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[lammps-users] Fix NPT aniso stabilises at incorrect pressure
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[lammps-users] Fix NPT aniso stabilises at incorrect pressure


From: "Dzepina, Branislav" <b.dzepina15@...68...>
Date: Wed, 21 Jun 2017 09:13:39 +0000

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.

 

Cheers,

Brani