[Pw_forum] espresso3.0 different results in serial and paralel mode...

[Konstantin Kudin]

 Well, if the number of SCF iterations differ by so much, the
possibility that it is some kind of a bug and not just pure bad luck is
pretty high ...

 Could you post a) the progress of the total energies toward
convergence for both runs and b) the actual input file ?

 Also, it'd be nice if you could test the CVS version and see if this
behaviour is also there.

 Kosgtya
 

--- Cyrille Barreteau <cbarreteau at cea.fr> wrote:

> Ok so there is nothing to worry about.
> I was just a bit puzzled also by the fact that
> it took 14 iterations to converge in serial and
> 24 in parallel (for the wire).
> But maybe it was just bad luck..
> 
>   cyrille
> 
> 
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> 
> On Jeu 26 janvier 2006 14:42, Gerardo Ballabio a écrit :
> > On 01/26/2006 02:07:42 PM, Cyrille Barreteau wrote:
> >>   serial
> >>      the Fermi energy is    12.4997 ev
> >>
> >> !    total energy              =   -61.13842278 ryd
> >
> >>      band energy sum           =     6.08329685 ryd
> >
> >>   cluster
> >>      the Fermi energy is    12.4997 ev
> >>
> >> !    total energy              =   -61.13842278 ryd
> >
> >>      band energy sum           =     6.08329678 ryd
> >
> > I would not mind. It is quite normal for iterative methods to reach
> > convergence through different paths as soon as anything changes.
> > Between serial and parallel execution there are probably some
> > operations that aren't performed in the same order, and as the
> > numerical accuracy of computer numbers is finite, this can give
> > slightly different results.
> >
> > It is also normal that the total energy converges to a better
> > accuracy than the parts it is composed of. Thus if the convergence
> > threshold is 1e-8, you'll get 8-digit accuracy on the total energy,
> > but one or two less on other terms. It isn't a problem, but if you
> > mind, try changing the threshold to 1e-10 or 1e-12, I'm sure the
> > differences will go away (but it'll probably take a few more
> > iterations to converge).
> >
> > Gerardo
> >
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> 
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