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<div>Dear Prof. Blaha,</div>
<div>Thank you for clarification. I think, now I more or less understand what is happening. </div>
<div>It seems, this issue is very easy to miss. Do you have any practical recommendation how to spot this kind of problem in the calculations of non-trivial material with few atoms?<br>
</div>
<div>Sincerely yours,</div>
<div>Mikhail Nestoklon</div>
<div> </div>
<blockquote style="border-left:1px solid #0857A6; margin:10px; padding:0 0 0 10px;">Понедельник, 9 декабря 2019, 19:02 +03:00 от Peter Blaha <pblaha@theochem.tuwien.ac.at>:<br>
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<div id="style_15759073681404185754_BODY">Hi,<br>
<br>
Fist of all: The RLOs (p-1/2)-LOs were originally designed to improve<br>
the SO splitting of semicore states. There it makes a big difference and<br>
is essential to converge E-tot in a meaningful way.<br>
<br>
(By meaningful I do not mean the absolute number as you tested it, but<br>
an E-tot difference of 2 calculations at eg. 2 volumes).<br>
<br>
This can be best seen if you compare these semicore eigenvalues with the<br>
eigenvalues of case.outputst, where the fully-relativistic splitting can<br>
be found and compared.<br>
<br>
You can also add it in a case like Pb (usually, Pb does not have<br>
semicore p-states), but the effect MUST be small.<br>
<br>
Most importantly, you MUST NOT have a too large E-max, because when the<br>
spurious LO-eigenvalues of the APW+lo method enter in the spectrum at<br>
high energy, you may get a problem as indicated below:<br>
<br>
I checked this for a free Pb-atom (in a big box).<br>
<br>
lapwso with Emax=10 gives:<br>
<br>
-1.5996189 -1.5996189 -1.5996189 -1.5996189 -1.4111046<br>
-1.4111046 -1.4111046 -1.4111046 -1.4110328 -1.4110328<br>
-0.8489490 -0.8489490 -0.3028265 -0.3028265 -0.2040009<br>
-0.2040009 -0.2040009 -0.2040009 -0.0106114 -0.0106114<br>
<br>
while with EMAX=15 I get 6 spurious ghostbands ("bad Pb-5p states):<br>
-8.2276000 -8.2276000 -3.1336676 -3.1336676 -3.1336591<br>
-3.1336591 -1.6001880 -1.6001880 -1.6001880 -1.6001880<br>
-1.4113465 -1.4113465 -1.4113464 -1.4113464 -1.4112735<br>
-1.4112735 -0.8489490 -0.8489490 -0.2886641 -0.2886641<br>
-0.2000960 -0.2000960 -0.2000960 -0.2000960 -0.0106114<br>
<br>
The SO-splitting of 6p states in the Pb atom is 0.109 Ry, while the<br>
"good" lapwso calculations yield 0.099, but the "bad ones only 0.088<br>
Without the RLO the SO splitting is 0.092, so still better than the<br>
"bad" calculation.<br>
<br>
Eventually one can avoid this switching back to LAPW for the Pb-p states.<br>
<br>
Peter Blaha<br>
<br>
On 12/9/19 3:30 PM, Mikhail Nestoklon wrote:<br>
> Dear Dr. Tran,<br>
> Thank you for the suggestion. Indeed, for CsPbCl3 I get very similar<br>
> values (0.70 for PBE-SO and 1.67eV for TB-mBJ) and if I add RLO on Pb<br>
> for CsPbI3 at least for PBE-SO I have something close to value given in<br>
> Jishi.<br>
> However, now I have a general question. How to understand that I need to<br>
> add RLO in this situation? Should I just try to add RLO on heavy atoms<br>
> and if the result changes prefer the values given by +RLO calculations?<br>
> Or I had to suspect that I need to add RLO when realized that the result<br>
> does not converge until de>15?<br>
> Sincerely yours,<br>
> Mikhail Nestoklon<br>
><br>
> Пятница, 6 декабря 2019, 0:39 +03:00 от "Tran, Fabien"<br>
> <<a href="/compose?To=fabien.tran@tuwien.ac.at">fabien.tran@tuwien.ac.at</a> </compose?To=fabien.tran@tuwien.ac.at>>:<br>
><br>
> Hi,<br>
><br>
> Some time ago I did calculations on CsPbCl3 and I could reproduce<br>
> Jishi's results reasonably well except the one in the 1st<br>
> column("GGA") which is probably wrong. I got 0.70 eV (0.71 eV from<br>
> Jishi) for "GGA+SOC", 1.68 eV (1.59 eV from Jishi) for TB-mBJ and<br>
> 2.86 eV (2.83 eV from Jishi) for "present". The only special<br>
> requirement that was needed is a p1/2 LO on Pb. I used RKMAX=9 and<br>
> de=10 in case.in1. The bug reported here<br>
><br>
> <a href="http://zeus.theochem.tuwien.ac.at/pipermail/wien/2019-November/029882.html" target="_blank">http://zeus.theochem.tuwien.ac.at/pipermail/wien/2019-November/029882.html</a><br>
><br>
> is active but has very small effect of 0.01 eV for GGA+SOC. Try<br>
> CsPbCl3 instead (struct and inso are attached).<br>
