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

[Mikhail Nestoklon]

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 >:
>  
>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 > on behalf of Mikhail Nestoklon < 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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