[Ifeffit] configurational average
Matt Newville
newville at cars.uchicago.edu
Tue Mar 16 15:10:50 CST 2004
Dear Prof Matsuura,
Feff8 does claim to allow configurational averages for EXAFS.
Unfortunately, the results with CFAVERAGE are clearly wrong even in
simple test cases. At the most basic level, in order to describe a
configurational averaged environment, fractional degeneracies would
be necessary. The feffnnn.dat files *never* report fractional
degeneracy, even when using CFAVERAGE. This should immediately make
you very suspicious that something is not right.
I recommend not using the CFAVERAGE card, and instead making
separate feff runs for each candidate central atom, and then
averaging these sets of calculations, weighted by the fraction for
each candidate central atom. It's unfortunate that the tools for
modeling EXAFS of disordered crystals are so crude... there's
probably a lot of room for improvement in this area!
Hope that helps,
--Matt
On Tue, 16 Mar 2004, Makoto Matsuura wrote:
> My question is how the path files (feffxxx.dat) are defined when
> "configurational average" is used in feff calculation.
> And how we apply path data avaraged configurationally to the fitting
> calculation.
> For example in case of CaCu5 structure two Cu sites are there, i.e. 3g and
> 2c site.
> If we use control card of "CFAVERAGE" in feff calculation with setting Cu 3g
> as a core. Then configurational average will be done over the 2c sites.
> The below shows the two log files of feff8 ( list.log ) in the case of the
> configurationally averaged (core Cu 3g site) and without configurationally
> averaged.
> I calculate Fourier transform (RSF) using each path (feffxxxx.dat) deduced
> by feff calculation applying configurationally averaged and compared with
> that of the total one. I fail to coincide sum of RSF's for each path with
> the total RSF.
> I like to know the reason of it.
>
> Next question is how we use the paths (feffxxxx.dat) in the feffit
> calculation when we use "configurational average" in feff calculation.
> Can we use the feffxxxx.dat files as it is for the feffit?
>
> list of list.log when configurationally average card is used.
> ////////////////////////////////////////////////////////////////////////////
> ///////////////////////////////////
> Cu K-edge for Cu 3g of CaCu5:output for feff8 absorber Feff 8.10
> Cu configurational avaraged with Cu2c site
> DEBYE temp =300K at 20K
> Abs Z=28 Rmt= 1.347 Rnm= 1.394 K shell
> Pot 1 Z=28 Rmt= 1.354 Rnm= 1.403
> Pot 2 Z=57 Rmt= 1.773 Rnm= 1.830
> Gam_ch=1.576E+00 H-L exch
> Mu=-1.168E+01 kf=1.918E+00 Vint=-2.026E+01 Rs_int= 1.891
> -----------------------------------------------------------------------
> pathindex sig2 amp ratio deg nlegs r effective
> 1 0.00000 100.000 2.000 2 2.4634
> 2 0.00000 93.844 2.000 2 3.2025
> 3 0.00000 16.979 1.000 2 3.9873
> 4 0.00000 13.047 8.000 3 4.2800
> 5 0.00000 55.603 4.000 2 4.3163
> 6 0.00000 44.329 4.000 2 4.7095
> 7 0.00000 36.814 2.000 2 4.7769
> 8 0.00000 19.574 8.000 3 4.8182
> 9 0.00000 8.950 8.000 3 4.8369
> 10 0.00000 4.441 2.000 4 4.9269
> 11 0.00000 3.423 4.000 4 4.9268
> 12 0.00000 8.603 4.000 3 5.0671
> 13 0.00000 13.297 8.000 3 5.2064
> 14 0.00000 11.402 8.000 3 5.5573
> 15 0.00000 27.903 4.000 2 5.5851
> 16 0.00000 3.001 8.000 4 5.6659
> 17 0.00000 31.325 8.000 3 5.8408
> 18 0.00000 23.977 4.000 2 5.8943
> 19 0.00000 8.327 4.000 4 6.0965
> 20 0.00000 25.802 8.000 3 6.1496
>
> list of list.log without using configurational average
> ////////////////////////////////////////////////////////////////////////////
> //////////
> Cu K-edge for Cu 3g of CaCu5:output for feff8 absorber Feff 8.10
> Cu No configurational avaraged
> DEBYE temp =180K at 20K
> Abs Z=28 Rmt= 1.347 Rnm= 1.394 K shell
> Pot 1 Z=28 Rmt= 1.354 Rnm= 1.403
> Pot 2 Z=57 Rmt= 1.773 Rnm= 1.830
> Gam_ch=1.576E+00 H-L exch
> Mu=-1.168E+01 kf=1.918E+00 Vint=-2.026E+01 Rs_int= 1.891
> -----------------------------------------------------------------------
> pathindex sig2 amp ratio deg nlegs r effective
> 1 0.00000 100.000 4.000 2 2.4634
> 2 0.00000 96.591 4.000 2 2.5063
> 3 0.00000 93.844 4.000 2 3.2025
> 4 0.00000 14.579 16.000 3 3.7165
> 5 0.00000 16.979 2.000 2 3.9873
> 6 0.00000 13.047 16.000 3 4.2800
> 7 0.00000 55.603 8.000 2 4.3163
> 8 0.00000 27.399 4.000 2 4.3410
> 9 0.00000 8.758 16.000 3 4.4556
> 10 0.00000 12.606 16.000 3 4.6430
> 11 0.00000 12.963 16.000 3 4.6430
> 12 0.00000 6.132 8.000 3 4.6767
> 13 0.00000 44.329 8.000 2 4.7095
> 14 0.00000 36.814 4.000 2 4.7769
> 15 0.00000 19.574 16.000 3 4.8182
> 16 0.00000 8.950 16.000 3 4.8369
> 17 0.00000 10.192 4.000 3 4.9269
> 18 0.00000 9.147 4.000 4 4.9269
> 19 0.00000 4.441 4.000 4 4.9269
> 20 0.00000 3.423 8.000 4 4.9268
> ******************************************
>
> Miyagi National College of Technology
>
> Prof. Makoto Matsuura
>
> email: matsuura at miyagi-ct.ac.jp
> TEL&FAX 022-381-0270
>
> ******************************************
>
>
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