[Pw_forum] espresso3.0 different results in serial andparalelle mode...

[Cyrille Barreteau]

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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