[Wien] spin-orbit (PBE and mBJ) for perovskites

[Peter Blaha]

Dear WIEN2k users,

when using a RLO in lapwso, do NOT use too large Emax in lapw1.

When one includes "all" eigenvalues (i.e. those high-lying ones from the 
LO basis, which are significantly larger than the "APW" eigenvalues) and 
then adds a RLO, ghostbands and unphysical states in the occupied space 
may occur.

Am 05.12.2019 um 20:21 schrieb Mikhail Nestoklon:
> 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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-- 
--------------------------------------------------------------------------
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/tc_blaha-------------------------------------------------------------------------