I would be very grateful for some newbie-level advice from a thermodynamics guru.
I ran NPT simulations on a particular system (in CP2K software) to get fluid densities for use in fluid dynamics applications. Before the lockdown, a colleague mentioned that it might be interesting to use the results for describing mixing in the system thermodynamically (the system is made up of two endmember compositions). I finally thought about it, but can't figure out if my NPT internal energy data are meaningful and don't want to bother my colleague, who has been sick. I would love advice.
I would like to know if I can simply sum my NPT ensemble-derived kinetic and potential energies to calculate internal energy. The reason I ask is that I came across a comment online where someone seemed to think the thermostat would interfere with the kinetic energy values.
I can't decide if this is true. I know that energy is not conserved for NPT simulations--that energy is either added or subtracted to maintain a constant temperature. However, it seems like that should be fine because I want the system to be at a particular temperature. I could run another set of simulations in a different ensemble. But that would mean a lot of extra time and computational resources, so I want to be really certain before diving in to doing more simulations.
With regard to energy not being conserved for NPT simulations, I'm wondering if it matters that my goal is to provide people with data on the thermodynamics of mixing in the system. In other words, for the data to be useful, I need to be compare internal energies from distinct simulations run at the same pressure and temperature, but different endmember fractions (compositions)--one internal energy value by itself probably won't be useful. I'm not sure if I'm being clear here... The bottom line is that I can't figure out if it would be like comparing apples and oranges to compare internal energy values from different NPT simulations (and therefore cannot use my existing results to describe the thermodynamics of this system).
I have searched online for information on this, but probably don't know enough to be familiar with useful search terms. If anyone has any hints on how to think this through, I'd be very appreciative. Thank you.