Dear Lammps users,
I am encountering some strange behaviour regarding an NPT fix.
I am trying to simulate a box of ~54,000 Fe atoms at high pressure (7.7GPa) and temperature which are described using a MEAM potential (Phys. Rev. B 89, 094102).
I run the simulation for 200k timesteps with periodic boundaries in all directions.
If I use the fix:
fix 2 all npt temp 1860 1860 0.1 iso 77000 77000 1
the pressure stabilises within 2000 timesteps to the correct value.
However, If I try applying the same pressure only in the x direction:
fix 2 all npt temp 1860 1860 0.1 x 77000 77000 1
the pressure consistently stabilizes at ~10GPa throughout the entirety of the run.
A search through the forums brings up a user experiencing exactly the same problem (http://lammps.sandia.gov/threads/msg66409.html)
. The problem in their thread
it would seem was the core-shell package.
Could I have a similar problem with the MEAM potential? Or is there something I am misunderstanding.
Any advice would be greatly appreciated.