[Ifeffit] Fitting Commercial Molybdenum Disulfide

[Kelly, Shelly D.]

Hi Dan,

Take a look at the fit in q-space with the model below.  I suspect that
you have left out important Multiple scattering paths that would cause a
miss-fit to the data at low k values.  To test for this, change the fit
range to something like 4.0 1/Anstroms for k-min value, and try again.

Shelly

> -----Original Message-----
> From: dmc at pdx.edu [mailto:dmc at pdx.edu] 
> Sent: Friday, October 29, 2004 11:03 AM
> To: XAFS Analysis using Ifeffit
> Subject: RE: [Ifeffit] Fitting Commercial Molybdenum Disulfide
> 
> 
> Hi Shelly,
> 
>      I seperated the delr's with different alpha terms, but 
> Mike seems to think 
> that this is assuming isotropic expansion that isn't there.  
> Also, the reduced 
> chi-square has gone up 150 or so.   
> 
> delr#  define:  alpha# * reff
> 
> 
>                   Thanks for the help, Dan 
> 
> 
> Results with 1 eO and differing delr's:
> 
> Independent points          =      14.312500000
> Number of variables         =       7.000000000
> Chi-square                  =    6186.771083042
> Reduced Chi-square          =     846.054165202
> R-factor                    =       0.031090393
> Measurement uncertainty (k) =       0.000181935
> Measurement uncertainty (R) =       0.004860095
> Number of data sets         =       1.000000000
> 
> 
> Guess parameters +/- uncertainties  (initial guess):
>   ss              =     0.0042720   +/-      0.0006590    
> (guessed as 0.004636 
> (0.000411))
>   e0              =     1.3293700   +/-      1.4673640    
> (guessed as 1.765958 
> (1.154388))
>   alpha           =    -0.0001750   +/-      0.0040010    
> (guessed as 0.001090 
> (0.002843))
>   ss2             =     0.0043180   +/-      0.0007370    (0.0000)
>   ss3             =     0.0072300   +/-      0.0164390    (0.0000)
>   alpha2          =     0.0076940   +/-      0.0027880    (0.0000)
>   alpha3          =    -0.0512670   +/-      0.0232140    (0.0000)
> 
> Def parameters:
>   delr_1          =    -0.0006930
>   delr_2          =     0.0305320
>   delr_3          =    -0.2034430
> 
> Set parameters:
>   amp             =  0.7
> 
> 
> Correlations between variables:
>           e0 and alpha      -->  0.8441
>          ss3 and alpha2     -->  0.7651
>          ss2 and alpha2     --> -0.6441
>           e0 and alpha2     -->  0.5682
>          ss2 and ss3        -->  0.4871
>        alpha and alpha2     -->  0.4785
>          ss3 and alpha3     -->  0.3825
>           e0 and alpha3     --> -0.2743
> All other correlations are below 0.25
> 
> 
> 
> 
> 
> Original (2 e0s):  
> 
> 
> Independent points          =      14.312500000
> Number of variables         =       6.000000000
> Chi-square                  =    5778.957783654
> Reduced Chi-square          =     695.212966455
> R-factor                    =       0.029041008
> Measurement uncertainty (k) =       0.000181935
> Measurement uncertainty (R) =       0.004860095
> Number of data sets         =       1.000000000
> 
> 
> Guess parameters +/- uncertainties  (initial guess):
>   e0_1            =    -4.0347670   +/-      2.9998980    
> (guessed as -4.072009 
> (1.919404))
>   ss              =     0.0042860   +/-      0.0005990    
> (guessed as 0.004636 
> (0.000411))
>   e0              =     1.6770760   +/-      1.3230290    
> (guessed as 1.765958 
> (1.154388))
>   alpha           =     0.0009180   +/-      0.0034050    
> (guessed as 0.001090 
> (0.002843))
>   ss2             =     0.0048160   +/-      0.0006910    (0.0000)
>   ss3             =     0.0225310   +/-      0.0657250    (0.0000)
> 
> Def parameters:
>   delr_1          =     0.0036440
> 
> Set parameters:
>   amp             =  0.7
> 
> 
> Correlations between variables:
>         e0_1 and alpha      -->  0.8542
>           e0 and alpha      -->  0.8470
>         e0_1 and e0         -->  0.7407
>         e0_1 and ss3        -->  0.7060
>        alpha and ss3        -->  0.4715
>          ss2 and ss3        --> -0.4214
>         e0_1 and ss2        --> -0.3892
>           e0 and ss3        -->  0.3772
>        alpha and ss2        --> -0.2680
> All other correlations are below 0.25
> 
> 
> 
> 
> 
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