[Wien] regarding exciton binding energies

[Dr. K. C. Bhamu]

 Dear Wien2k Prof. Blaha and other Wien2k experts,
To put a joint paper on complex Metal-organic halide perovskites, I am
trying to reproduce some experimental results measures by my collaborator.

For my complex system, I got low frequency dielectric constant value of
~5.6 and the calculated the exciton binding energy  ~0.087 - 0.095 eV  (85
-97 meV). This is too high because the measurements here get about 13 meV
and a 1-2 transition of ~9.9 meV (measured).

I used PBE functional with 4x4x4 k mesh. My band gap is in perfect tune
with the experimentally observed band gap (1.57eV).

The problem may be that my epsilon value (~5.6) is too low and I looked up
our local measured value of ~18 for the low frequency part. If I use this
value then much better exciton binding energies come out.


What can be an mistake that I may did in calculation? or it may be a reason
of the device fabrication because for experimental part some p-i-n and
n-i-p type device has been framed.


Sincerely

Bhamu
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