[Ifeffit] MoS2 fit

dmc at pdx.edu dmc at pdx.edu
Tue Aug 17 14:02:53 CDT 2004

Hi Shelly,

     Thanks for the suggestions, here's what happened.

> Backfourier transform:    
> Do they miss more at low q or high q?  Missing at low q/k would suggest
> separate dE values while missing at high q/k would suggest separate delr
> values.

       It looks to me like they are missing at low q/k.  I will try to attach a

> Would your model be better described by using an overall
> expansion/contraction term rather than one delr value?
> Using one delr means that all the paths move by -0.01 angstroms.  Using
> one expansion term would allow all paths to contract by 0.1%  which
> might be more reasonable.  So that the long paths shrink in more than
> the short paths.
> To use a expansion term use the special "reff" variable which stands for
> the "effective r" i.e. the effective half path length.

       I did this and it did help my reduced chi, but I only needed one delr.  
It didnt seem to make a difference having two.  Also, don't forget you have 
to "define" when using equations, I got an error message when I used "set."

Current Results:
     Chi-square                  =    4121.564440839
     Reduced Chi-square          =     390.207284340

     Guess parameters +/- uncertainties  (initial guess):
  amp             =     0.7738890   +/-      0.0616540    
  e0              =     1.2375470   +/-      0.8909140     
  ss              =     0.0032920   +/-      0.0005050      
  e0_1            =    -5.3762680   +/-      1.4964040    
  alpha           =    -0.0044720   +/-      0.0019360    (-0.0100)

There are still some negative values, I guess thats ok?  

        Mucho Thanks , Dan 

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