[Wien] Three questions

Wed Sep 19 19:31:29 CEST 2018

> Could you describe the second symmetry in struct file:
>  -1 0 0 0.00000000
>   0-1 0 0.00000000
>   0 0 1 0.00000000
>         2   B   3
> 
> Is that generic for SOC?

This is an operation which trnsform x into -x,  into -y and leaves z 
unchanged. So obviously this is a 2-fold rotation (180 degrees) along 
the z direction.
I don't know what you mean by "generic for SOC" ??? For an arbitrary M 
direction, most likely nothing will survive except identity.

Forget "PRATT" (except sometimes for one cycle). For metals, bad 
convergence usually also means a need for a better k-mesh.

Sometimes some properties are very sensitive, so you need to check the 
convergence of this property.
Sometimes a property can depend on E-temp, in particular when very flat 
bands (high DOS) close to EF are present and it is a spin-polarized case.
If you want the T=0 solution, you have to use TETRA and a VERY GOOD 
k-mesh. Your results MUST be checked for k-convergence.

When you have transition metals (or even 4f elements) as atoms with the 
smallest RMT, RKMAX=7.5 is definitely too small for accurate solutions 
with fine details. Use at least 9. Of course, whne your smallest atom 
(RMT) is a light sp-element, RKMAX=7.5 might be fine.

> For a series of angles (say every 5 degrees) the results for same angles 
> are "off", one can see it clearly from plotting 2D sheets of bands, 
> since they e.g. exhibit Weyl points that "move around" when M direction 
> is changed.
> 
> What is strange is, that increasing the convergence criteria from -ec 
> 0.0001 -cc 0.001 to -ec 0.0001 -cc 0.0001 may lead to quite dramatic 
> changes, while keeping everything else intact.
> 
> I tried -fermit 0.004, that again leads to very different dispersions 
> for some bands. Now I am trying -fermit 0.00074 (10 meV). I am using 
> RKmax 7.5, that should be fine, but maybe I should increase to 9?
> 
> Perhaps there is some issue with the default mixer? Sometimes it takes 
> many iterations to converge for some M angles, while only few for other 
> M angles. I am now testing with the PRATT setting, maybe it will be more 
> consistent.
> 
> Maybe you could advice what else can be tried.
> 
> Best,
> Lukasz
> 
> 
> 
> 
> 
> 
> 
> 
> 
> On 9/10/2018 11:49 AM, Peter Blaha wrote:
>>
>>> 1. CHARGE CONVERGENCE: I know this has been discussed before, but it 
>>> seems it didn't change in Wien2k_18. Here is a typical example of the 
>>> charge convergence history of the last few iterations of FM+SOC 
>>> (ferromagnetic + spin orbit coupling) calculation:
>>>
>>> :ENERGY convergence:  0 0.0001 .0001320450000000
>>> :CHARGE convergence:  0 0.001 .0027578
>>> :ENERGY convergence:  1 0.0001 .0000497650000000
>>> :CHARGE convergence:  0 0.001 .0050904
>>> :ENERGY convergence:  1 0.0001 .0000557650000000
>>> :CHARGE convergence:  0 0.001 .0004672
>>> :ENERGY convergence:  1 0.0001 .0000220050000000
>>> :CHARGE convergence:  1 0.001 -.0001786
>>>
>>> Something strange happens with charge convergence, is this OK?
>>
>> This is ok.
>>
>>
>>> 2. LIMITS in inso and in1c files: in order to avoid large vector 
>>> files I am changing the energy limits in inso and in1c files for band 
>>> structure calculations. SCF is done with default inso and in1c files, 
>>> then I do save_lapw, then I edit case.inso and case.in1c files, and 
>>> then I do FM+SOC band structure calculation:
>>>
>>> #! /bin/bash
>>> x lapw1 -band -up -p
>>> x lapw1 -band -dn -p
>>> x lapwso -up -p
>>>
>>> I am using emin/emax -0.5 0.5 in both files (inso and in1c) without 
>>> changing anything else, then I have bands from limited energy range. 
>>> I just want to make sure that this procedure is fine.
>>
>> No, this is NOT ok. You must not change Emax in case.in1c !
>> If you do, your basis set for the spin-orbit step is limited and 
>> eigenvalues will change as compared to the scf calculation.
>> You can reduce emax in case.inso if you are not interested in the 
>> bands at higher energies.
>>
>>
>>> 3. FM+SOC convergence: I am doing FM+SOC calculations for different 
>>> in-plane magnetization M directions in a 2D Fe(001) ferromagnetic 
>>> layer. Actually an older Wien2k_14 version was not working well for 
>>> this, results for generic M directions were really strange. Wien2k_18 
>>> seems much better, however, when starting things from the scratch 
>>> (each M angle completely separate calculation) it seems that for some 
>>> M angles the result is off, as if it didn't actually properly 
>>> converge. I am using a fairly dense mesh for SCF (2000k, 25 25 3), 
>>> and -ec 0.0001 -cc 0.001.  Should I maybe try -fermit setting in 
>>> init_lapw, and what would be a reasonable value? Do I always need to 
>>> use instgen_lapw before init_lapw when starting a new case? Should I 
>>> perhaps do each next M angle on top of a previously converged M angle 
>>> (and save_lapw for each M angle)?
>>
>> Doing separate calculations for different directions may / may not 
>> yield correct results.
>> The proper (save) way is to use ONE case.struct file for all cases.
>> i) select all directions of magnetization first.
>> ii) Produce (using init_so) struct files, which are the same for all 
>> cases (do not change after init_so) and use this struct file for ALL 
>> (also non-so) calculations.
>> This works as:
>> a) generate normal struct file.
>> b) init -b -sp ....
>> c) init_so    with first direction, accept the generated structure
>> d) init_so    with second direction, accept ...
>> repeat this for all desired directions (or until you have a P1 
>> structure (only identity).
>>
>> e) with this setup (no new init_lapw !!!!) execute:
>>   runsp -ec ...      and save as   "non-so"
>>   runsp -so ...      and save as   "so-dir_2"
>>   restore non-so; edit case.inso and put the first direction in;
>>   runsp -so ...      and save as   "so-dir_1"
>>
>> In this way, you can also compare the force-theorem  (:SUM of first 
>> iteration (2 numbers !) with the scf solution.
>>
>>
>>
>>>
>>>
>>> Best,
>>> Lukasz
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>>
> 
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-- 
--------------------------------------------------------------------------
Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
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Email: blaha at theochem.tuwien.ac.at    WIEN2k: http://www.wien2k.at
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