! The future isn't what it used to be (Paul Valery, French poet) Alan __ Dr Alan Hewat, NeutronOptics, Grenoble, FRANCE alan.he...@neutronoptics.com +33.476.98.41.68 http://www.NeutronOptics.com/hewat __ ++ Please do NOT attach files to the whole list alan.he...@neutronoptics.com Send commands to lists...@ill.fr eg: HELP as the subject with no body text The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/ ++
Re: Unrestrained SDPD future
Hello everybody, the fact than many papers presenting results where refinements are flooded by tsunami of restraints appear, is main responsibility of referees and editors. For instance, CIF dictionary clearly defines restraints items, but they do not appear in many published CIF's. Good question is if standard refinement program generate these item in their CIF outputs. I would also end with a quote, if you don't mind. Here it is : Common sense is not so common (attributed to Voltaire, but I guess this problem was common even in ancient Egypt even if not before ...) lubo On Fri, 9 Aug 2013, Alan Hewat wrote: http://dx.doi.org/10.1107/S1600536813017522 proposed as an instance of the SDPD future trend Fortunately this short paper is open access. http://journals.iucr.org/e/issues/2013/07/00/vn2075/vn2075.pdf It is truly a tour de force to quote N-H bonds determined to 3 significant figures from a heavy atom compound with one axis as long as 17.5 Angstroms - by x-ray powder diffraction ! The future isn't what it used to be (Paul Valery, French poet) Alan __ Dr Alan Hewat, NeutronOptics, Grenoble, FRANCE alan.he...@neutronoptics.com +33.476.98.41.68 http://www.NeutronOptics.com/hewat __ ++ Please do NOT attach files to the whole list alan.he...@neutronoptics.com Send commands to lists...@ill.fr eg: HELP as the subject with no body text The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/ ++
Re: [sdpd] Unrestrained SDPD future
As some people from the PRC reported that they can't see the files at Google due to Govern-Mental restrictions I put them into the SDPD-group folder: http://tech.groups.yahoo.com/group/sdpd/files/vn2075-DDM.cif http://tech.groups.yahoo.com/group/sdpd/files/vn2075-DDM.png Restraints are everywhere!-) *** Leonid A. Solovyov Institute of Chemistry and Chemical Technology 660049, K. Marx 42, Krasnoyarsk, Russia http://sites.google.com/site/solovyovleonid *** From: Leonid Solovyov l_solov...@yahoo.com To: s...@yahoogroups.com s...@yahoogroups.com Cc: rietveld_l@ill.fr rietveld_l@ill.fr Sent: Friday, August 9, 2013 2:22 PM Subject: [sdpd] Unrestrained SDPD future Dear colleagues, Since the restrained SDPD future has been announced in the respective list without a chance to go back: http://tech.groups.yahoo.com/group/sdpd/message/3016 It's my turn to put forward an alternative unrestrained variant that seems a bit more interesting and not so hopeless, IMHO. This variant consists in a more accurate approach to the experiment and the modeling instead of compensating the inaccuracy by restraints. In the discussion of the restrained Rietveld: http://dx.doi.org/10.1107/S1600536813017522 proposed as an instance of the SDPD future trend, I presented an unrestrained variant of the refinement: http://tech.groups.yahoo.com/group/sdpd/message/3023 and noted that Future improvements are possible if one exerts further efforts to the sample preparation, measurements and the refinement model adjustment. Spending an extra couple of hours for the data analysis, an additional micro-admixture has been identified whose inclusion into the model resulted in further notable improvements of the structure geometry: http://sites.google.com/site/ddmsuite/home/vn2075-DDM.cif http://sites.google.com/site/ddmsuite/home/vn2075-DDM.png Characteristic distances and their expectations: Pos. Dist. Exp. Co-O1 1.92(2) 1.91 Co-O2 1.94(2) 1.91 Co-N1 1.98(1) 1.96 Co-N2 1.95(2) 1.96 Co-N3 1.92(2) 1.96 Co-N4 1.99(1) 1.96 C1-O1 1.31(4) 1.32 C1-O2 1.34(4) 1.32 C1-O3 1.25(3) 1.23 N5-O4 1.27(3) 1.24 N5-O5 1.23(3) 1.24 N5-O6 1.25(3) 1.24 All distances and intramolecular angles are in agreement with the expected values within their uncertainties. Future improvements are still possible, being determined mostly by the sample preparation and measurements now. Of course, in REALLY complex and HOPELESS cases a minimal number of constraints may be imposed if the refinement convergence of atomic positions is REALLY impossible without them. In the above example, rigid constraints were imposed on H-atoms, which is, though, not always necessary. The use of soft restraints should be avoided as much as possible since a generally acceptable methodology of their safe application has not been developed yet. Best unrestrained regards, Leonid *** Leonid A. Solovyov Institute of Chemistry and Chemical Technology 660049, K. Marx 42, Krasnoyarsk, Russia http://sites.google.com/site/solovyovleonid *** [Non-text portions of this message have been removed] __._,_.___ Reply via web post Reply to sender Reply to group Start a New Topic Messages in this topic (1) Recent Activity: Visit Your Group Switch to: Text-Only, Daily Digest • Unsubscribe • Terms of Use • Send us Feedback . __,_._,___ ++ Please do NOT attach files to the whole list alan.he...@neutronoptics.com Send commands to lists...@ill.fr eg: HELP as the subject with no body text The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/ ++
