large Eo's and neg. D-W factors
Greetings! I have inherited a vanadium EXAFS data set (due to a group member graduating - lucky dog!) that is giving me major fits. I am getting consistent numbers with all my fits which visually look fantastic, that is until I look at the numbers...one Debye-Waller factor is negative (a V-O path) and the Eo's are large, the V-Cl path is on the order of -20 eV, the V=O path is on the order of 17 eV, and the V-O path falling at -11 eV. ARe there any "tricks" outside of restraints or constraints that I can attempt to get more realistic values? (I understand that a large Eo can be realistic, but a negative Debye-Waller factor doesn't make sense.) I can restrain the V-O Debye-Waller factor and get a positive value, but then the V=O D-W factor is negative. If I restrain both D-W factors, the fit falls apart, suggesting something else is wrong that I just can't find. Another issue I'm having involves something in Artemis that's confusing me. Sometimes after a fit, the Artemis Pallet shows the V=O feature as the one at 1.8 Angstroms and the V-O feature at 1.6 Angstroms, completely reversed to the FEFF model. I have seen this when I separated the chlorides as well (I attempted to model the Cl at different distances as reported by Deguns, et. al. (attached) due to the immediate environment around the V in our sample being similar to the one they report in scheme 1-(I), p5008). Attached is a text file that shows an Artemis Pallet output illustrating what I'm trying to describe for the V=O and V-O paths. The Artemis project that generated the output is also attached. At this point, I'm wandering what I'm missing. Any help is greatly appreciated!! Many thanks in advance! Rich Mayes Barnes Group 450/452 Buehler Hall Dept. of Chemistry Univ. of Tennessee Knoxville, TN 37996 Project title : Fitting SA_162deglitch-merge.chi Comment : Fit #1 Prepared by : Contact : Started : 15:46:44 on 17 April, 2007 This fit at : 15:58:01 on 18 April, 2007 Environment : Artemis 0.8.007 using Windows XP, perl 5.006001, Tk 800.024, and Ifeffit 1.2.9 Figure of merit : 3 ============================================================ Independent points = 14.027343750 Number of variables = 9.000000000 Chi-square = 45.640992098 Reduced Chi-square = 9.078550099 R-factor = 0.012557807 Measurement uncertainty (k) = 0.000687372 Measurement uncertainty (R) = 0.023895029 Number of data sets = 1.000000000 Guess parameters +/- uncertainties (initial guess): enot = 17.1999060 +/- 3.4058600 (0.0000) delr = 0.1588460 +/- 0.0081480 (0.0000) ss = -0.0022720 +/- 0.0007180 (0.0030) enot_O2 = -11.0384940 +/- 9.8688920 (guessed as enot) delr_O2 = -0.2214820 +/- 0.0356500 (0.0000) ss_O2 = 0.0027560 +/- 0.0021290 (0.0030) enot_Cl = -16.0026700 +/- 3.5982940 (guessed as enot) delr_Cl = -0.0118230 +/- 0.0104780 (0.0000) ss_Cl = 0.0016470 +/- 0.0004220 (0.0030) Set parameters: amp = 0.93 CN_O1 = 1 CN_O2 = 1 CN_Cl = 2 Correlations between variables: enot_Cl and delr_Cl --> 0.9479 enot_O2 and delr_O2 --> 0.9104 enot and enot_Cl --> 0.8766 enot and enot_O2 --> -0.8755 ss and delr_Cl --> 0.8737 delr_O2 and enot_Cl --> -0.8655 ss and enot_Cl --> 0.8469 enot_O2 and enot_Cl --> -0.8220 ss and delr_O2 --> -0.8025 enot and delr_Cl --> 0.7864 enot and delr_O2 --> -0.7825 delr_O2 and delr_Cl --> -0.7817 enot_O2 and ss_O2 --> 0.7535 delr_O2 and ss_O2 --> 0.7259 enot_O2 and delr_Cl --> -0.7080 ss and enot_O2 --> -0.6872 enot and ss --> 