“Hello, I am using LAMMPS to calculate the pressure of a system with fixed boundaries in all directions, containing a collection of active Brownian particles. I have printed the global pressure using thermo_style, but I am not observing any differences with varying activity strength of ABPs. Could you help me understand why this is happening?”
Please note that the “global” pressure in the thermo output is computed by an instance of the “compute pressure” command which is suitable for point particles, but has to be replaced for extended particles.
Please also note that with fixed boundaries you have an open system and for that global pressure is an ill defined property, since your volume is in essence infinite and thus your pressure must be zero. LAMMPS uses the box boundaries to determine the volume required to obtain the pressure from the collected virial, but those are arbitrary for open systems.
Thank you for your reply. Can you help me find the pressure on the walls at the edges of the fixed boundary?
That is your area of research not mine. Ask your adviser. That is the person that is supposed to advise you on your research, not me.