[QE-users] dielectric function from turbo_lanczos

[Michal Krompiec]

Hello,
I'm trying to compare refractive index spectra calculated with epsilon.x
and TDDFpT with the turbo_lanczos code. My system is a periodic supercell,
I am using PBEsol functional, Gamma-only sampling and norm-conserving PPs.

>From the output of epsilon.x, I calculate refractive index n as follows:
n =
np.sqrt(np.sqrt(np.square(eps_real_iso)+np.square(eps_imag_iso)+eps_real_iso))
# eps_real_iso and eps_imag_iso are averages of the spatial components of
real and imaginary epsilon

Now, how do I convert the complex susceptibility chi (from the output of
turbo_lanczos) to epsilon? I know that in principle epsilon = 1 + chi, but
then the results don’t make sense. Am I missing some unit conversion or
something else?
Moreover, turbo_lanczos is complaining it hasn’t got enough information to
compute S - what could be the cause of this?

Thanks,
Michal Krompiec
Merck KGaA
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