Thank you Professor Peter and McLeod for your nice explanation. I have to go through the paper and then I can make a better statement. You are right Mcleod, it is orthrohombic MAPbI3 structure.
Dear Prof. Peter, It is reported by Tran that mBJ is not good for effective masses: http://firstname.lastname@example.org/msg10700.html However as per your suggestion I am going to follow below steps. I have limited wall time so I need your comment on below steps: For now (to save walltime), Please make any comment in any step if I am going wrong: What I am using: *Goal*: mBJ+SO A. 1. PBE as PBE gave better band gap so it may be useful. In the suggested paper they did not used PBE function instead they used PBEsol. 2. 144 k-points generated, ndiv= 11 7 11 (I think it is more than sufficient). 3. ecut -7.5 to consider Pb (5P) state as valence. 4. R-MT*K-MAX = 3 (as I have "H" here). 5. gmin = 9.23077, gmax = 20.00000 6. SP calculation ? No (as it is not a magnetic system). B. run a regular scf "min -j 'run_lapw -p -i 40 -ec 0.0001 -cc 0.0001 -fc 1' Tt will give me a relaxed structure with optimised a,b and c. C. 1. save_lapw case_bhamu 2. init_mbj_lapw 3. run_lapw -i 1 4. run_mbj_lapw "run-lapw -p -i 80 -ec 0.0001 -cc 0.001" (as per your recent comment on my post that we do not need -fc if we have done in regular scf) 5. save_lapw case_mBJ D. 1. initso_lapw 2. runsp_lapw -so -p -i 40 -ec 0.0001 -cc 0.0001' Fine ???? I am using both step C and D differently because Dr. Tran suggested for the same ( http://email@example.com/msg03843.html) One more question: how iqtlsave will change the calculation if I coose it as "0"? Kind regards ------------------------------------------------ Dr. K. C. Bhamu (UGC-Dr. D. S. Kothari Postdoc Fellow) Department of Physics Goa University, Goa-403 206 India Mob. No. +91-9975238952 On Thu, Nov 10, 2016 at 8:00 PM, Peter Blaha <pbl...@theochem.tuwien.ac.at> wrote: > Very good explanation. > > So you should probably use SO + mBJ and see what comes out then .... > (you should get again a good band gap, although effective masses are not > necessarily improved by mBJ ...) > > Am 10.11.2016 um 15:24 schrieb John McLeod: > >> 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 two >>> dielectric constants, which could be a semantic problem. To compare >>> with a classic experiment, you may need to obtain the ionic >>> contribution to the dielectric constant, which as far as I know can be >>> done using BERRYPI. >>> >>> Other comments: >>> To obtain the "correct" band gap using PBE is very "unusual". For most >>> materials (but of course there could be exemptions) the PBE band gaps >>> should be ~50% smaller than experiment. >>> >>> Pb ??? this is very "relativistic" ! Did you consider spin-orbit >>> coupling ? >>> >>> And last but not least, I have no idea how you calculate exciton >>> binding energies from a single particle spectrum. We would do this >>> using BSE calculations, but your system is probably too complicated >>> for 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 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 >>>> >>>> >>>> >>>> >>>> _______________________________________________ >>>> Wien mailing list >>>> Wien@zeus.theochem.tuwien.ac.at >>>> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien >>>> SEARCH the MAILING-LIST at: >>>> http://firstname.lastname@example.org/index.html >>>> >>>> >>> >> _______________________________________________ >> Wien mailing list >> Wien@zeus.theochem.tuwien.ac.at >> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien >> SEARCH the MAILING-LIST at: >> http://email@example.com/index.html >> > > -- > -------------------------------------------------------------------------- > Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna > Phone: +43-1-58801-165300 FAX: +43-1-58801-165982 > Email: bl...@theochem.tuwien.ac.at WIEN2k: http://www.wien2k.at > WWW: http://www.imc.tuwien.ac.at/staff/tc_group_e.php > -------------------------------------------------------------------------- > _______________________________________________ > Wien mailing list > Wien@zeus.theochem.tuwien.ac.at > http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien > SEARCH the MAILING-LIST at: http://www.mail-archive.com/wi > e...@zeus.theochem.tuwien.ac.at/index.html >
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