[Pw_forum] Energy conservation in Verlet-MD?

Stefano de Gironcoli degironc at sissa.it
Thu Jun 24 16:05:43 CEST 2010

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

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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