[CPMD-list] Constraining Center of Mass

[Ari.P.Seitsonen at iki.fi]

Dear Luca,

  Yes, it seems that in the current version (I don't know about 3.4.3)
the 'FIX COM' only works with the optimisation of the geometry.
However you could remove the COM motion from the velocities easily
after the calculation of the new velocities (with call a to
'FIXCOM()'? It's not necessary to do this every iteration), or you
could fix one atom. Hopefully this helps you further.

    Greetings,

       apsi

>      I need to constraint the CofM in a MD simulation. These because,
> with nose thermostats for ions and wavefunctions swithched on, for a
> system I am studying there are huge drifts in the CofMass, that is
> absorbing a consistent amount of the total kinetik energy, so that the
> real temperature of the system is far from the target. It seems that the
> keyword FIX COM (reading the code) does work only during a geometry
> optimization, and not the MD run. Is that true (I am using version
> 3.4.3)?
> Is there a way to constraint the center of mass, better than restart
> every now and then to impose a new set of velocities?
> 
> Regards,
> Luca Ghiringhelli.

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