<div dir="ltr"><div><div><div><div><div><div><div><div><div>Thank you Professor Peter and McLeod for your nice explanation.<br></div>I have to go through the paper and then I can make a better statement.<br></div><div>You are right Mcleod, it is orthrohombic MAPbI3 structure.<br><br></div><div>Dear Prof. Peter,<br><br></div><div>It is reported by Tran that mBJ is not good for effective masses:<br><br><a href="http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg10700.html">http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg10700.html</a><br><br></div><div>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:<br></div><div><br></div>For now (to save walltime), Please make any comment in any step if I am going wrong:<br><br></div>What I am using: <br></div><div><b>Goal</b>: mBJ+SO</div><div>A.<br></div>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.<br>2. 144 k-points generated, ndiv= 11 7 11 (I think it is more than sufficient).<br></div>3. ecut -7.5 to consider Pb (5P) state as valence.<br>4. R-MT*K-MAX = 3 (as I have "H" here).<br>5. gmin = 9.23077, gmax = 20.00000<br></div>6. SP calculation ? No (as it is not a magnetic system).<br></div><br>B. <br>run a regular scf "min -j 'run_lapw -p -i 40 -ec 0.0001 -cc 0.0001 -fc 1' <br></div><div>Tt will give me a relaxed structure with optimised a,b and c.<br></div><div><br>C. <br>1. save_lapw case_bhamu <br></div><div>2. init_mbj_lapw<br></div><div>3. run_lapw -i 1<br></div><div>4. run_mbj_lapw<br></div><div> "run-lapw -p -i 80 -ec 0.0001 -cc 0.001" (as per your recent comment on my post that we do not <br> need -fc if we have done in regular scf)<br></div><div>5. save_lapw case_mBJ<br></div><div><br></div><div>D.<br></div><br>1. initso_lapw<br>2. runsp_lapw -so -p -i 40 -ec 0.0001 -cc 0.0001' Fine ????<br><br></div>I am using both step C and D differently because Dr. Tran suggested for the same (<a href="http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg03843.html">http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg03843.html</a>)<br><br><div><div><div><br><div><div><div class="gmail_extra">One more question:<br>how iqtlsave will change the calculation if I coose it as "0"?<br><br>Kind regards<br><br><br clear="all"><div><div class="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><span style="color:rgb(0,0,0)"><br>------------------------------------------------<br>Dr. K. C. Bhamu<br>(UGC-Dr. D. S. Kothari Postdoc Fellow)<br>Department of Physics<br>Goa University, Goa-403 206<br>India<br>Mob. No. +91-9975238952</span></div></div></div></div></div></div></div></div></div></div></div>
<br><div class="gmail_quote">On Thu, Nov 10, 2016 at 8:00 PM, Peter Blaha <span dir="ltr"><<a href="mailto:pblaha@theochem.tuwien.ac.at" target="_blank">pblaha@theochem.tuwien.ac.at</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Very good explanation.<br>
<br>
So you should probably use SO + mBJ and see what comes out then ....<br>
(you should get again a good band gap, although effective masses are not necessarily improved by mBJ ...)<br>
<br>
Am 10.11.2016 um 15:24 schrieb John McLeod:<br>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
I have some experience using WIEN2k for metal organic halide perovskites.<br>
<br>
PBE without SOC gets the correct band gap for CH3NH3PbI3 (which I assume<br>
is the compound Dr. Bhamu is studying) because of a "fortuitous" error<br>
cancellation between using PBE and ignoring SOC. This is reasonably well<br>
known and has been studied in detail in several manuscripts. SOC+PBE<br>
results in a significantly underestimated band gap, as one might expect.<br>
<br>
I assume Dr. Bhamu is using the calculated low frequency dielectric<br>
constant (e*), and the calculated effective mass (m*) to estimate the<br>
binding energy using the simple Mott-Wannier model: E_ex = m*/e^2 (13.6)<br>
eV .<br>
<br>
SOC does modify the shape of the bands near the gamma-point (I believe<br>
it reduces the effective mass), and SOC also influences the dielectric<br>
constant. So I think perhaps including SOC and using a scissors<br>
operation with OPTIC to get the correct band gap may be the most<br>
straight-forward (if not completely ab initio) method.<br>
<br>
Have you looked at F. Brivio, et al., Phys. Rev. B 89 155204 (DOI:<br>
10.1103/PhysRevB.89.155204)?<br>
They go into some detail about different approaches, it may be helpful<br>
for your present situation.<br>
<br>
Regards,<br>
-John McLeod<br>
<br>
So I do not think SOC can be<br>
On 2016-11-10 10:02 PM, Peter Blaha wrote:<br>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
I'm not the expert on that topic, but I think you mix up the two<br>
dielectric constants, which could be a semantic problem. To compare<br>
with a classic experiment, you may need to obtain the ionic<br>
contribution to the dielectric constant, which as far as I know can be<br>
done using BERRYPI.<br>
<br>
Other comments:<br>
To obtain the "correct" band gap using PBE is very "unusual". For most<br>
materials (but of course there could be exemptions) the PBE band gaps<br>
should be ~50% smaller than experiment.<br>
<br>
Pb ??? this is very "relativistic" ! Did you consider spin-orbit<br>
coupling ?<br>
<br>
And last but not least, I have no idea how you calculate exciton<br>
binding energies from a single particle spectrum. We would do this<br>
using BSE calculations, but your system is probably too complicated<br>
for this.<br>
<br>
Am 10.11.2016 um 14:26 schrieb Dr. K. C. Bhamu:<br>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
Dear Prof. Peter and Experts<br>
This is with some more information:<br>
<br>
To put a joint paper on complex Metal-organic halide perovskites, I am<br>
trying to reproduce some experimental results measured by my<br>
collaborator.<br>
<br>
For my complex system, I got low frequency dielectric constant value of<br>
~5.6 (at 0.013 eV) and the calculated the exciton binding energy ~0.087<br>
- 0.095 eV (85 -97 meV). This is too high because the measurements here<br>
get about 13 meV and a 1-2 transition of ~9.9 meV (measured).<br>
<br>
In literature the reported static and optical dielectric constants for<br>
the system are in the range of 17-24 and 4.5-6.5 respectively using DFT.<br>
<br>
In my case the zero frequency dielectric constant (~ 5.6) is in tune<br>
with the optical dielectric constants (4.5-6.5).<br>
<br>
I think my value ~5.6 should be in the range of 17-24. *Is it so?*<br>
Please help me to understand it.<br>
<br>
I used PBE functional with 4x4x4 k mesh. I reduced rmt by 5% and then<br>
rmt for Pb and I were reduced by a factor of 0.3. I have doubt here??<br>
<br>
My band gap is in reasonable agreement with the experimentally observed<br>
band gap (1.57eV) +/- 0.1.<br>
<br>
The problem may be that my epsilon value (~5.6) is too low and I looked<br>
up our local measured value of ~18 for the low frequency part. If I use<br>
this value (18) then much better exciton binding energies come out.<br>
<br>
What can be an mistake that I may did in calculation? or may it be a<br>
reason of the device fabrication because for experimental part some<br>
p-i-n and n-i-p type device has been framed?<br>
<br>
<br>
Kind regards<br>
<br>
Bhamu<br>
<br>
<br>
<br>
<br>
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