The ABINIT Users Mailing List ( CLOSED )

[Michel Côté <michel.cote@umontreal.ca>]

Title: Re: [abinit-forum] For efficient atomic relaxation in many atoms system

Actually, 60 steps for 50 atoms is not so bad. You have 50*3 degrees of freedom and you get it relaxed in much less than that number. Remember that when relaxing a structure, the values of the forces need to be precise enough for the convergence, this means that you should use toldff for criteria and use a value less than 5d-5.

Michel


Le 04/04/07 08:31, « Anglade Pierre-Matthieu » <anglade@gmail.com> a écrit :

> Hi,
>
> Apparently there is no better value for ionmov at present. I don't
> know the reasons why this algorithm is supposed to be most efficient
> for system with few degrees of reedom either. This last statement
> seems surprising to me since Broyden method is a very good algorithm
> for local minimisation. If you really need it you might try to
> implement a preconditioner to your minimisation problem. This may be
> the only efficient improvement you can add to BFGS. It consist in
> adding an explicit hessian guess to the implicit hessian evalutaion
> done by BFGS.
>
> Regards
>
> PMA
>
> On 4/4/07, Chol-Jun Yu <yucj@ghi.rwth-aachen.de> wrote:
> > Dear users,
> >
> > I found that it could take much time (sometimes BFGS steps more than 60 in
> > order to arrive convergence, 5*10-5 Ha/Bohr) to relax the atomic positions if
> > the number of atoms is much larger more than 50, for example, for surface
> > supercell. I usually used the ionmove=2. Is it possible to reduce the BFGS
> > steps by using other values of "ionmov" parameter?
> >
> > With best wishes,
> >
> > Yu Chol Jun.
> >
> >


-- 
*************************************************************** 
  Michel Cote                          tel: +1 (514) 343-5628     
  Professeur agrégé                   fax: +1 (514) 343-2071               
  Département de physique 
  Université de Montréal 
  C.P. 6128, succ. Centre-ville 
  Montréal (Québec) H3C 3J7          Michel.Cote@umontreal.ca 
  Canada                   www.phys.umontreal.ca/~michel_cote 
***************************************************************