0.6795 delr_O2 and ss_Cl --> -0.6271 delr and ss_Cl --> -0.6217 ss_O2 and enot_Cl --> -0.6173 ss and ss_Cl --> 0.5740 ss_O2 and ss_Cl --> -0.5640 enot and ss_O2 --> -0.5314 enot_Cl and ss_Cl --> 0.5264 ss and ss_O2 --> -0.5084 enot_O2 and ss_Cl --> -0.4750 ss_O2 and delr_Cl --> -0.4747 delr_Cl and ss_Cl --> 0.4701 delr and ss_O2 --> 0.4134 enot and delr --> 0.3090 enot and ss_Cl --> 0.2693 All other correlations are below 0.25 ===== Data set >>SA 162deglitch-merge<< ======================================== file: C:\Program Files\Ifeffit\horae\stash\artemis.project.2\chi_data\SA_162deglitch-merge.chi title lines: Self absorption correction of 162deglitch-merge using method of Troger et al. + V K edge + Formula=H24.75 C8.25 O21.48 Si12.125 Cl4.7 V1.48 Merge in e space of: ** D:/200600603/Barnes-lab/EXAFS/NSLS/EXAFS/MYL-JULY-2006/all-VOCl3/162-Me2SiCl2+V5/162.001 ** D:/200600603/Barnes-lab/EXAFS/NSLS/EXAFS/MYL-JULY-2006/all-VOCl3/162-Me2SiCl2+V5/162.002 ** D:/200600603/Barnes-lab/EXAFS/NSLS/EXAFS/MYL-JULY-2006/all-VOCl3/162-Me2SiCl2+V5/162.003 k-range = 2.388 - 15.000 dk = 2.000 k-window = hanning k-weight = 2 R-range = 1.200 - 3.000 dR = 0.200 R-window = hanning fitting space = R background function = none phase correction = none R-factor for this data set = 0.01256 ===== Paths used to fit SA 162deglitch-merge FEFF1: Path 1: [O] .. feff = C:\Program Files\Ifeffit\horae\stash\artemis.project.2\data0.feff1\feff0001.dat id = reff= 1.6819, nlegs= 2, path= V<->O label = r = 1.840746 degen = 1.000000 s02 = 0.930000 e0 = 17.199906 dr = 0.158846 ss2 = -0.002272 3rd = 0.000000 4th = 0.000000 ei = 0.000000 FEFF1: Path 2: [O] .. feff = C:\Program Files\Ifeffit\horae\stash\artemis.project.2\data0.feff1\feff0002.dat id = reff= 1.8269, nlegs= 2, path= V<->O label = r = 1.605418 degen = 1.000000 s02 = 0.930000 e0 = -11.038494 dr = -0.221482 ss2 = 0.002756 3rd = 0.000000 4th = 0.000000 ei = 0.000000 FEFF1: Path 3: [Cl] .. feff = C:\Program Files\Ifeffit\horae\stash\artemis.project.2\data0.feff1\feff0003.dat id = reff= 2.1121, nlegs= 2, path= V<->Cl label = r = 2.100277 degen = 1.000000 s02 = 1.860000 e0 = -16.002670 dr = -0.011823 ss2 = 0.001647 3rd = 0.000000 4th = 0.000000 ei = 0.000000
Hi Rich, I know you posted this a while ago, so you may have gotten other answers, but I don't see them in my overflowing inbox. :) Years ago, I did some work with V2O3, and it was a very stubborn system to get a good fit on. Other people I knew who were working on the system have also had some trouble. This and other evidence led to some people publishing speculations on local distortions that get averaged out in XRD but show up in EXAFS. I also recall people talking about similar difficulties with other vanadium oxide systems. (Sorry; I don't have those references handy anymore, but searches should locate them). As far as the second issue you mention, with Ifeffit reversing the position of two atoms of the same species, it does happen some times. Why not? A V-O path is basically a V-O path to FEFF; it doesn't know that one's a single bond and one's a double bond. But since moving a path by more than about 0.1 Angstrom in Ifeffit starts to reduce the accuracy of the FEFF calculation, it's something you do want to try to prevent. One way to do that is with restraints; it shouldn't take much incentive for Ifeffit to refrain from switching the paths. --Scott Calvin Sarah Lawrence College At 05:02 PM 4/18/2007, you wrote:
Greetings!
