The ABINIT Users Mailing List ( CLOSED )

["Josef W. Zwanziger" <jzwanzig@jzwanzig.org>]

I used ecut 15, pawecutdg 40, ecutsm 0.0 and 0.5. And, in accord with Matthieu's remarks, I find magnetic BCC iron to converge slower than nonmagnetic insulators and metals. What often happens for me is that convergence seems to proceed normally for some steps (say 20) then get worse again for awhile, then abrubtly get much better and complete. However, I don't find any dependence on ecutsm to the convergence rate.

Joe

 

Josef W. Zwanziger
Professor of Chemistry
Canada Research Chair in NMR Studies of Materials
Director, Atlantic Region Magnetic Resonance Centre
Department of Chemistry
Dalhousie University
6274 Coburg Road
Halifax, Nova Scotia B3H 4J3 Canada
tel: +1.902.494.1960
fax: +1.902.494.1310
web: http://jwz.chem.dal.ca
jzwanzig@jzwanzig.org,jzwanzig@dal.ca

---

From: matthieu verstraete <matthieu.jean.verstraete@gmail.com>
To: forum@abinit.org
Sent: Friday, December 12, 2008 8:27:24 PM
Subject: Re: [abinit-forum] ecutsm and electronic convergence

Hello,

I notice Emmanuel's pawecutdg is very low (22.5). Are you sure it is converged, and in particular that it is still converged once you add ecutsm (I think it is affected by ecutsm the same way normal ecut is - the contribution of those plane waves with energies in the last ecutsm Hartrees are smoothly cut off to 0). As it should be around, and sometimes higher than, 2*ecut, subtracting ecutsm=0.5 from it may change convergence. Try with pawecutdg 40 to see. Also, do all your runs converge to the same energy? You need a reference too, with higher ecut and pawecutdg=2*ecut. Joe - which values did you use?

On a side note, magnetic systems are often hard to converge, and can have multiple local minima, unlike normal DFT. Non-collinear magnetism is even worse.

Matthieu

On Fri, Dec 12, 2008 at 11:03 PM, Josef W. Zwanziger <jzwanzig@jzwanzig.org> wrote:

Hi, I can't repeat what you are finding. If I explicitly break the BCC symmetry of iron by straining the sample, it doesn't change the convergence with respect to the value of ecutsm at all. I have also used ecutsm to optimize cell geometries in lots of non-cubic cases, and never had a problem like what you are describing. I'm stuck. Maybe someone else can be more helpful?

Joe

 

Josef W. Zwanziger
Professor of Chemistry
Canada Research Chair in NMR Studies of Materials
Director, Atlantic Region Magnetic Resonance Centre
Department of Chemistry
Dalhousie University
6274 Coburg Road
Halifax, Nova Scotia B3H 4J3 Canada
tel: +1.902.494.1960
fax: +1.902.494.1310
web: http://jwz.chem.dal.ca
jzwanzig@jzwanzig.org,jzwanzig@dal.ca

---

From: Emmanuel Arras <emmanuel.arras@cea.fr>
To: forum@abinit.org

Sent: Friday, December 12, 2008 2:40:23 PM
Subject: Re: [abinit-forum] ecutsm and electronic convergence

Ok, I think found the problem. In fact, it happens when the box is non-isotropic :
Here are the plots of the electronic convergences ( deltaE(h) ) vs SCF steps for 4 calculations :
Fe-BCC_ecutsm_iso :  smearing = 0 and 1, on a cubic box (acell 3*2.9 angstrom)
Fe-BCC_ecutsm_aniso : smearing = 0 and 1, on a non-cubi box (acell 2*2.9 3.1 angstrom)
the output given is the one for non-cubic box and smearing = 1.
What do you think?


Emmanuel Arras a écrit :

I will try this on Fe BCC. Maybe it is linked with my pseudo, or my system (which is quite specific).
Thanks for your response. I'll keep you posted.

Emmanuel ARRAS

Josef W. Zwanziger a écrit :

This is odd. I've done lots and lots of PAW calc's, with ecutsm and without, on magnetic and non-magnetic systems, and have never observed anything like what you're describing. Can you post your input file?


 Josef W. Zwanziger
Professor of Chemistry
Canada Research Chair in NMR Studies of Materials
Director, Atlantic Region Magnetic Resonance Centre
Department of Chemistry
Dalhousie University
6274 Coburg Road

Halifax, Nova Scotia B3H 4J3 Canada
tel: +1.902.494.1960
fax: +1.902.494.1310
web: http://jwz.chem.dal.ca
jzwanzig@jzwanzig.org,jzwanzig@dal.ca



----- Original Message ----
  

From: Emmanuel Arras <emmanuel.arras@cea.fr>
To: forum@abinit.org
Sent: Thursday, December 11, 2008 1:27:40 PM
Subject: [abinit-forum] ecutsm and electronic convergence

Dear abinit users,
   I have observed that the use of ecutsm (typically 0.5 Ha for a cutoff 
of 10 Ha, ecut CV around e-2 eV/atom) makes it very difficult for abinit 
to achieve convergence : i.e. over 200 iterations to reach e-8 in toldfe 
(despite a steady slope), as compared to the 30 usually needed 
iterations. I am wondering where this comes from, and how to solve this 
issue.
  Note that I am using paw, and that my system is magnetic. It seems in 
fact that magnetism is hugely affected by this ecutsm : it takes much 
more time to reach final value (whereas magnetism is usualy very quick 
to converge). Also note that whatever the cutoff (up to 20 Ha, which is 
huge in paw), this problem appears.

Thanks for any advices.

Emmanuel ARRAS
    

--
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Dr. Matthieu Verstraete

European Theoretical Spectroscopy Facility (ETSF) 
Dpto. Fisica de Materiales, 
U. del Pais Vasco,            
Centro Joxe Mari Korta, Av. de Tolosa, 72,   Phone: +34-943018393
E-20018 Donostia-San Sebastian, Spain        Fax  : +34-943018390

Mail : matthieu.jean.verstraete@gmail.com
http://www-users.york.ac.uk/~mjv500