[Pw_forum] Problem in energy conservation in NVE MD using cp.x

[SAKUMA Hiroshi]

Dear Nicola,

Thanks for your kind explanation.
I will use the working version from the cvs and the new release of the code.

Best regards,

hiroshi

- 
Department of Earth & Planetary Sciences
Graduate School of Science & Engineering
Tokyo Institute of Technology
2-12-1 Ookayama Meguro-ku Tokyo 1528551
Kawamura Lab.
Tel: +81-3-5734-2617



Nicola wrote:

>Dear Hiroshi,


>thanks again for your observations - it turns out that in recent times 
>(years) a small modification had arisen in the way the center of mass
>is treated that gave rise (in the very exotic case that you have been
>looking at) to the observed behavior. Roberto Car and his group 
>(Federico Zipoli and Zhaofeng Li) has also noticed this a few months
>ago, but it has percolated back into the code just now.

>You can download the working version from the cvs, with these two >commands:

>cvs -d :pserver:anonymous at scm.qe-forge.org <http://www.democritos.it/mailman/listinfo/pw_forum>:/cvsroot/q-e login
>cvs -d :pserver:anonymous at scm.qe-forge.org <http://www.democritos.it/mailman/listinfo/pw_forum>:/cvsroot/q-e checkout >espresso

>or wait for a few days for the new release of the code, coinciding
>with the Santa Barbara school.

>If you apply it to your example, you'll notice that the constant
>of motion of the CP lagrangian is perfectly conserved, the physical
>constant of motion is very well conserved (as it should be), and also
>that after a fraction of a ps the water molecule will take up some 

>kinetic energy (average around 10K, i.e. osciallting between 0 and 20K)
>due to the transfer of momentum between the fictitious system and the
>physical one. This is normal, and the relatively large amount is due to
>this very unusual case, using on top a lot of plane waves. It would be 
>negligible in any large system.

>All the best,

>			nicola