[Wien] proper k-points for Nd

[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 <
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>
> >Reply-To: A Mailing list for WIEN2k users <
> wien at zeus.theochem.tuwien.ac.at>
> >To: A Mailing list for WIEN2k users <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 ; Corrosion in 4D: MURI4D.numis.northwestern.edu
Partner of the CFW 100% program for gender equity, www.cfw.org/100-percent
Co-Editor, Acta Cryst A
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