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.