I have inherited a vanadium EXAFS data set (due to a group member graduating - lucky dog!) that is giving me major fits. I am getting consistent numbers with all my fits which visually look fantastic, that is until I look at the numbers...one Debye-Waller factor is negative (a V-O path) and the Eo's are large, the V-Cl path is on the order of -20 eV, the V=O path is on the order of 17 eV, and the V-O path falling at -11 eV. ARe there any "tricks" outside of restraints or constraints that I can attempt to get more realistic values? (I understand that a large Eo can be realistic, but a negative Debye-Waller factor doesn't make sense.) I can restrain the V-O Debye-Waller factor and get a positive value, but then the V=O D-W factor is negative. If I restrain both D-W factors, the fit falls apart, suggesting something else is wrong that I just can't find.
Another issue I'm having involves something in Artemis that's confusing me. Sometimes after a fit, the Artemis Pallet shows the V=O feature as the one at 1.8 Angstroms and the V-O feature at 1.6 Angstroms, completely reversed to the FEFF model. I have seen this when I separated the chlorides as well (I attempted to model the Cl at different distances as reported by Deguns, et. al. (attached) due to the immediate environment around the V in our sample being similar to the one they report in scheme 1-(I), p5008). Attached is a text file that shows an Artemis Pallet output illustrating what I'm trying to describe for the V=O and V-O paths. The Artemis project that generated the output is also attached.
Scott, Thanks for the clues! The restraints seem to be working to get the DW factors positive. I'm still battling Ifeffit reversing the paths, but things are getting slowly better. Rich
Hi Rich,
I know you posted this a while ago, so you may have gotten other answers, but I don't see them in my overflowing inbox. :)
Years ago, I did some work with V2O3, and it was a very stubborn system to get a good fit on. Other people I knew who were working on the system have also had some trouble. This and other evidence led to some people publishing speculations on local distortions that get averaged out in XRD but show up in EXAFS. I also recall people talking about similar difficulties with other vanadium oxide systems. (Sorry; I don't have those references handy anymore, but searches should locate them).
As far as the second issue you mention, with Ifeffit reversing the position of two atoms of the same species, it does happen some times. Why not? A V-O path is basically a V-O path to FEFF; it doesn't know that one's a single bond and one's a double bond. But since moving a path by more than about 0.1 Angstrom in Ifeffit starts to reduce the accuracy of the FEFF calculation, it's something you do want to try to prevent. One way to do that is with restraints; it shouldn't take much incentive for Ifeffit to refrain from switching the paths.
--Scott Calvin Sarah Lawrence College
At 05:02 PM 4/18/2007, you wrote:
Greetings!
I have inherited a vanadium EXAFS data set (due to a group member graduating - lucky dog!) that is giving me major fits. I am getting consistent numbers with all my fits which visually look fantastic, that is until I look at the numbers...one Debye-Waller factor is negative (a V-O path) and the Eo's are large, the V-Cl path is on the order of -20 eV, the V=O path is on the order of 17 eV, and the V-O path falling at -11 eV. ARe there any "tricks" outside of restraints or constraints that I can attempt to get more realistic values? (I understand that a large Eo can be realistic, but a negative Debye-Waller factor doesn't make sense.) I can restrain the V-O Debye-Waller factor and get a positive value, but then the V=O D-W factor is negative. If I restrain both D-W factors, the fit falls apart, suggesting something else is wrong that I just can't find.
Another issue I'm having involves something in Artemis that's confusing me. Sometimes after a fit, the Artemis Pallet shows the V=O feature as the one at 1.8 Angstroms and the V-O feature at 1.6 Angstroms, completely reversed to the FEFF model. I have seen this when I separated the chlorides as well (I attempted to model the Cl at different distances as reported by Deguns, et. al. (attached) due to the immediate environment around the V in our sample being similar to the one they report in scheme 1-(I), p5008). Attached is a text file that shows an Artemis Pallet output illustrating what I'm trying to describe for the V=O and V-O paths. The Artemis project that generated the output is also attached.
