I have some experience using WIEN2k for metal organic halide perovskites.

`PBE without SOC gets the correct band gap for CH3NH3PbI3 (which I assume`

`is the compound Dr. Bhamu is studying) because of a "fortuitous" error`

`cancellation between using PBE and ignoring SOC. This is reasonably well`

`known and has been studied in detail in several manuscripts. SOC+PBE`

`results in a significantly underestimated band gap, as one might expect.`

`I assume Dr. Bhamu is using the calculated low frequency dielectric`

`constant (e*), and the calculated effective mass (m*) to estimate the`

`binding energy using the simple Mott-Wannier model: E_ex = m*/e^2 (13.6)`

`eV .`

`SOC does modify the shape of the bands near the gamma-point (I believe`

`it reduces the effective mass), and SOC also influences the dielectric`

`constant. So I think perhaps including SOC and using a scissors`

`operation with OPTIC to get the correct band gap may be the most`

`straight-forward (if not completely ab initio) method.`

`Have you looked at F. Brivio, et al., Phys. Rev. B 89 155204 (DOI:`

`10.1103/PhysRevB.89.155204)?`

`They go into some detail about different approaches, it may be helpful`

`for your present situation.`

Regards, -John McLeod So I do not think SOC can be On 2016-11-10 10:02 PM, Peter Blaha wrote:

I'm not the expert on that topic, but I think you mix up the twodielectric constants, which could be a semantic problem. To comparewith a classic experiment, you may need to obtain the ioniccontribution to the dielectric constant, which as far as I know can bedone using BERRYPI.Other comments:To obtain the "correct" band gap using PBE is very "unusual". For mostmaterials (but of course there could be exemptions) the PBE band gapsshould be ~50% smaller than experiment.Pb ??? this is very "relativistic" ! Did you consider spin-orbitcoupling ?And last but not least, I have no idea how you calculate excitonbinding energies from a single particle spectrum. We would do thisusing BSE calculations, but your system is probably too complicatedfor this.Am 10.11.2016 um 14:26 schrieb Dr. K. C. Bhamu:Dear Prof. Peter and Experts This is with some more information: To put a joint paper on complex Metal-organic halide perovskites, I amtrying to reproduce some experimental results measured by mycollaborator.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 _______________________________________________ Wien mailing list Wien@zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wienSEARCH the MAILING-LIST at:http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html

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