[Wien] spin-orbit (PBE and mBJ) for perovskites
Peter Blaha
pblaha at theochem.tuwien.ac.at
Tue Dec 10 08:46:13 CET 2019
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
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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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