[Ifeffit] problem with E0 (enot) parameters
Zajac, Dariusz A.
dariusz.zajac at desy.de
Fri Jun 19 07:28:20 CDT 2009
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 at millenia.cars.aps.anl.gov
>[mailto:ifeffit-bounces at 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
>>
>> Background parameters "bkg01_XX" belong to data set RP314a
>> K4W(CN)8x2H2O
>> W:L3
>>> -----Original Message-----
>>> From: ifeffit-bounces at millenia.cars.aps.anl.gov
>>> [mailto:ifeffit-bounces at 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
>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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