[Wien] Strategy for a large slab with SP and SOC

[Peter Blaha]

No,this is not a good strategy.

 From a converged non-spin-polarized calculation you cannot come 
(easily) to a spin-polarized solution.

So   1) is only good if you want to quote how much more stable a SP 
solution is compared to a non-SP.

2 + 3 is a good practice. You gain insight how large are the changes and 
on what atoms due to SO coupling.

------------------------

In terms of efficiency for large cases, I'd in particular preconverge 
with a course k-mesh and later on refine.

---------------------------

Every runsp cycle starts with a case.clmsum/up/dn file.

These files can come from an initialization, but of course also from any 
prior scf calculation (eg. with lower k-mesh or without SO). Of course, 
a restore_lapw ... gives you all files necessary to run another scf cycle.

-NI would keep old broyden files, but after a "save_lapw" they are gone 
anyway.  -NI is useful if you want to continue a scf, because eg. the 
first runsp stopped after 40 cycles and did not reach convergence yet.

Am 16.06.2023 um 10:44 schrieb pluto via Wien:
> Dear All,
>
> I just would like to confirm the step-by-step convergence strategy for 
> the large slab with SP and SOC (it refers in general to spin-momentum 
> locked non-magnetic TMDC, but can be any other material).
>
> Is the following correct:
>
> 1. Converge without SP and without SOC, and save_lapw e.g. as 
> CONV_NO_SP_NO_SOC so it can be used in another directory or on another 
> computer for the next steps
> 2. Use this as a starting point to converge with SP, and save_lapw as 
> CONV_W_SP_NO_SOC (one can also restore_lapw in another directory and 
> start there)
> 3. Use this as a starting point to converge with SP and with SOC (and 
> save_lapw to have it for the future)
>
> I often start with step 3 right away, but I think for a really large 
> system this might be really inefficient.
>
> How does the program know to use the starting density from the 
> previous step?
> Does restore_lapw creates the necessary files when I transfer to the 
> new directory?
> Is -NI or some other setting in run_lapw important here?
>
> At the moment I am using an older cluster with many cores and use 
> k-parallel. Still didn't manage with MPI, but maybe it is not needed 
> for what I want because my klist file is typically 50-80 k-points, 
> depending on the symmetry of the system. I use the QTL program quite a 
> lot so having it parallellized would sometimes speed the things up a 
> bit for me.
>
> Best,
> Lukasz
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-- 
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Peter Blaha,  Inst. f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-158801165300
Email: peter.blaha at tuwien.ac.at
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