Dear Prof. Peter and Experts This is with some more information: To put a joint paper on complex Metal-organic halide perovskites, I am trying to reproduce some experimental results measured by my collaborator.
For my complex system, I got low frequency dielectric constant value of ~5.6 (at 0.013 eV) 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). In literature the reported static and optical dielectric constants for the system are in the range of 17-24 and 4.5-6.5 respectively using DFT. In my case the zero frequency dielectric constant (~ 5.6) is in tune with the optical dielectric constants (4.5-6.5). I think my value ~5.6 should be in the range of 17-24. *Is it so?* Please help me to understand it. I used PBE functional with 4x4x4 k mesh. I reduced rmt by 5% and then rmt for Pb and I were reduced by a factor of 0.3. I have doubt here?? My band gap is in reasonable agreement with the experimentally observed band gap (1.57eV) +/- 0.1. 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 (18) then much better exciton binding energies come out. What can be an mistake that I may did in calculation? or may it be a reason of the device fabrication because for experimental part some p-i-n and n-i-p type device has been framed? Kind regards Bhamu
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