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[<selva.nair@gmail.com>]

Hello developers,

I am trying to extract off-diagonal matrix elements of position operator (or a
related 
operator such as d/dk or dH/dk) between ground state wavefunctions from 
Abinit.
If 
I understand it correctly, the "first order eigen value matrix" in _1WF7,8,9
files generated
by a ddk perturbation run would contain this information but I am unable to
find the 
precise meaning of these "eigen values".

In a  ddk perturbation run what exactly is the perturbation? Is it dH/dk? Are
the eigen 
value matrix elements in _1WF7,8,9 that of dH/dk between the zeroth order
wavefunctions?

Also is any one working on ddk and electric field  perturbations with
spin-orbit 
interaction?

Thanks,

Selva