how to simulate a isentropic expansion process

Hello Sir,
I am trying to simulate a isentropic expansion process using lammps (the expansion of gaseous products after detonation). But I searched the manual and can’t find an ensemble to do the mission. Could you provide any suggestion on how to simulate a isentropic expansion process?
Guangyu Wang

You will have to use fix nve and let your system expand from the free surface, which means the free surface has a “s” or “m” boundary.

Make sure no reactions occur and no heat is exchanged (meaning no thermostat), then you have an isentropic process.


Thanks for reply. I am using lammps with ReaxFF potential function. So I guess there will be some reaction during the process (It happens in reality). But I will try your method.
Guangyu Wang

Then you will not have an isentropic process. Reversible and adiabatic processes rarely exist in reality. :slight_smile:


Maybe I Diverge…But from the first law of thermodynamics E = TdS - PdV , if you can make all the total energy be converted into mechanical work i.e Etotal = PdV, then TdS = 0, which means you have constant entropy and thus an isentropic process or at least quasi-isentropic …In Theory I believe an Isentropic process can do exist in environments where you compress or expand really quickly , and thus there is not enough time for heat transfer intro the environment

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