_______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
My observation (not rigorously tested though): the longer it takes to get a good fit, the more suspicious are the results! Anatoly -----Original Message----- From: ifeffit-bounces@millenia.cars.aps.anl.gov [mailto:ifeffit-bounces@millenia.cars.aps.anl.gov]On Behalf Of Richard Mayes Sent: Wednesday, May 02, 2007 8:56 AM To: XAFS Analysis using Ifeffit Subject: Re: [Ifeffit] large Eo's and neg. D-W factors Scott, Thanks for the clues! The restraints seem to be working to get the DW factors positive. I'm still battling Ifeffit reversing the paths, but things are getting slowly better. Rich
Hi Rich,
I know you posted this a while ago, so you may have gotten other answers, but I don't see them in my overflowing inbox. :)
Years ago, I did some work with V2O3, and it was a very stubborn system to get a good fit on. Other people I knew who were working on the system have also had some trouble. This and other evidence led to some people publishing speculations on local distortions that get averaged out in XRD but show up in EXAFS. I also recall people talking about similar difficulties with other vanadium oxide systems. (Sorry; I don't have those references handy anymore, but searches should locate them).
As far as the second issue you mention, with Ifeffit reversing the position of two atoms of the same species, it does happen some times. Why not? A V-O path is basically a V-O path to FEFF; it doesn't know that one's a single bond and one's a double bond. But since moving a path by more than about 0.1 Angstrom in Ifeffit starts to reduce the accuracy of the FEFF calculation, it's something you do want to try to prevent. One way to do that is with restraints; it shouldn't take much incentive for Ifeffit to refrain from switching the paths.
--Scott Calvin Sarah Lawrence College
At 05:02 PM 4/18/2007, you wrote:
Greetings!
I have inherited a vanadium EXAFS data set (due to a group member graduating - lucky dog!) that is giving me major fits. I am getting consistent numbers with all my fits which visually look fantastic, that is until I look at the numbers...one Debye-Waller factor is negative (a V-O path) and the Eo's are large, the V-Cl path is on the order of -20 eV, the V=O path is on the order of 17 eV, and the V-O path falling at -11 eV. ARe there any "tricks" outside of restraints or constraints that I can attempt to get more realistic values? (I understand that a large Eo can be realistic, but a negative Debye-Waller factor doesn't make sense.) I can restrain the V-O Debye-Waller factor and get a positive value, but then the V=O D-W factor is negative. If I restrain both D-W factors, the fit falls apart, suggesting something else is wrong that I just can't find.
Another issue I'm having involves something in Artemis that's confusing me. Sometimes after a fit, the Artemis Pallet shows the V=O feature as the one at 1.8 Angstroms and the V-O feature at 1.6 Angstroms, completely reversed to the FEFF model. I have seen this when I separated the chlorides as well (I attempted to model the Cl at different distances as reported by Deguns, et. al. (attached) due to the immediate environment around the V in our sample being similar to the one they report in scheme 1-(I), p5008). Attached is a text file that shows an Artemis Pallet output illustrating what I'm trying to describe for the V=O and V-O paths. The Artemis project that generated the output is also attached.
_______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
_______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
Hi Rich, Oh--I think I should have been more specific. It sounds like you're restraining the sigma2's. In my experience, that is not as effective in the cases of switching paths as restraining the delr's. After all, the sigma2's are just a symptom; the delr's are the direct measure of switching. As for Anatoly's observation, I'd qualify it. If it's a matter of trying to pound a square peg into a round hole, then yeah, that's dubious. I often have found, though, that I get lousy fit after lousy fit for a long time. Then I make some key change to how I'm =physically= modelling the system...allowing vacancies, or putting in a minority phase, or changing the morphology, or allowing for local distortion, or whatever, and suddenly the fits get much much better. I often have pretty high confidence in the results when that happens. It suggests that in that system I can't get a good fit with the wrong model just by tinkering. In the other extreme, if I have the kind of combination of data and model that seems to give a "good" fit no matter what I do, but from one fit to the next the parameters jump all over the place, then I have low confidence in the results. In other words, I want systems that generate lousy fits unless I get the structure right. :) --Scott Calvin Sarah Lawrence College At 08:55 AM 5/2/2007, you wrote:
Scott,
Thanks for the clues! The restraints seem to be working to get the DW factors positive. I'm still battling Ifeffit reversing the paths, but things are getting slowly better.
