[Pw_forum] IFC file convention clarification

[Navaneetha Krishnan]

Hi,

I am trying to calculate the IFCs for a FCC lattice (Al) for a few nearest
neighbours. I was following a set of threads, which led me to this one :

http://www.democritos.it/pipermail/pw_forum/2009-August/013613.html

Could someone elaborate on the statement (in this webpage),

"Notice also that the force constant grid is written as these were
periodic ...
so in a 4x4x4 grid R(1,1,1) = 0,  R(2,1,1,) = a1,  and  R(4,1,1)=-a1"?

More specifically, what is R(3, 1, 1) in this case?
Thanks a lot!
--
Navaneeth
Caltech
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