[CP2K-user] Can I calculate the internal energy from NPT simulations or does the thermostat complicate things?
ant... at gmail.com
Thu Aug 13 06:26:20 UTC 2020
I would be very grateful if someone could help me out with what is probably
a newbie question. I have been unable to find the answer in text books or
I have existing NPT simulation results that I used to calculate density.
My question is, can I also use them to calculate the internal energy?
I know that for an NPT simulation, the "conserved quantity" (column 6 of
the .ener file) is *not* internal/total energy. It is the energy of the
system + the energy of the thermostat + the energy of the barostat.
However, is it a reasonable approach to calculate the internal energy by
summing the potential and kinetic energies (columns 3 and 5, .ener file)?
Or does the added energy from the thermostat somehow mess things up?
I found a paper where someone first ran CP2K NPT simulations and then used
the cell volumes to run NVT simulations to get the internal energy (I
assume because the fluctuations in V would be quite large for NPT and might
lead to error in internal energy--my internal energy averages from my NPT
simulations seem quite stable though). So someone has used a non-NVE
approach. However, I have a niggling feeling that the thermostat might be
doing something I don't understand. Thank you.
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