Rich
Hi Rich,
I know you posted this a while ago, so you may have gotten other answers, but I don't see them in my overflowing inbox. :)
Years ago, I did some work with V2O3, and it was a very stubborn system to get a good fit on. Other people I knew who were working on the system have also had some trouble. This and other evidence led to some people publishing speculations on local distortions that get averaged out in XRD but show up in EXAFS. I also recall people talking about similar difficulties with other vanadium oxide systems. (Sorry; I don't have those references handy anymore, but searches should locate them).
As far as the second issue you mention, with Ifeffit reversing the position of two atoms of the same species, it does happen some times. Why not? A V-O path is basically a V-O path to FEFF; it doesn't know that one's a single bond and one's a double bond. But since moving a path by more than about 0.1 Angstrom in Ifeffit starts to reduce the accuracy of the FEFF calculation, it's something you do want to try to prevent. One way to do that is with restraints; it shouldn't take much incentive for Ifeffit to refrain from switching the paths.
--Scott Calvin Sarah Lawrence College
At 05:02 PM 4/18/2007, you wrote:
Greetings!
I have inherited a vanadium EXAFS data set (due to a group member graduating - lucky dog!) that is giving me major fits. I am getting consistent numbers with all my fits which visually look fantastic, that is until I look at the numbers...one Debye-Waller factor is negative (a V-O path) and the Eo's are large, the V-Cl path is on the order of -20 eV, the V=O path is on the order of 17 eV, and the V-O path falling at -11 eV. ARe there any "tricks" outside of restraints or constraints that I can attempt to get more realistic values? (I understand that a large Eo can be realistic, but a negative Debye-Waller factor doesn't make sense.) I can restrain the V-O Debye-Waller factor and get a positive value, but then the V=O D-W factor is negative. If I restrain both D-W factors, the fit falls apart, suggesting something else is wrong that I just can't find.
Another issue I'm having involves something in Artemis that's confusing me. Sometimes after a fit, the Artemis Pallet shows the V=O feature as the one at 1.8 Angstroms and the V-O feature at 1.6 Angstroms, completely reversed to the FEFF model. I have seen this when I separated the chlorides as well (I attempted to model the Cl at different distances as reported by Deguns, et. al. (attached) due to the immediate environment around the V in our sample being similar to the one they report in scheme 1-(I), p5008). Attached is a text file that shows an Artemis Pallet output illustrating what I'm trying to describe for the V=O and V-O paths. The Artemis project that generated the output is also attached.
_______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
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Scott, I think I understand now. By restraining the negative Debye-Waller factor, I may have been treating the symptom instead of the cause. I'll go back and check my model. Also, should I be worried if my Debye-Waller factors get small (0.0005-0.001) if I optimize my model in FEFF to a point that my delr's are on the order of 0.005-0.01 Angstroms? This has been a concern of ours since we started doing EXAFS, especially since all of our measurements are at room temp. We haven't seen this as much with our vanadium on silica samples, but it seems to be true with all of our titanosilicate samples Rich Scott Calvin wrote:
Hi Rich,
Oh--I think I should have been more specific. It sounds like you're restraining the sigma2's. In my experience, that is not as effective in the cases of switching paths as restraining the delr's. After all, the sigma2's are just a symptom; the delr's are the direct measure of switching.
As for Anatoly's observation, I'd qualify it. If it's a matter of trying to pound a square peg into a round hole, then yeah, that's dubious. I often have found, though, that I get lousy fit after lousy fit for a long time. Then I make some key change to how I'm =physically= modelling the system...allowing vacancies, or putting in a minority phase, or changing the morphology, or allowing for local distortion, or whatever, and suddenly the fits get much much better. I often have pretty high confidence in the results when that happens. It suggests that in that system I can't get a good fit with the wrong model just by tinkering. In the other extreme, if I have the kind of combination of data and model that seems to give a "good" fit no matter what I do, but from one fit to the next the parameters jump all over the place, then I have low confidence in the results. In other words, I want systems that generate lousy fits unless I get the structure right. :)
--Scott Calvin Sarah Lawrence College
At 08:55 AM 5/2/2007, you wrote:
Scott,
Thanks for the clues! The restraints seem to be working to get the DW factors positive. I'm still battling Ifeffit reversing the paths, but things are getting slowly better.
