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["Anglade Pierre-Matthieu" <anglade@gmail.com>]

Usually forces are much less converged than total energy on a scf
cycle. On small systems you need a convergence better than 10^-12 on
Et to get 10^-5 on forces  (On large system the ratio decreases but
you must increase nnsclo and nline to get a real convergence). 
altough I don't know exactly I'd say that you should expect exactly
the same behavior with respect to eCut that is at least a few order of
magnitude of difference towards absolute convergence between total
energy and forces.


On 3/29/06, Michel Côté <michel.cote@umontreal.ca> wrote:
>
> I do not understand your question very well. Toldff converge the largest
> force. If you have convergence up to 10-5 (5 digits), then it is normal that
> forces on atom that are smaller still change with increasing the cutoff. In
> other words, it is not the number of significant digit that is converged but
> the absolute number.
>
> Michel
>
>
> Le 29/03/06 10:41, «Nuno Galamba» <ngalamba@cii.fc.ul.pt> a écrit:
>
> > Dear Abinit users
> >
> > I have a simple question regarding the choice of ecut for an arbitrary 
> > system.
> >
> >  By doing a calculation for different values of ecut (say,
> > 10,15,20,25,30,35,40,45,50 Hartrees) for a given value of toldff (say 10-4
> > Ha/Bohr) one can  observe a plateau at which energy converges to.
> >
> > Now the question is, say the energy is converged for ecut=30 Ha (meaning 
> > it
> > does not change up to the first 5 digits), in principle the 
> > Hellmann-Feynman
> > forces on every particle of the system should be converged too.
> >
> > I am not quite sure this is the case. I observe that the force on the
> > particles of the system are not the same. These are of the order of 10-6
> > Ha/Bohr. Souldn't one expect some kind of convergence behavior for the 
> > force
> > on every particle when increasing systematically the number of plane waves
> > for a given calculation?
> >
> > Thanks in advance
> >
>
>
> --
> ***************************************************************
>   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
> ***************************************************************
>
>
>
>


--
Pierre-Matthieu Anglade