[Wien] spin-orbit (PBE and mBJ) for perovskites
Mikhail Nestoklon
nestoklon at mail.ru
Tue Dec 10 13:40:33 CET 2019
Thank you.
Recently I tried to check also PbSe and there I saw this problem. With RLOs when I go above de=8 the total energy starts to increase and SO also behaves strangely. I understood that there is a problem with RLO and tried to do the calculations without RLO. From your answers I conclude that it was a bad decision, RLO are needed, but «de» should be limited.
And what indicates that I need RLOs for the cases where it is not completely straightforward? Should I try to check the figure like the Fig1 in Kuneš et al [PRB, 64, 153102 (2001)], and if I see similar behavior, then I definitely need RLO? Or just «6p elements beginning with Hg and actinides» as mentioned in Singh and Nordstrom book?
Sincerely yours,
Mikhail Nestoklon
>Вторник, 10 декабря 2019, 10:46 +03:00 от Peter Blaha <pblaha at theochem.tuwien.ac.at>:
>
>Don't go above EMAX=10 for SO calculations with RLOs.
>
>On 12/9/19 9:32 PM, Mikhail Nestoklon wrote:
>> Dear Prof. Blaha,
>> Thank you for clarification. I think, now I more or less understand what
>> is happening.
>> 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?
>> Sincerely yours,
>> Mikhail Nestoklon
>>
>> Понедельник, 9 декабря 2019, 19:02 +03:00 от Peter Blaha
>> < pblaha at theochem.tuwien.ac.at >:
>> Hi,
>>
>> Fist of all: The RLOs (p-1/2)-LOs were originally designed to improve
>> the SO splitting of semicore states. There it makes a big difference and
>> is essential to converge E-tot in a meaningful way.
>>
>> (By meaningful I do not mean the absolute number as you tested it, but
>> an E-tot difference of 2 calculations at eg. 2 volumes).
>>
>> This can be best seen if you compare these semicore eigenvalues with the
>> eigenvalues of case.outputst, where the fully-relativistic splitting can
>> be found and compared.
>>
>> You can also add it in a case like Pb (usually, Pb does not have
>> semicore p-states), but the effect MUST be small.
>>
>> Most importantly, you MUST NOT have a too large E-max, because when the
>> spurious LO-eigenvalues of the APW+lo method enter in the spectrum at
>> high energy, you may get a problem as indicated below:
>>
>> I checked this for a free Pb-atom (in a big box).
>>
>> lapwso with Emax=10 gives:
>>
>> -1.5996189 -1.5996189 -1.5996189 -1.5996189 -1.4111046
>> -1.4111046 -1.4111046 -1.4111046 -1.4110328 -1.4110328
>> -0.8489490 -0.8489490 -0.3028265 -0.3028265 -0.2040009
>> -0.2040009 -0.2040009 -0.2040009 -0.0106114 -0.0106114
>>
>> while with EMAX=15 I get 6 spurious ghostbands ("bad Pb-5p states):
>> -8.2276000 -8.2276000 -3.1336676 -3.1336676 -3.1336591
>> -3.1336591 -1.6001880 -1.6001880 -1.6001880 -1.6001880
>> -1.4113465 -1.4113465 -1.4113464 -1.4113464 -1.4112735
>> -1.4112735 -0.8489490 -0.8489490 -0.2886641 -0.2886641
>> -0.2000960 -0.2000960 -0.2000960 -0.2000960 -0.0106114
>>
>> The SO-splitting of 6p states in the Pb atom is 0.109 Ry, while the
>> "good" lapwso calculations yield 0.099, but the "bad ones only 0.088
>> Without the RLO the SO splitting is 0.092, so still better than the
>> "bad" calculation.
>>
>> Eventually one can avoid this switching back to LAPW for the Pb-p
>> states.
>>
>> Peter Blaha
>>
>> On 12/9/19 3:30 PM, Mikhail Nestoklon wrote:
>> > Dear Dr. Tran,
>> > Thank you for the suggestion. Indeed, for CsPbCl3 I get very similar
>> > values (0.70 for PBE-SO and 1.67eV for TB-mBJ) and if I add RLO on Pb
>> > for CsPbI3 at least for PBE-SO I have something close to value
>> given in
>> > Jishi.
>> > However, now I have a general question. How to understand that I
>> need to
>> > add RLO in this situation? Should I just try to add RLO on heavy
>> atoms
>> > and if the result changes prefer the values given by +RLO
>> calculations?
>> > Or I had to suspect that I need to add RLO when realized that the
>> result
>> > does not converge until de>15?
