[Wien] How to find the exact value of infinte epsilon?

[Atefe Marasi]

Dear Xavier

Thank you for your prompt reply.

> Infinite epsilon means that you extrapolate ...

Do you mean that infinite epsilon (epsilon_oo) is nothing more than epsilon
zero (epsilon_0)?

> You must plot the real part...
I have plotted the real part of epsilon in z direction(for BaTiO3), as
would be seen from the following link:
https://imgurl.ir/uploads/p793339_infinite_epsilon.jpg
As expected, the above figure shows that the real part of the epsilon tends
to unity at high frequency. From this plot, the epsilon_0 is about 6.5, but
I am still not sure that whether infinite epsilon is really equal to
epsilon_zero (epsilon_oo =? epsilon_0).

> You must be careful because if you have a band gap and a bad description
of the gap value ...

Thank you for this hint. I will try to obtain a suitable band gap by TB-mBJ
functional. However, at this step, I need to find out the difference
between epsilon_oo and epsilon_0. In my opinion, which I am not sure about
it, epsilon_00 would be evaluated at infinite energy, while epsilon_0 would
be evaluated at zero energy, as deduced  from their names.
Thank you for your nice cooperation.

Best Regards
Atefe Marasi
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