[Wien] regarding exciton binding energies and dielectric constant [updated]

Dr. K. C. Bhamu kcbhamu85 at gmail.com
Thu Nov 10 18:26:43 CET 2016


ohhh, sorry Prof. Peter.

(sp) was included by mistake. I forgot to delete it.

For Pb(5p): When I initialized the case I for one 5P state as core(T) and
other as valance (F).
The total charge leakage (not in the initialization bu it was observed in
the *.outputst file) was 0.00068 with -6.0 ecut and with -7.5 it was
0.000126. So I thought it would be better it I use -7.5 ecut.

However, I will now use -ecut as -6.0.

I think now the step I am going to follow are fine??


One query was unanswered:

how iqtlsave will change the calculation if I choose it as "0"?

Bhamu

On Thu, Nov 10, 2016 at 10:35 PM, Peter Blaha <pblaha at theochem.tuwien.ac.at>
wrote:

> Why would you do a runsp_lapw for a non-magnetic system ???
>
> Spin-orbit is also active for a non-magnetic material.
>
> Don't mix up  spin-polarization with spin-orbit ....
>
> PS: I'm also not sure why you want to include the Pb-5p state as valence
> ?? I don't think you have to use so small Pb spheres that you get core
> leakage ?? And with Pb-5p as core you have the full SO-splitting inluded,
> ....
>
>
>
> 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://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at
>> /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
>> <pblaha at theochem.tuwien.ac.at <mailto:pblaha at 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 at zeus.theochem.tuwien.ac.at
>>                 <mailto:Wien at zeus.theochem.tuwien.ac.at>
>>                 http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
>>                 <http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien>
>>                 SEARCH the MAILING-LIST at:
>>                 http://www.mail-archive.com/wi
>> en at zeus.theochem.tuwien.ac.at/index.html
>>                 <http://www.mail-archive.com/w
>> ien at zeus.theochem.tuwien.ac.at/index.html>
>>
>>
>>
>>         _______________________________________________
>>         Wien mailing list
>>         Wien at zeus.theochem.tuwien.ac.at
>>         <mailto:Wien at zeus.theochem.tuwien.ac.at>
>>         http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
>>         <http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien>
>>         SEARCH the MAILING-LIST at:
>>         http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/
>> index.html
>>         <http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at
>> /index.html>
>>
>>
>>     --
>>     ------------------------------------------------------------
>> --------------
>>     Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
>>     Phone: +43-1-58801-165300             FAX: +43-1-58801-165982
>>     Email: blaha at theochem.tuwien.ac.at
>>     <mailto:blaha at theochem.tuwien.ac.at>    WIEN2k: http://www.wien2k.at
>>     WWW:   http://www.imc.tuwien.ac.at/staff/tc_group_e.php
>>     <http://www.imc.tuwien.ac.at/staff/tc_group_e.php>
>>     ------------------------------------------------------------
>> --------------
>>     _______________________________________________
>>     Wien mailing list
>>     Wien at zeus.theochem.tuwien.ac.at <mailto:Wien at zeus.theochem.tuw
>> ien.ac.at>
>>     http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
>>     <http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien>
>>     SEARCH the MAILING-LIST at:
>>     http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/
>> index.html
>>     <http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at
>> /index.html>
>>
>>
>>
>>
>> _______________________________________________
>> Wien mailing list
>> Wien at 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
>> en at zeus.theochem.tuwien.ac.at/index.html
>>
>>
> --
> --------------------------------------------------------------------------
> Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
> Phone: +43-1-58801-165300             FAX: +43-1-58801-165982
> Email: blaha at 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 at 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
> en at zeus.theochem.tuwien.ac.at/index.html
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://zeus.theochem.tuwien.ac.at/pipermail/wien/attachments/20161110/997312c0/attachment.html>


More information about the Wien mailing list