>> > Sincerely yours,
>> > Mikhail Nestoklon
>> >
>> > Пятница, 6 декабря 2019, 0:39 +03:00 от "Tran, Fabien"
>> > < fabien.tran at tuwien.ac.at </compose?To=fabien.tran at tuwien.ac.at>
>> </compose?To=fabien.tran at tuwien.ac.at>>:
>> >
>> > Hi,
>> >
>> > Some time ago I did calculations on CsPbCl3 and I could reproduce
>> > Jishi's results reasonably well except the one in the 1st
>> > column("GGA") which is probably wrong. I got 0.70 eV (0.71 eV from
>> > Jishi) for "GGA+SOC", 1.68 eV (1.59 eV from Jishi) for TB-mBJ and
>> > 2.86 eV (2.83 eV from Jishi) for "present". The only special
>> > requirement that was needed is a p1/2 LO on Pb. I used RKMAX=9 and
>> > de=10 in case.in1. The bug reported here
>> >
>> >
>> http://zeus.theochem.tuwien.ac.at/pipermail/wien/2019-November/029882.html
>> >
>> > is active but has very small effect of 0.01 eV for GGA+SOC. Try
>> > CsPbCl3 instead (struct and inso are attached).
>> >
>> > FT
>> >
>> >
>> ------------------------------------------------------------------------
>> > *From:* Wien < wien-bounces at zeus.theochem.tuwien.ac.at
>> </compose?To=wien%2dbounces at zeus.theochem.tuwien.ac.at>> on behalf of
>> > Mikhail Nestoklon < nestoklon at mail.ru </compose?To=nestoklon at mail.ru>>
>> > *Sent:* Thursday, December 5, 2019 8:21 PM
>> > *To:* A Mailing list for WIEN2k users
>> > *Subject:* [Wien] spin-orbit (PBE and mBJ) for perovskites
>> > Dear wien2k community,
>> > I plan to do some DFT calculation of inorganic perovskites using
>> > WIEN2k (19.1 with some patches except the last one for RLO).
>> > I’ve started from attempt to reproduce the values from Jishi et al.,
>> > JPCC 118, 28344 (2014), but can not get the numbers given in Table 2
>> > even for cubic CsPbI_3. The difference seem to stem from the
>> spin-orbit.
>> > What I did:
>> > Using the file in attachment (I use the lattice constant given in
>> > table 1 and R_MT indicated in the text) I do
>> > $ init_lapw -b -vxc 13 -rkmax 9.0 -lvns 6 -fftfac 4 && x kgen
>> > (14x14x14) && run_lapw -ec 0.00001 -cc 0.0001
>> > I use -lvns 6, the difference with the result using standard value
>> > is small, in Jishi et al. it is mentioned that l_{max}=10 which is
>> > default, assuming they might have meant lvns I tried lvns=10, the
>> > difference with lvns=6 is close to zero. I also tried to put Pb p3/2
>> > orbitals to core (if I put P1/2 to valence the result is strange,
>> > but this is a separate question) and see no difference.
>> > For k-mesh I check the convergence and see that for 14x14x14 the
>> > total energy convergence is below 1mRy and GAP is below 1 meV which
>> > is fine, so I am using this k mesh.
>> > Then I check the RKMAX convergence. For Rmt*Kmax =9 without
>> > spin-orbit I get the same number as in Table 2, but I see that this
>> > number is not fully converged: if I increase RKMAX further the total
>> > energy decreases for 8mRy and gap increases for almost 6 meV. I find
>> > it acceptable to use RKMAX=12: only then it is <1mRy and ~1meV for
>> > total energy and gap respectively. The gap with these numbers is
>> > 1.329meV which is 5 meV different from Table 2, this difference is
>> > probably acceptable.
>> > However, when I switch on the spin-orbit, the difference is huge.
>> > With the default values (I only increase llmax, however it does not
>> > change much) I get GAP about 0.269meV, which is almost 4 times
>> > different from the value given in Jishi et al. Table 2. As the SO
>> > value depends on de (in case.in1), I increase this parameter and
>> > check the value of GAP and also spin-orbit splitting of conduction
>> > and valence band (difference between energies of Gamma_8 and Gamma_7
>> > in R point). GAP and spin-orbit in conduction band fully (below
>> > 1meV) converge only when de=15. Still, the band gap is 0.259eV which
>> > is too far from value given in Jishi et al.
>> > The RLO (I tried to add it on Cs, as for Pb it should be useless
>> > [1]) does not help
>> > With the same parameters I do the mBJ run (TB-mBJ). As expected, the
>> > gap increases, but up to 0.722 eV which is two times different from
>> > the value given in Jishi et al.
>> > I did not try to change R_MT: I use the value given in their paper.
>> > The fact that I do reproduce the number given for PBE without
>> > spin-orbit indicates that I hardly did any mistake in the structure.
>> > However, the difference in the numbers with spin-orbit is too large
>> > to be explained by unconverged results, both on my and their side.
>> > Could you help me to understand, how can I reproduce their results?
>> > Thank you in advance.
>> > Sincerely yours,
>> > Mikhail Nestoklon
>> > [1]
>> >
>> https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg17828.html
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>>
>> --
>>
>> P.Blaha
>> --------------------------------------------------------------------------
>> 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
>> </compose?To=blaha at theochem.tuwien.ac.at> WIEN2k: http://www.wien2k.at
>> WWW: http://www.imc.tuwien.ac.at/TC_Blaha
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>
>--
>
> P.Blaha
>--------------------------------------------------------------------------
>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
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