total energy decrease, but KE and PE are conserved during MD simulation

Bikramjit Sharma bikram... at
Fri Sep 15 05:13:55 UTC 2017

Dear Thomas Kühne,

      Thank you very much for your reply. 

I have run CP2K for other bulk systems, where the total energy also 
fluctuates around an average value during equilibration in the NVT 
ensemble.  In case of clusters only, the equilibration in NVT ensemble 
shows the negative drift in total energy. That is why I am little unhappy 
with the gradual decrease in total energy of the system. Nevertheless, I 
have tried with time step of 0.25 fs and the thermostat is now applied in 
"GLOBAL" region (earlier it was MASSIVE). Till now it seems to have well 
behaved total energy fluctuation, although only longer run will tell the 
actual story.

Bikramjit Sharma 

On Friday, September 15, 2017 at 12:18:31 AM UTC+5:30, Bikramjit Sharma 
> Dear CP2K users,
> I am running MD simulations of some isolated ion-water clusters using 
> CP2K. I have first optimized the cluster in g09 and ensured it to be at 
> least a local minima. However, during equilibration, the total energy 
> continuously decreases while KE and PE shows well behaved fluctuations 
> after a few initial steps. I have run the equilibration for 10 ps and I 
> think that should suffice to converge the properties of the system. Even 
> though the total energy keeps on decreasing. I am attaching my input file 
> and the energy plots here. Any suggestion will be highly acknowledged. 
> Thanks in advance,
> Sincerely
> Bikramjit Sharma
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