[CP2K-user] Internal energy from a CP2K NPT simulation?

Ant ant... at gmail.com
Wed Aug 12 11:49:03 UTC 2020

I am a relative newbie and would be grateful if someone would please 
confirm whether that my understanding is correct with regard to calculating 
internal energy via CP2K NPT simulation.

For an NPT simulation, I know that the "conserved quantity" (column 6, 
.ener file) for an NPT simulation is not internal/total energy, but the 
energy of the system + the energy of the thermostat + the energy of the 
barostat.  However, I plan to calculate the internal energy by summing the 
potential and kinetic energies (columns 3 and 5, .ener file).  

I have already run simulations with this aim in mind, but came across a 
couple of forum posts that have made me a little nervous that the situation 
may not be as straightforward as I anticipated.  If anyone knows whether 
there is a problem with my plan, I would be grateful for a heads-up.  Thank 

(I have read that NPT simulation is not preferred for calculating the 
internal energy because small fluctuations in volume can lead to large 
variations in the internal energy.  It is convenient to run NPT simulations 
in my particular situation and I plan to run subsequent NVT simulations to 
find out if there is a significant difference.) 
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