How to compute the pressure in hollow pillar

dear lammps members:
The ‘system volume’ in lammps is the volume of the box , not the volume of all atoms. So, when I compute the stress in
the hollow pillar,which’s atoms is not full in the box, is lammps come out a precise value of pressure? For example, is the " pxx " really the precise value of the normal stress of the hollow pillar in X direction ?
if it’s not precise, how can i correct it through lammps ?
Thanks in advance.

You’re asking a conceptual question, not a LAMMPS
question. The LAMMPS doc pages give the eqs
for what it computes. Explain what the equation is
for what you want to compute, if it is different. I don’t

think what you are asking is well-defined.