[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
graph.
> 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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