At the end it is all wrong as we don’t refine individual electrons but restrained groups that are called “atoms” which are extrapolated with some average function calculated for free, unbounded atom.
Peter Zavalij From: rietveld_l-requ...@ill.fr [mailto:rietveld_l-requ...@ill.fr] On Behalf Of Leonid Solovyov Sent: Thursday, August 01, 2013 7:33 PM To: s...@yahoogroups.com Cc: rietveld_l@ill.fr Subject: Re: [sdpd] Re: Are restraints as good as observations ? >What information capacity ? The fact is that imposing > the expected values you obtain a similar fit. This tells > you that you cannot discuss your unrestrained "information", > because it is unreliable. > Information is something you may discuss reliably. > The only possible discussion about P3-O14 = 1.72(3)A > is to say that it is very probably strongly overestimated. After THIS unrestrained refinement one CAN discuss RELIABLY ALL interatomic distances including P-O, K-O, K-P, K-K and P-P, as well as angles, orientations etc., WITHIN THEIR UNCERTAINTIES that are also estimated RELIABLY according to the EXPERIMENTALLY DETERMINED deviations of the unrestrained P-O distances. After the restrained refinement NOTHING can be discussed RELIABLY since neither the values nor their uncertainties are determined EXPERIMENTALLY. After the unrestrained refinement one can state RELIABLY that the structure is DETERMINED with definite precision and, thus, discuss its features, compare it with other experimentally determined structures within their uncertainties, make more or less definite conclusions etc. After the restrained refinement one can only state that a hypothetical structure model is proposed and NOTHING can be concluded or discussed RELIABLY. Don't you see the difference??!! Determination = reliable experimental evaluation + reliable estimation of uncertainties. Now I probably understand your "colleagues". ******************************************************* Leonid A. Solovyov Institute of Chemistry and Chemical Technology 660049, K. Marx 42, Krasnoyarsk, Russia http://sites.google.com/site/solovyovleonid ******************************************************* ________________________________ From: Armel Le Bail <x...@noos.fr<mailto:x...@noos.fr>> To: s...@yahoogroups.com<mailto:s...@yahoogroups.com> Cc: rietveld_l@ill.fr<mailto:rietveld_l@ill.fr> Sent: Friday, August 2, 2013 12:40 AM Subject: Re: [sdpd] Re: Are restraints as good as observations ? > All deviations from expected values (1.514 and 1.634) are within 3 e.s.u.s > that are around 0.03 A in average. Further improvements seem possible, but it > will require more time and efforts. > > So, one more example of underestimated information capacity of powder data > and overestimated necessity of restraints. What information capacity ? The fact is that imposing the expected values you obtain a similar fit. This tells you that you cannot discuss your unrestrained "information", because it is unreliable. Information is something you may discuss reliably. The only possible discussion about P3-O14 = 1.72(3)A is to say that it is very probably strongly overestimated. Such are powder results for complex cases. Sure, the restrained distances cannot be discussed as well. At least they are not completely extravagant. Best Armel
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