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

[Gerardo Ballabio]

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