[lammps-users] Why is there a negative sign in "compute stress/atom" but not in "compute pressure"

I notice the words "Note that as defined in the formula, per-atom stress is the negative of the per-atom pressure tensor. ", but why does the expression need a negative sign?
Shouldn’t stress tensor be the same as per-atom pressure tensor?


Because those are the way LAMMPS and other codes and texts
define the 2 quantities.