[Ifeffit] Debye model on Artemis

[Bruce Ravel]

On Wednesday 12 May 2010 01:59:02 pm Kleber Daum Machado wrote:
> Hi Matt,
> 
> Concerning the third cumulant, my problem is to use a particular model
> for it. Some articles (Frenkel and Rehr, PRB 48 (1993) 585; Araujo et
> al, PRB 74 (2006) 184102) show how to use the Einstein model on Artemis,
> since these articles show the expressions that should be defined for
> sigma^2(T) and C3(T) for this model in Artemis (eqs. 11 and 18 of
> Frenkel and eqs. 2 and 3 of Araujo). In fact, I have already tested them
> on my analysis, using the eins function for sigma^2 and defining the
> C3(T) expression given in those articles in Artemis. I'd like to test
> Debye model too, and my problem is to use Debye model for sigma^2(T) and
> C3(T). For sigma^2(T) Artemis has the debye function already predefined.
> I'd like to use/write an expression for C3(T) considering Debye model,
> but I didn't find anything about such expression on the literature.
> 

The paper by Frenkel and Rehr has formulas in it relating the
cumulants to other parameters, like sigma^2 and an expansion
coefficient.  You can write any math expression you want as the value
for a path parameter.  Indeed, the eins function is not very
complicated and could easily be implemented as a path parameter math
expression.  But eins is a common one, so Matt included it in
Ifeffit.  Ifeffit (and hence Artemis) don't have any special functions
for implementing what you want, but the beauty of Ifeffit is that you
get to write down any math expression that embodies the physics of
what you are trying to measure.  So, if you have a cumulant model in
mind -- just do it!

B

-- 

 Bruce Ravel  ------------------------------------ bravel at bnl.gov

 National Institute of Standards and Technology
 Synchrotron Methods Group at NSLS --- Beamlines U7A, X24A, X23A2
 Building 535A
 Upton NY, 11973

 My homepage:    http://xafs.org/BruceRavel
 EXAFS software: http://cars9.uchicago.edu/~ravel/software/exafs/