[Ifeffit] Third cumulant in DWF

Ping, Yuan ping2 at llnl.gov
Mon Apr 4 16:25:39 CDT 2011

Thanks, Bruce.

Does the math expression in IFEFFIT include the term -4k*sigma2*(1/labmda
+1/R) in the phase? If yes, the 1st cumulant is sigma1= R+dR. If no, sigma1=
R+dR+2*sigma2*(1/labmda +1/R). It this correct?


On 4/1/11 2:18 PM, "Bruce Ravel" <bravel at bnl.gov> wrote:

> On Friday, April 01, 2011 05:03:17 pm Ping, Yuan wrote:
>> Dear IFEFFIT experts:
>> Is it possible to add a k^3 term in the phase for fitting to take into
>> account anharmonic effect? The fitted coefficient will be proportional to
>> the 3rd cumulant of Debye-Waller factor. I work with high-temperature
>> high-pressure systems where anharmonic effect is not negligible.
>> Thanks.
>> Yuan Ping
> Hi Yuan,
> Here is the relevant page from the Ifeffit reference manual:
>    http://cars9.uchicago.edu/~ifeffit/refman/node51.html
> You want to use the "3rd" path parameter, which adds a term
> proportional to C3*k^3 to the sine function in the exafs equation.
> See the attached figure for the place in Artemis where this parameter
> is introduced.
> HTH,
> B

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