I am trying to calculate the gap re-normalization upon electron-phonon coupling effects, and
in many of the systems i am working on (simple systems), i see that in the dynamical approach
the Z factors are pretty small and far from 1. That would mean that the expansion of
the phonon-mediated self-energy around the bare energies is not justified.
What is the remedy to cure this problem ?
I see in this publication http://www.nature.com/articles/ncomms11327
that although the Z factor (Z=0.64, and even smaller for lower lying occupied states)
is small, people still keep calculating !
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