[Pw_forum] Energy conservation in Verlet-MD?

[Norbert Nemec]

Thanks, Stefano -- inspired by your information I tried various versions of PWSCF and finally found out that a uncommitted patch that I had believed to be completely independent actually slightly messed up the forces during the SCF loop.

Will not be easy to fix the problem, but at least I have identified it now...




-------- Original-Nachricht --------
> Datum: Thu, 24 Jun 2010 16:05:43 +0200
> Von: Stefano de Gironcoli <degironc at sissa.it>
> An: PWSCF Forum <pw_forum at pwscf.org>
> Betreff: Re: [Pw_forum] Energy conservation in Verlet-MD?

> with your input on my computer the "constant" is oscillating within a 
> range of the order of 3e-6 .
> the potential energy varies on a scale that is 1000 times larger
> stefano
> 
> Norbert Nemec wrote:
> > Hi there,
> >
> > I am trying a very simple MD calculation (optical phonon mode of
> Silicon, similar to the original Car-Parinello paper). I am surprised that the
> total energy is not constant but oscillates with about 10% of the amplitude of
> the potential energy.
> >
> > This oscillation is *independent* of the MD time step. Furthermore it
> did not change with the k-grid, the energy cutoff, the functional or the
> pseudopotentials.
> >
> > Attached is one of the input files that I used.
> >
> > Does anyone know what might cause this behavior?
> >
> > Greetings,
> > Norbert
> >   
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