[Wien] proper k-points for Nd
Peter Blaha
pblaha at theochem.tuwien.ac.at
Sun Jan 20 19:01:33 CET 2019
I disagree with Lauries point: Eventually I want to do even an
"unphysical" calculation, of course it might be you have to pay a price
for it, because this unphysical model as eg. a spike in the DOS at EF.
And mixer should lead to convergence, but sometimes has problems
(Lauries mixer is still one of the big advantages of WIEN2k. I know
other codes, which would not be able to converge a 5f system at all).
In any case, put a HDLO (5f) and increase LVNS=6 first.
Most importantly: why are you starting from scratch when doing the
k-mesh tests. This is very error prone and in particular burns cpu-hours
completely unnecessarily.
One of my main "advises" is always: do an init_lapw only ONCE ! (except
you have to change spheres).
You will get much better internal convergence when you continue using
the previous calculation:
loop:
runsp ....
save XXX-k-points
x kgen (increase the mesh always at least by a factor of 2 (maybe even 4).
goto loop
I'm not so much surprised about the k-mesh for a magnetic 5d-element
calculation. I start with 10000 k-points for every metallic spd-element
and test it with 50000 k. You may need 100 000 or even more. (optics for
fcc Al is not fully converged with 1 000 000 k-points !). It does not
cost much cpu, since you should start with a nearly converged calculation.
Your :DIS is still quite large, try to bring it below 0.0001
You can try TEMPS 0.002 as Laurence advised. This will most likely
improve convergence, but most likely also reduce MMT a little bit, which
is ok when you compare with room temp experiments, but not for 4k
measurements ...
Am 20.01.2019 um 17:50 schrieb Laurence Marks:
> Sorry Fabien, I am dubious that k-points is the issue, I suspect a bad
> model.
>
> Let me explain, repeating some things I have said before or are in the
> mixer notes albeit perhaps buried.
>
> An "easy" assumption that many people make is that dft problems are well
> posed, so have "simple" fixed-point solutions. In fact this is not true.
> In reality dft problems have stacks of numerical issues which leads to
> "noise". You can think about this in terms of finding the minimum of
> "F(x) = x*x + Constant*Noise(x)" where Noise(x) is some randomly
> generated noise. The larger Constant is, the larger the deviation is
> from x=0 of the apparent minimum. Averaging over more k-points may
> reduce Constant, but often in my experience does relatively little.
>
> A symptom of noise is poor convergence -- which is clearly what is
> occurring here.
>
> If you improve the convergence rate you will reduce the noise. Some
> suggestions:
>
> 1) Use HDLO and reduce RMT
> 2) Reduce RMT and use HDLO
> 3) Larger LM (e.g. 8)
> 4) Larger gmax in case.in2 (e.g. 16)
> 5) Use TEMPS 0.0018 (room temperature)
> 6) Peter's suggestions
>
> On Sun, Jan 20, 2019 at 10:27 AM tran at theochem.tuwien.ac.at
> <mailto:tran at theochem.tuwien.ac.at> <tran at theochem.tuwien.ac.at
> <mailto:tran at theochem.tuwien.ac.at>> wrote:
>
> Hi,
>
> If not too expensive, you could try more k-points (20000 and 25000)
> to see if the fluctuations persist.
>
> Questions: how many atoms in the unit cell? Are you optimizing the
> position of atoms?
>
> F. Tran
>
> On Sunday 2019-01-20 17:17, Victor Zenou wrote:
>
> >Date: Sun, 20 Jan 2019 17:17:55
> >From: Victor Zenou <zanov at post.bgu.ac.il
> <mailto:zanov at post.bgu.ac.il>>
> >Reply-To: A Mailing list for WIEN2k users
> <wien at zeus.theochem.tuwien.ac.at
> <mailto:wien at zeus.theochem.tuwien.ac.at>>
> >To: A Mailing list for WIEN2k users
> <wien at zeus.theochem.tuwien.ac.at
> <mailto:wien at zeus.theochem.tuwien.ac.at>>
> >Subject: Re: [Wien] proper k-points for Nd
> >
> >Dear Peter, LDM and wien2k users
> >I did some more calculation with energy and CHARGE convergence
> criteria
> >equal to 10^-4 Ryd and 10^-3, respectively. The energy usually
> converged to
> >1*10-5 or even 1*10^-6. Still I get energy fluctuation up to
> 4*10-2 Ryd
> >(please see below)
> >I didn't check AFM yet, but this is not the point. The point is to get
> >"stable" calculation for optimal k-points.
> >I have to say that for each calculation I totally aresed all file
> except
> >case.struc.
> >Also I used all defaults as well as gmax=12, also
> rmt(min)*kmax=8.5, for all
> >calculations.
> >I can repeat all calculation with smaller RMT, such as 2.5, or to
> check
> >HDLO.
> >I think I will start with smaller RMT. Any comments / suggestions?
> >Victor
> >
> >K-pointsIBZ E [Ryd], 10-4 CHARGE convergence CHARGE DISTANCE MMTOT
> >3000 208 -77040.50516761 -.000504 0.000825 16.00318
> >5000 280 -77040.48748499 -.000544 0.000758 16.68523
> >7500 455 -77040.51668342 -.000862 0.000183 16.62547
> >10000 540 -77040.48747210 -.000817 0.000499 16.67544
> >15000 840 -77040.46976815 -.000216 0.001362 16.64536
> >
> >
> >
>
>
>
> --
> Professor Laurence Marks
> "Research is to see what everybody else has seen, and to think what
> nobody else has thought", Albert Szent-Gyorgi
> www.numis.northwestern.edu <http://www.numis.northwestern.edu> ;
> Corrosion in 4D: MURI4D.numis.northwestern.edu
> <http://MURI4D.numis.northwestern.edu>
> Partner of the CFW 100% program for gender equity,
> www.cfw.org/100-percent <http://www.cfw.org/100-percent>
> Co-Editor, Acta Cryst A
>
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
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