Hi Scott, look also at H and O, but for me and for this fit important are only W-C and W-C-N bondings. This sample is an reference sample for other cyano-brigded networks. So you suggest to focuse on K ions? how can it help with first 2 peaks? K is at ~5A. I have analysed in larger R space only to see how the spectrum behave. contribution from K, O etc. at k highers than 5A is for me too low to analyse it resonable for such compound. I have attached in the previus post the last version of results. Anyway, enots for C and N do not change if I am enlarging R region (when I am including next paths, also for K). about material I am quite sure ;) and crystal structure is from literature in the attachment you will find bmp file of the fit: data, fit, bkg and K path. fitting ranges k(3-15) R(1.7-6) dk 2 dr 0.5, phase correction - first C cheers darek
-----Original Message----- From: ifeffit-bounces@millenia.cars.aps.anl.gov [mailto:ifeffit-bounces@millenia.cars.aps.anl.gov] On Behalf Of Scott Calvin Sent: Friday, June 19, 2009 1:46 PM To: XAFS Analysis using Ifeffit Subject: Re: [Ifeffit] problem with E0 (enot) parameters
Hi Darek,
You've got a false fit. The E0's aren't the biggest problem; look at the delr for potassium! Your fit is scrambling all the paths in non- physical ways.
Your initial description of the system suggests that you have a decent guess as to the structure to start with. What happens when you run a fit with very few free parameters? (Perhaps none, or perhaps just floating an overall S02, E0, and maybe a couple of sigma2's.) Does it look qualitatively right, with peaks where there should be peaks? If so, then you probably need a tighter set of constraints. If not, then the material is not what you think it is.
--Scott Calvin Sarah Lawrence College
On Jun 19, 2009, at 7:30 AM, Zajac, Dariusz A. wrote:
Hi Calvin, thanks for the email. I have tried to find something on mailing list about E0 but it seems that my "searching words" were not correct. I found only few posts but non of them explained (or followed) the problem with large enot. enot parameters are closed to eachother e.g. enot_C = 12.597(+-0.654) and enot_N=12.407(+-1.776); correlations e.g. enot_N and delr_N=0.744, enot_C and delr_C=0.605 enot_C and enot_N=-0.313 more detail you can find in the attachment or below. I have found that the value of the first background variable is large (-3437(+-23034)) when I constrain both enot's parameters I do not see huge changes in parameters, chi^2 enot, amp, delr and ssh are the same in the range of uncertainties. I agree with you that program can shift not the correct parameter, but why every time I change parameters (I shift parameters from the local minimum) their come back?
cheers darek
Independent points = 45.279296875 Number of variables = 30.000000000 Chi-square = 219223.767 Reduced Chi-square = 14347.765383235 R-factor = 0.022707172 Measurement uncertainty (k) = 0.000102780 Measurement uncertainty (R) = 0.000306293 Number of data sets = 1.000000000
Guess parameters +/- uncertainties (initial guess): amp = 0.8496050 +/- 0.0767160 (guessed as 0.849812 (0.095158)) enot_C = 12.5967170 +/- 0.6539780 (guessed as 12.601228 (0.744286)) delr_C = -0.0055260 +/- 0.0068920 (guessed as -0.005265 (0.007572)) ss_C = 0.0016740 +/- 0.0008460 (guessed as 0.001676 (0.000991)) enot_N = 12.4065290 +/- 1.7757010 (guessed as 12.895967 (2.018563)) delr_N = 0.0358140 +/- 0.0193390 (guessed as 0.042607 (0.029913)) ss_N = 0.0068930 +/- 0.0016280 (guessed as 0.008196 (0.002599)) enot_K = 0.0064050 +/- 9.7412920 (guessed as -4.066616 (13.931541)) delr_K = 0.9265430 +/- 0.1815320 (guessed as -0.018996 (0.154984)) ss_K = 0.0074030 +/- 0.0124260 (guessed as 0.011457 (0.010167)) enot_O = -8.4988040 +/- 13.7627610 (guessed as 0.906319 (10.059312)) delr_O = -0.3610320 +/- 0.0975640 (guessed as -0.139554 (0.069016)) ss_O = 0.0010060 +/- 0.0050660 (guessed as 0.001140 (0.004395))
