[lammps-users] physical interpretation of sign on pressure output

I am trying to set up an NVE simulation near a particular compressive hydrostatic stress - and have been confused by the thermo output (I think) for pressure in my system. I assume that a negative sign in the pressure indicates a net tensile hydrostatic stress in the system. Is that correct?



David E. Farrell

Graduate Student

Mechanical Engineering

Northwestern University

email: [email protected]…435…


A negative sign on the pressure means that the system wants to
contract. You could think of this as if the sample were in a tensile
test and the atoms were being pulled outward by an externally-applied
force (the force that maintains your box volume as constant in your
NVE ensemble). The interatomic forces would resist that
externally-applied expansive force and try to contract the system,
which would be evidenced in the NVE ensemble as a negative hydrostatic
pressure. If the box volume were allowed to relax (NPT ensemble with
P=0), the box would shrink until P=0.


Thanks for the info Paul,