[Ifeffit] cumulant/rdf question

grant bunker bunker at iit.edu
Tue Jul 15 17:32:12 CDT 2008


re the cumulant  <--> rdf connection
This isn't a general solution, but it may work well for your system.
A poisson distribution (x-x)^s Exp[-a (x-x0)] is a pretty flexible for  
moderately skewed distributions, permitting variable C2 and C3 by  
adjusting parameters s and a. For large s and small a the distribution  
approaches a gaussian.
Expressions for cumulants etc are in Yang et al, JNCS Volume 210,  
Number 2, March 1997

have fun - gb

> matt,
>
> I have a problem with an exafs analysis:
> from the exafs analysis (with feffit2.98) of the first shell of a  
> disordered
> system
> I get the first three cumulants.
> now, I wander how can reconstruct from them the radial distribution  
> function
> which is the best solution? I have tried with the skew-normal  
> distribution,
> but for the high skewness (ratio of third cumulant to sigma3)
> values I get - that is around 2.5 - it is not well defined.
> Do you have a suggestion?
> Thanks,



More information about the Ifeffit mailing list