><br>
> FT<br>
><br>
> ------------------------------------------------------------------------<br>
> *From:* Wien <<a href="/compose?To=wien%2dbounces@zeus.theochem.tuwien.ac.at">wien-bounces@zeus.theochem.tuwien.ac.at</a>> on behalf of<br>
> Mikhail Nestoklon <<a href="/compose?To=nestoklon@mail.ru">nestoklon@mail.ru</a>><br>
> *Sent:* Thursday, December 5, 2019 8:21 PM<br>
> *To:* A Mailing list for WIEN2k users<br>
> *Subject:* [Wien] spin-orbit (PBE and mBJ) for perovskites<br>
> Dear wien2k community,<br>
> I plan to do some DFT calculation of inorganic perovskites using<br>
> WIEN2k (19.1 with some patches except the last one for RLO).<br>
> I’ve started from attempt to reproduce the values from Jishi et al.,<br>
> JPCC 118, 28344 (2014), but can not get the numbers given in Table 2<br>
> even for cubic CsPbI_3. The difference seem to stem from the spin-orbit.<br>
> What I did:<br>
> Using the file in attachment (I use the lattice constant given in<br>
> table 1 and R_MT indicated in the text) I do<br>
> $ init_lapw -b -vxc 13 -rkmax 9.0 -lvns 6 -fftfac 4 && x kgen<br>
> (14x14x14) && run_lapw -ec 0.00001 -cc 0.0001<br>
> I use -lvns 6, the difference with the result using standard value<br>
> is small, in Jishi et al. it is mentioned that l_{max}=10 which is<br>
> default, assuming they might have meant lvns I tried lvns=10, the<br>
> difference with lvns=6 is close to zero. I also tried to put Pb p3/2<br>
> orbitals to core (if I put P1/2 to valence the result is strange,<br>
> but this is a separate question) and see no difference.<br>
> For k-mesh I check the convergence and see that for 14x14x14 the<br>
> total energy convergence is below 1mRy and GAP is below 1 meV which<br>
> is fine, so I am using this k mesh.<br>
> Then I check the RKMAX convergence. For Rmt*Kmax =9 without<br>
> spin-orbit I get the same number as in Table 2, but I see that this<br>
> number is not fully converged: if I increase RKMAX further the total<br>
> energy decreases for 8mRy and gap increases for almost 6 meV. I find<br>
> it acceptable to use RKMAX=12: only then it is <1mRy and ~1meV for<br>
> total energy and gap respectively. The gap with these numbers is<br>
> 1.329meV which is 5 meV different from Table 2, this difference is<br>
> probably acceptable.<br>
> However, when I switch on the spin-orbit, the difference is huge.<br>
> With the default values (I only increase llmax, however it does not<br>
> change much) I get GAP about 0.269meV, which is almost 4 times<br>
> different from the value given in Jishi et al. Table 2. As the SO<br>
> value depends on de (in case.in1), I increase this parameter and<br>
> check the value of GAP and also spin-orbit splitting of conduction<br>
> and valence band (difference between energies of Gamma_8 and Gamma_7<br>
> in R point). GAP and spin-orbit in conduction band fully (below<br>
> 1meV) converge only when de=15. Still, the band gap is 0.259eV which<br>
> is too far from value given in Jishi et al.<br>
> The RLO (I tried to add it on Cs, as for Pb it should be useless<br>
> [1]) does not help<br>
> With the same parameters I do the mBJ run (TB-mBJ). As expected, the<br>
> gap increases, but up to 0.722 eV which is two times different from<br>
> the value given in Jishi et al.<br>
> I did not try to change R_MT: I use the value given in their paper.<br>
> The fact that I do reproduce the number given for PBE without<br>
> spin-orbit indicates that I hardly did any mistake in the structure.<br>
> However, the difference in the numbers with spin-orbit is too large<br>
> to be explained by unconverged results, both on my and their side.<br>
> Could you help me to understand, how can I reproduce their results?<br>
> Thank you in advance.<br>
> Sincerely yours,<br>
> Mikhail Nestoklon<br>
> [1]<br>
> <a href="https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg17828.html" target="_blank">https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg17828.html</a><br>
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<br>
--<br>
<br>
P.Blaha<br>
--------------------------------------------------------------------------<br>
Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna<br>
Phone: <span class="js-phone-number">+43-1-58801-165300</span> FAX: <span class="js-phone-number">+43-1-58801-165982</span><br>
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