[Pw_forum] Different convergence behavior in non-collinear SO calculation

[Paolo Giannozzi]

On Fri, 2014-10-10 at 11:42 +0200, H. Lee wrote:

> At least to me, this difference seems strange.

I have spent many hours tracking mysterious bugs that
turned out to be due to different processors yielding
different results ON EXACTLY THE SAME OPERATIONS ON THE
SAME DATA. Can you see why I do not find such differences 
so strange? :-) 

Paolo

> Regards.
> 
> 
> H. Lee
> 
> On Thu, Oct 9, 2014 at 10:02 PM, Paolo Giannozzi
> <paolo.giannozzi at uniud.it> wrote:
>         On Thu, 2014-10-09 at 20:29 +0200, H. Lee wrote:
>         
>         > Is this just an inevitable numerical noise?
>         
>         very likely. Some numerical noise is always there, it
>         is usually almost invisible, especially at scf convergence.
>         In some known cases of special sensitivity to truncation
>         and roundoff errors: noncolinear, spin-orbit, DFT+U, it
>         is more visible while self-consistency is reached. No
>         easy solution is known (to me at least)
>         
>         
>         P.
>         
>         --
>         Paolo Giannozzi, Dept. Chemistry&Physics&Environment,
>         Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
>         Phone +39-0432-558216, fax +39-0432-558222
>         
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-- 
 Paolo Giannozzi, Dept. Chemistry&Physics&Environment, 
 Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
 Phone +39-0432-558216, fax +39-0432-558222