Rich
Hi Rich,
I know you posted this a while ago, so you may have gotten other answers, but I don't see them in my overflowing inbox. :)
Years ago, I did some work with V2O3, and it was a very stubborn system to get a good fit on. Other people I knew who were working on the system have also had some trouble. This and other evidence led to some people publishing speculations on local distortions that get averaged out in XRD but show up in EXAFS. I also recall people talking about similar difficulties with other vanadium oxide systems. (Sorry; I don't have those references handy anymore, but searches should locate them).
As far as the second issue you mention, with Ifeffit reversing the position of two atoms of the same species, it does happen some times. Why not? A V-O path is basically a V-O path to FEFF; it doesn't know that one's a single bond and one's a double bond. But since moving a path by more than about 0.1 Angstrom in Ifeffit starts to reduce the accuracy of the FEFF calculation, it's something you do want to try to prevent. One way to do that is with restraints; it shouldn't take much incentive for Ifeffit to refrain from switching the paths.
--Scott Calvin Sarah Lawrence College
At 05:02 PM 4/18/2007, you wrote:
Greetings!
I have inherited a vanadium EXAFS data set (due to a group member graduating - lucky dog!) that is giving me major fits. I am getting consistent numbers with all my fits which visually look fantastic, that is until I look at the numbers...one Debye-Waller factor is negative (a V-O path) and the Eo's are large, the V-Cl path is on the order of -20 eV, the V=O path is on the order of 17 eV, and the V-O path falling at -11 eV. ARe there any "tricks" outside of restraints or constraints that I can attempt to get more realistic values? (I understand that a large Eo can be realistic, but a negative Debye-Waller factor doesn't make sense.) I can restrain the V-O Debye-Waller factor and get a positive value, but then the V=O D-W factor is negative. If I restrain both D-W factors, the fit falls apart, suggesting something else is wrong that I just can't find.
Another issue I'm having involves something in Artemis that's confusing me. Sometimes after a fit, the Artemis Pallet shows the V=O feature as the one at 1.8 Angstroms and the V-O feature at 1.6 Angstroms, completely reversed to the FEFF model. I have seen this when I separated the chlorides as well (I attempted to model the Cl at different distances as reported by Deguns, et. al. (attached) due to the immediate environment around the V in our sample being similar to the one they report in scheme 1-(I), p5008). Attached is a text file that shows an Artemis Pallet output illustrating what I'm trying to describe for the V=O and V-O paths. The Artemis project that generated the output is also attached.
_______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
_______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
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Hi Rich, It depends on the information you want out. Here's where it's good to think about correlated effects. Sigma2's affect primarily the amplitude. They therefore correlate highly with coordination number, S02, normalization, sample quality (e.g. variable thickness in transmission; self-absorption in fluorescence), beamline effects (e.g. harmonics), and the like. Other variables are primarily a question of phase: E0, delr, and the third cumulant, to name some of the more important ones. Of course, some factors, such as the elemental identity of the scattering atom or the fraction of various phases that are present, affect both amplitude and phase. If you're interested in knowing about the phase variables, then the amplitude variables are less crucial. A slightly wonky value can come from something else being slightly wonky; e.g. normalization. That's not ideal, and should make you nervous enough to poke at it a bit (for example, go back and look carefully at the normalization in Athena). But it's not nearly as serious as if you are interested in an amplitude variable. For example, if you're trying to fit coordination numbers, then a weird sigma2 is a big big red flag. Finally, this is the kind of place where analyzing a standard of known structure is immensely helpful. Likewise, a temperature series can be very helpful for sorting out some of the correlated variables. Hope that helps. --Scott Calvin Sarah Lawrence College At 10:52 AM 5/2/2007, you wrote:
Also, should I be worried if my Debye-Waller factors get small (0.0005-0.001) if I optimize my model in FEFF to a point that my delr's are on the order of 0.005-0.01 Angstroms? This has been a concern of ours since we started doing EXAFS, especially since all of our measurements are at room temp. We haven't seen this as much with our vanadium on silica samples, but it seems to be true with all of our titanosilicate samples
participants (4)
-
Anatoly Frenkel -
Richard Mayes -
Scott Calvin -
Scott Calvin