[lammps-users] about periodic boundary condition

Hi,
In my simulaition,there are two problem.
(1)I want to do that in my input file:first,i use NPT with the P P P boundary condition to control the temperature and pressure,after that, i use NVE with the P P fs. As far as I know,once giving out the boundary condition, Don’t allow to chang it in the same input file.How can i do it ?
(2)In the simulation of cutting, I want to use periodic boundary (p p p) condition to the substrate,while free boundary condition to the cutting tool,how can i set it ?

best wishes,

Comments below.

Steve

2010/10/14 黄德明 <[email protected]>:

Hi,
  In my simulaition,there are two problem.
(1)I want to do that in my input file:first,i use NPT with the P P P
boundary condition to control the temperature and pressure,after that, i use
NVE with the P P fs. As far as I know,once giving out the boundary
condition, Don't allow to chang it in the same input file.How can i do it ?

You can't do it in one script. You can write out a restart file from
the periodic simluation, convert it to a data file, then read that into
a new script that sets the BC to be non-periodic. You should be careful
to define the box dimensions in the new data file to be consistent with
the new BC.

(2)In the simulation of cutting, I want to use periodic boundary (p p p)
condition to the substrate,while free boundary condition to the cutting
tool,how can i set it ?

Boundaries (periodic or not) are global settings, for the entire simulation
box. If the substrate is 3d periodic, then it is of infinite extent. What
does it mean to impose a cutting tool on the substrate from outside infinity?