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

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
> 


-- 
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  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
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