[Ifeffit] Fitting Commercial Molybdenum Disulfide

[Michael A Groves]

Hey Dan,

I only meant if you use the same alpha for all paths, you're assuming an isotropic expansion.  Different alphas is one way to get rid of that.

One other thing I noticed-- in your first message, it says the r-range you used in the fit is the default-- 1<r<3.  However, your longest Mo-S path is almost 4 angstroms long.  Have you thought about adjusting the range that you're fitting-- maybe to r somewhere over 4?

Cheers,
Mike


On Fri, 29 Oct 2004 dmc at pdx.edu wrote:

> 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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