Thanks a lot Scott , I got that how to change ss for difeerent path by using the function debye(temp, thetad).But I am not getting the same result in case of delr . I took the different parameter as follow :

guess amp 1

def delr alpha*reff

guess enot 0

def ss debye(temp,thetad)

set alpha .0002

set thetad 343

set temp 298

But I am not getting a very good fit. The value of debye temperature is 343 for Cu( Kittel book) but I got to know that some persons even guessed the value of thetad as 285+-16 . I am not getting that how we can guess the value of alpha and thetad . Also I am not getting the value of Ei, 3rd and 4th cumulant in the fit results . So How can I get the value of these parameters in the fit results .

With thanks

Abhijeet Gaur