[lammps-users] fix rigid and fix npt

Hi, all,

It is said in the manual that all atoms in the system are re-scaled regardless of what atoms are in the ‘fix npt’. But I’m still not very sure how the atoms are re-scaled if fix rigid and fix npt are used together. Are the atoms in the rigid body re-scaled as a whole with their relative positions in the rigid body unchanged, or re-scaled individually with relative positions changed? If the latter is the answer, is there a way to rescale these rigid atoms as a whole?

Thank you

Fix npt rescales all the atoms, but then makes a call to fix rigid for it
to rescale the center-of-mass of the rigid body and reform the
rigid body correctly. So when the box size doubles, the rigid body
will not become twice as big, it will simply move to a new position
in the scaled box.