[Wien] SOC and U calculation

[Gavin Abo]

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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