Axel, thanks for those references on structure generation. Now, I have much better idea about "which structure(s)" in CE. In the UNCLE code (even though I have not used it), Hart et al always talk about GA approach, but I did not know to what extent ATAT is different! I am glad to know what you said.
But, now I have another question and still regarding CE but this time regarding on-site magnetic moments. Suppose, I do a cluster expansion of bcc Fe-Ni system. If I do a CE of magnetic moment, I would get mean magnetic moment in bcc solid solution! But, how do I get on-site magnetic moment of Fe and Ni as a function of comp in bcc solid solution? Of course, this is what I can do:
(i) define WS radii of Fe and Ni in each ordered structure
(ii) Calculate on-site magnetic moment of Fe and Ni in each ordered structure
(iii) do a CE of on-site magnetic moment of Fe and Ni to get
(iv) on-site magnetic moment of Fe and Ni in bcc solid solution! Is that it?
My intuition tells me it may not be that simple. Please, tell me if you have another idea to solve this problem.
Your idea to calculate the on-site magnetic moments in a solid solution seems completely reasonable IF
the spins are colinear AND have ferromagnetic ordering.
Let us know how it works!
Axel,
That was just a quick idea (CE of on-site magmom) that came off my head, but later I realized that the correlation matrix for on-site magnetic moment (or, any on-site property) may be different! So, I was not entirely sure about the whole approach!
Normally, people do neutron diffraction and report mean magnetic moment in solid solutions. However, occasionally on-site magnetic moments in solid solutions are also reported although far too few as data analysis may not be trivial. So far, I have come across only few papers reporting on-site magnetic moments in solid solutions.
Of course, I will try and let you know if I am satisfied with results, or if I see unusual behavior.
Gautam
Axel,
Just another follow-up. Is it possible to do local cluster expansion, as opposed to what is normally done to calculate the energy of mixing, in ATAT?
