NVT and NPT of a two phase system

Dear all

I have a fluid-fluid system. after equilibration in NVT and NPT ensemble, both temperature and pressure are in the desired value. However, the parameters are different in the liquids.

I have done 2ns NVT and 2ns NPT to equilibrate the system.

I would appreciate if you let me your advice to get equal temperatures and pressures for the fluids.

Generally, if you have a two phase fluid-fluid system, any type of molecular dynamics will naturally bring the two phases into thermodynamic equilibrium, meaning the average temperature, the average pressure, and even the chemical potentials of the species will be the same in both phases. Verifying this is tricky, because the spatial locations of the phases may be changing over time. One simple test is to calculate the per-atom kinetic energy and per-atom stress summed over groups of atoms corresponding to the two phases. If you are using specialized methods such as SHAKE, then extra care must be taken to ensure that temperature and pressure are defined in a consistent way.