[lammps-users] NPT in a vacuum for a crystal surface with xy periodicity

We used "boundary p p s" command to define a surface in z-axis in the
simulation box. However, when we used "fix npt" command with "aniso
0.0 0.0 0.0 0.0 0.0 0.0 0.04 drag 0.2" and "aniso NULL NULL NULL NULL
0.0 0.0 0.04 drag 0.2" to simulate the vacuum, we got the following
error message; "ERROR: Cannot fix npt on a non-periodic dimension".
Is there another way to do an NPT simulation for a surface in a
vacuum? Thanks for any help.

   Best regards.

   Berk ONAT
   Informatics Institute
   Istanbul Technical University
   e-mail:[email protected]...

No, there's not in the current LAMMPS. I'm not clear what it would
mean to control the pressure/volume on a non-periodic dimension with a
free surface.


I used to simulate a free surface(or film) with a NVT ensemble, that keeps xy plane constatnt, while shrinks in the z axis.

BTW, I noticed a paper: Molecular dynamics results on the pressure tensor of polymer films( JCP, 113:4444(2000) ), that uses the anisotropy of the perpendicular and parallel components of the pressure tensor the surface tension of the system.