[Wien] proper k-points for Nd

[tran at theochem.tuwien.ac.at]

Ok, let's see. Besides this, f-systems are also problematic
because of multiple local minima with similar energies.

On Sunday 2019-01-20 17:50, Laurence Marks wrote:

>Date: Sun, 20 Jan 2019 17:50:21
>From: Laurence Marks <L-marks at northwestern.edu>
>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
>
>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.eduPartner of the CFW 100% program for gender
>equity, www.cfw.org/100-percent
>Co-Editor, Acta Cryst A
>
>