Def parameters (using "FEFF0: Path 1: [C5_1]"): enot_CN = 12.5016230 delr_CN = 0.0151440 ss_CN = 0.0042840 enot_CNC = 12.5333210 delr_CNC = 0.0082540 ss_CNC = 0.0034140 enot_NCN = 12.4699250 delr_NCN = 0.0220340 ss_NCN = 0.0051540 enot_KN = 6.2064670 delr_KN = 0.4811790 ss_KN = 0.0071480 enot_KC = 6.3015610 delr_KC = 0.4605080 ss_KC = 0.0045380 enot_KNC = 8.3365500 delr_KNC = 0.3189440 ss_KNC = 0.0053230
Set parameters: enot_H = -0.920939 (0.000000) delr_H = 0.103335 (0.000000) ss_H = 0.00749823 (0.000000)
Background parameters +/- uncertainties: bkg01_01 = -3437.6705554 +/- 23034.7299514 bkg01_02 = -0.0609379 +/- 1.8005458 bkg01_03 = 0.1948870 +/- 0.1595573 bkg01_04 = -0.0398830 +/- 0.0358870 bkg01_05 = -0.0025572 +/- 0.0147361 bkg01_06 = 0.0067564 +/- 0.0081250 bkg01_07 = -0.0031386 +/- 0.0052991 bkg01_08 = 0.0006703 +/- 0.0037900 bkg01_09 = -0.0000756 +/- 0.0028462 bkg01_10 = 0.0003428 +/- 0.0022025 bkg01_11 = -0.0006552 +/- 0.0017628 bkg01_12 = 0.0006924 +/- 0.0015077 bkg01_13 = -0.0004210 +/- 0.0015140 bkg01_14 = -0.0002224 +/- 0.0022632 bkg01_15 = 0.0026167 +/- 0.0075534 bkg01_16 = -0.0207863 +/- 0.0762094 bkg01_17 = 48.5761922 +/- 4197.5368888
Correlations between variables: enot_K and delr_K --> 0.8386 enot_O and delr_O --> 0.8120 enot_N and delr_N --> 0.7440 amp and ss_C --> 0.7232 enot_C and delr_C --> 0.6048 amp and enot_N --> 0.5755 enot_C and bkg01_02 --> -0.4957 amp and bkg01_05 --> 0.4817 amp and bkg01_04 --> -0.4376 enot_C and bkg01_03 --> 0.4175 enot_N and enot_O --> 0.3976 ss_C and enot_N --> 0.3902 amp and bkg01_06 --> -0.3779 amp and ss_N --> 0.3767 amp and enot_C --> -0.3652 ss_C and delr_N --> 0.3422 ss_N and bkg01_04 --> -0.3330 amp and delr_N --> 0.3325 ss_C and bkg01_15 --> -0.3311 ss_N and bkg01_05 --> 0.3172 enot_C and enot_N --> -0.3133 enot_N and bkg01_02 --> 0.2957 enot_N and delr_O --> 0.2918 delr_C and ss_N --> -0.2832 delr_N and enot_O --> 0.2804 ss_C and bkg01_16 --> 0.2690 ss_C and bkg01_05 --> 0.2663 delr_C and delr_N --> -0.2572 ss_C and bkg01_14 --> 0.2569 amp and enot_O --> 0.2560 ss_C and bkg01_04 --> -0.2528 All other correlations are below 0.25
-----Original Message----- From: ifeffit-bounces@millenia.cars.aps.anl.gov [mailto:ifeffit-bounces@millenia.cars.aps.anl.gov] On Behalf Of Scott Calvin Sent: Friday, June 19, 2009 12:23 PM To: XAFS Analysis using Ifeffit Subject: Re: [Ifeffit] problem with E0 (enot) parameters
Hi Zajac,
What happens if you constrain all E0's to be the same? In the fit where they come out large, what are the uncertainties in the E0's? What are their correlations with other fitted parameters? There has been some debate in this list on the past as to how useful it is to allow for different E0's for different paths. It may be
Background parameters "bkg01_XX" belong to data set RP314a K4W(CN)8x2H2O W:L3 that Artemis
is shifting the E0's for those paths in lieu of some other correlated parameter.
--Scott Calvin Sarah Lawrence College
On Jun 19, 2009, at 5:33 AM, Zajac, Dariusz A. wrote:
Hi all, can anybody help me and send some link about problems with enot in Artemis? in google, tutorials I couldn't find any help. Of course are few posts about delr or ss parameters, but enot is somehow omited (or I can not find it...)
the problem is with fiting K4W(CN)8*2H2O at W:L3 edge. fit and others parameters looks ok, except enot for C and N, where both are around 12 and don't want to fit to other values... thanks darek
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