Dear All
I am simulating a cluster with non periodic boundary condition on 3 directions.
using fix nvt to control the pressure and then obtaining surface energy.
the question is about pressure,when i used thermo_modify to monitor the pressure,i obtained high value of pressure.
but i think “boundary s s s” means the cluster is on vacuum.so the presssure should be near zero.
Best Regards
Malihe
Dear All
I am simulating a cluster with non periodic boundary condition on 3
directions.using fix nvt to control the pressure and then obtaining surface energy.
there is no "pressure" control with fix nvt.
the question is about pressure,when i used thermo_modify to monitor the
pressure,i obtained high value of pressure.but i think "boundary s s s" means the cluster is on vacuum.so the presssure
should be near zero.
the value that LAMMPS computes as pressure under non-periodic boundary
conditions has no meaning.
please see the formula, how pressure is computed here:
http://lammps.sandia.gov/doc/compute_pressure.html
under non-periodic boundaries, the volume is effectively infinity and
doesn't change. what LAMMPS uses as volume of the simulation cell is
truncated completely arbitrarily for technical and convenience
reasons. thus if you correct for this arbitrary truncation, the
pressure *must* be zero by definition, since any finite number divided
by infinity results in zero.
axel.