[QE-users] Eigenvalues, strain study. The V(G=0) reference.

[Lucas Nicolás Lodeiro Moraga]

Hi QE users!

I am studying the effect of the strain over the eigenvalues of VBM and CBM
levels, my system is a cubic metal oxide semiconductor.
My doubt born about the fact: V(G=0) = (1/V) sum sub u alpha sub u
When I change the cell constant, the volume change, but not the alphas,
because i use the same number, type and pseudopotential for atoms. Then the
change in V(G=0) is only for the volume change.
I think that in order to compare the eigenvalues, I need to fix the V(G=0)
reference, to use the same.

I guess to ways to do that:
1.- Known the alphas values for each pseudopotential and atom, then i can
fix the reference by the volume change factor, and with the diference move
the eigenvalues to the same reference. But I do not know where the alpha
values are in the pseudopotential information. I guess it can calculated by
a extrapolation study for an atom in a big cell and the change of vacuum
level with the size of the cell... but that is a big work.
2.- Compare the Volume-Eigenvalue product between diferent cell constant,
the reference for this magnitude is the "sum alphas", the same value for
each cell constant. But in this case I can not know the quantitative change
in the eigenvalues.

Does anyone know any other way to make this comparison?
Do both methods make sense for comparison?
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