Hello everyone, I’m seeking guidance on calculating the phase fraction in a multicomponent system. Currently, I’m simulating a mixture of various substances under different pressures. I’m interested in understanding how the phase fraction (mass or volumetric fraction of gas and liquid) behaves with the variation in the system’s pressure. Therefore, I’d like to inquire about the best approach to perform this analysis.

Are there any LAMMPS commands available or recommended post-processing programs that could help me in this analysis? I appreciate any guidance or suggestions you may offer.

You can take a look at `compute orientorder/atom`

and `compute coord/atom`

.

As for post-processing software, you can find some here: Pre/Post Processing Tools for use with LAMMPS

Please look more generally for “phase coexistence methods” – and be aware that you face a fundamental constraint due to finite size effects in molecular dynamics.

Thank you both for your suggestions. I will look into it.

I would also like to know your opinion on enabling gravity in my simulation and performing post-processing on the system’s dump file to visually determine the volume percentage occupied by each phase. Would this approach be correct?

I suggest you perform the exercise to compute the magnitude of the gravitational force for the particles in your system and compare it with the magnitude of the forces from particle-particle interactions. Then you should be able to answer your question by yourself *and* have learned a useful skill.