[Ifeffit] problem of overestimated E0 (Edge-energy)
Kropf, Arthur Jeremy
kropf at anl.gov
Thu Jan 12 16:05:25 CST 2012
I think we'll need more information to help out: at a minimum, the
feff.inp file. Also, are you fitting just the nearest neighbor
scattering path?
To begin to answer your question, while it is often the case that Eo
falls below the white line peak, this is not categorically true. A
relevant example might be PtO2.
Jeremy
Chemical Sciences and Engineering Division
Argonne National Laboratory
Argonne, IL 60439
Ph: 630.252.9398
Fx: 630.252.9917
Email: kropf at anl.gov
From: ifeffit-bounces at millenia.cars.aps.anl.gov
[mailto:ifeffit-bounces at millenia.cars.aps.anl.gov] On Behalf Of
JeongEunSuk
Sent: Thursday, January 12, 2012 3:47 PM
To: ifeffit
Subject: [Ifeffit] problem of overestimated E0 (Edge-energy)
________________________________
Hello all
I want to understand EO(edge-energy), precisely. (In Artemis, EO is
writed as Enor)
Generally, EO is energy when electrons start to go out from core atom in
XAFS.
As you know, the experiments show that to find EO is not easy in XAFS.
To remove background, sometimes I chose EO, the value of the maximum
derivative in Athena.
and when fitting, the E0 is correted by theoritical FEFF.
This is my question.
The attached file is the figure of Pt foil(Pt L3 edge measurement).
I think edge-enegy has to be in range between A and C because electrons
start to move to continum state in that range.
However, fitted E0 is shifted to C (about 11573eV). and then when
removing background I chose E0=11563eV(This is Pt L3 edge).
Fitted E0 is overestimated value, compared with whit line(B).
That means the calculated EO obtained from FEFF8.0 (using auto-self
consistency field potential) is larg! er than that of experiment.
Do I need to change SCF potential in FEFF8.0?
------------------------------------------------------------------------
----------------------------------------------------
This is fitting parameters and results(in my case, I used Linux version)
To remove background
k -range = 2.5 ~ 15, EO=11563eV, Rbkg=1.3, kweight =1
To fit data
k -range = 3.0~13.5, R -range =2.3~13.5
1. fitting parameters
set macc = 0.0
set so2 = 0.89 // reduction factor
guess ePt = 0.0 // energy shift
set npt1=1.0 // the number of Pt (1.0 means 12 Pt
atoms around core Pt)
gu! ess dpt1 = 0.0042 // effective bonding length
guess sigpt1=0.005100 //Debye waller factor
2. fitting results
fit results, goodness of fit, and error analysis:
independent points in data = 8.152
number of variables in fit = 3
degrees of freedom in fit = 5.152
r-factor of fit = 0.002700
chi-square = 1267.097168
! ; reduced chi-square &nb! sp; = 245.926361
feffit found the following values for the variables:
variable best fit value uncertainty initial guess
ept = 10.758198 0.860494 4.000000
dpt1 = 0.006462 0.002930 0.004200
sigpt1 = &nbs! p; 0.005114 0.000098
0.005100
correlation between variables
variable #1 variable #2 correlation
ept dpt1 0.926524
all other correlations are less than 0.25000
------------------------------------------------------------------------
---------------------
Because the correlation between E0 and effective bonding length is big,
I checked the fit as set bonding and the rest of parameters is
variables, and then the result is not changed. That means EO still is
big.
&! nbsp;
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