redefine region

I want to simulate a cylinder shape. I first use the read_data to get a cubic. Then cut it to get the cylinder box. However the simulation box is still the cubic box. How can i get the cylinder box as the simulation box.

region all block 0 200 0 100 0 100
region 2 cylinder x 50 50 50 0 200

read_data data_3.2_20x10x10
group 1 region all
group 2 region 2
group 3 subtract 1 2

delete_atoms group 3


The simulation “box” in LAMMPS is always a box, though it
can be tilted (see triclinic docs). However the atoms don’t
have to fill the box. And there can be walls or various shapes
to constrain the atoms, e.g. to a cylinder. See fix wall/region
for example.