[Ifeffit] Fitting Commercial Molybdenum Disulfide

[dmc at pdx.edu]

Mike & list, 

      Where can I find a reasonable model for my delr terms, if I do assume 
that the bond angles are changing/there is no isotropic expansion?  Is there a 
description somewhere in the archives that I could look at?  

      Creating different sigma squared parameters for each path did help the R-
Factor somewhat, but not the reduced chi.  Here's some data:


Fit with seperate sigma's:  

    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








Fit without (original):


Independent points          =      14.312500000
Number of variables         =       4.000000000
Chi-square                  =    6562.747150128
Reduced Chi-square          =     636.387602437
R-factor                    =       0.032979787
Measurement uncertainty (k) =       0.000181935
Measurement uncertainty (R) =       0.004860095
Number of data sets         =       1.000000000


Guess parameters +/- uncertainties  (initial guess):
  e0_1            =    -4.0720130   +/-      1.9194050    (guessed as -4.072009 
(1.919404))
  ss              =     0.0046360   +/-      0.0004110    (guessed as 0.004636 
(0.000411))
  e0              =     1.7659560   +/-      1.1543880    (guessed as 1.765958 
(1.154388))
  alpha           =     0.0010900   +/-      0.0028430    (guessed as 0.001090 
(0.002843))

Def parameters:
  delr_1          =     0.0043250

Set parameters:
  amp             =  0.7


Correlations between variables:
        e0_1 and alpha      -->  0.8416
          e0 and alpha      -->  0.8045
        e0_1 and e0         -->  0.7141
All other correlations are below 0.25