[Ifeffit] Debye model on Artemis

[Kleber Daum Machado]

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.

Kleber