[Wien] SOC and U calculation

[Muhammad Sajjad]

Dear Gavin
I am highly thankful for the detailed reply. It is quite helping.

True Regards
M. Sajjad

On Wed, Aug 5, 2015 at 3:35 AM, Gavin Abo <gsabo at crimson.ua.edu> wrote:

> I don't know everything about DFT+U+SO calculations, but I will try to
> answer your questions.  See below.
>
> Dear users I am intended to perform FM+U+SOC calculation for Ca2CoSiO7.
> The step that I understood to perform for such calculations are:
> 1. run simple SCF with LDA using spin polarized calculations
> 2. save and run initso_lapw
> it asks about magnetization direction, Emax value, add RLO for NONE/ ALL/
> CHOOSE elements, spin-polarized case, selection of new structure for SO,
> Number of kpoints.
> 3. Import .inorb and .indm from SRC_templates for LDA+U calculation and
> edit them by requirement.
> 4. Finally use command runsp_lapw -p -so -orb -cc 0.0001 -ec 0.0001 -NI.
>
> My queries are:
> a. Is it the right approach for the mentioned calculation?
>
>
> Yes, the approach that you mentioned above looks fine.
>
> b. In second step, can we change magnetization direction?
>
>
> If step 1 came before it, then you can 'set' the magnetization direction
> in step 2.  If you just completed step 4 and are going to back to step 2, I
> think you need to do a save then a restore (i.e., restore_lapw) of the step
> 1 calculation before you should 'change' the magnetization direction using
> initso_lapw.
>
> how much Emax should be increased (default value is 5 Ry)?
>
>
> You should be able to increase it until the output parameter you are
> interested in has converged (i.e., do a convergence test with Emax) [
> https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg02113.html
> ].
>
> Which option is correct for adding RLO?
>
>
> If you don't know when to add them, enter N for NONE for RLO:
>
>
> https://www.mail-archive.com/wien%40zeus.theochem.tuwien.ac.at/msg08381.html
>
> https://www.mail-archive.com/wien%40zeus.theochem.tuwien.ac.at/msg05958.html
>
> https://www.mail-archive.com/wien%40zeus.theochem.tuwien.ac.at/msg11478.html
>
> As it says in the Wien2k 14.2 usersguide on page 120 [
> http://www.wien2k.at/reg_user/textbooks/usersguide.pdf ], RLOs are used
> for elements with semicore p-states:
>
> *We also provide an additional basisfunction, namely a ”relativistic-LO”
> (RLO) with a*
> *p1/2 radial wavefunction, which improves the basis and removes to a large
> degree the dependency*
> *of the results on EMAX and RMT (see Kuneˇs et al. 2001). It is particular
> **helpfull for heavier atoms*
> *with semicore p-states**, but it must not be used for EFG calculations.*
>
> Ca, Co, Si, and O should be relatively 'light' elements in the periodic
> table [ https://en.wikipedia.org/wiki/Chemical_element#Atomic_numbers ].
>
> do we need to increase kpoints (before it was 200 for simple scf)?
>
>
> In the WIEN2k 14.2 usersguide (section 4.5.5 Spin-orbit interaction), it
> mentions that SO can reduce the symmetry depending on how the direction of
> magnetization is chosen.
>
> In the "Notes about spin-orbit (pdf)" file
> (novak_lecture_on_spinorbit.pdf) at
> http://www.wien2k.at/reg_user/textbooks/ (section 4.4), it mentions that
> the reduction in symmetry has the consequence that the irreducible wedge of
> the Brillouin zone must be enlarged.  So generally yes, the number of
> k-points need to be increased for the SO calculation.
>
> How much should you increase the k-points?  You should able to determine
> how many from a convergence test with k-points [
> https://www.beilstein-journals.org/bjnano/content/supplementary/2190-4286-2-45-S1.pdf
> ].
>
> c. Is there any way (like in mBJ we run init_mbj_lapw that imports
> inm_vresp files and makes changes) to import .inorb and .indm file by
> command line?
>
>
> No, I'm not aware of a script like init_mbj_lapw for SO calculations.
>
> You could do programming of your own script to cp and/or edit .inorb and
> indm files. I put such an example script called init_orb_lapw on my github
> page [ https://github.com/gsabo/WIEN2k-Patches/tree/master/14.2 ] (click
> WIEN2k-Patches and Download ZIP).  You may try or modify init_orb_lapw at
> your own risk (it should give some automation to what you have described
> for step 3).
>
> d. Is the final command correct?
>
>
> Yes, the step 4 command looks correct. However, removing the -NI in step 4
> might even help you catch a problem; for example, I think if you forget to
> do a save_lapw, it will indicate that the broyd files exist from a previous
> calculation and give you a few seconds before it automatically removes and
> continues with the new calculation.  Whereas with -NI, it might continue
> with previous broyd files and possibly crash the calculation.
>
> and if someone wants to use GGA+U then simply it is required to run simple
> SCF by GGA and then apply U or any other method?
>
>
> Yes, you can simply run the SCF with GGA selected in case.in0 and then
> apply U.  For example, you could probably even do that between steps 1 and
> 2:
>
> 1a. save -d LDAwithoutSO
> 1b. Select GGA in case.in0
> 1c. runsp_lapw
> 1d. save -d GGAwithoutSO
> 1e. Create .inorb and .indm
> 1f. runsp_lapw -orb
> 1g. save -d GGAUwithoutSO
> 1h. Select LDA in case.in0
>
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>


-- 
Kind Regards
Muhammad Sajjad
Post Doctoral Fellow
KAUST, KSA.
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