[Pw_forum] Energy variations in noncolin-constrain_total.in with OpenMP & MKL

[Nick Wilson]

> On 26 Jan 2016, at 20:02, Paolo Giannozzi <p.giannozzi at gmail.com> wrote:
> 
> 
> One should obtain the same numbers - within the errors due to roundoff, though -  in serial, OpenMP, MPI execution, and on different machines, and with different compilers and mathematical libraries.
> 
> ... actually, only at exact convergence, at least when using default wavefunction initialization: small differences come from different randomization of atomic wavefunctions. These however disappear as convergence is made tighter (but sometimes they don’t


Thanks Paolo & Stefano, that’s very useful information.

The convergence threshold was at 1.0e-9 and when I tightened it to 1.0e-12 it improved the agreement significantly.

Best regards,
Nick
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