Re: [Wien] proper k-points for Nd

[Laurence Marks]

"Honest disagreement is often a good sign of progress" -- Mahatma Ghandi

I am not offended that Peter does not agree with my view about noise.😀

_
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

On Sun, Jan 20, 2019, 12:01 Peter Blaha  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 1 k-points for every metallic spd-element
> and test it with 5 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 t...@theochem.tuwien.ac.at
> >   > > wrote:
> >
> > Hi,
> >
> > If not too expensive, you could try more k-points (2 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  > >
> >  >Reply-To: A Mailing list for WIEN2k users
> >  > >
> >  >To: A Mailing list for WIEN2k users
> >  > >
> >  >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 small

Re: [Wien] Spin-polarized DOS for dopants in non-magnetic materials

[Lyudmila Dobysheva]

18.01.2019 12:33, Marcelo Barbosa :

I’m calculating the DOS for dopants in semiconductors to get the corresponding 
impurity bands.
I’m dealing with non-magnetic materials and non-magnetic dopants, so I would 
assume that no spin-polarization was needed.
However, in some cases when substituting an atom for a dopant with different 
valence number, the DOS reveals an impurity band with different contributions 
from spin-up and spin-down due to the extra/missing electron. Also, the energy 
difference from the valence band maximum to the impurity band changes from a 
non spin-polarized calculation to a spin-polarized calculation.


An example: Cu and oxygen are nonmagnetic, but some Cu oxide is magnetic 
(AFM). So, your case is not surprising for me.



My question then is: should I consider the spin-polarized results every time 
the spin-up and spin-down contributions are different? Or is there any good 
argument to choose the non spin-polarized calculation instead?


IMHO, you should use the spin-polarized results. Though, this depends on 
what you are doing...


Best wishes
Lyudmila Dobysheva
--
Physics-Techn.Institute,
Udmurt Federal Research Center, Ural Br. of Rus.Ac.Sci.
426000 Izhevsk Kirov str. 132
Russia
---
Tel. +7 (34I2)43-24-59 (office), +7 (9I2)OI9-795O (home)
Skype: lyuka18 (office), lyuka17 (home)
E-mail: lyuk...@mail.ru (office), lyuk...@gmail.com (home)
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