[lammps-users] [Help] About group and add radial force

Hi, everyone

I am Jervis. I am new to LAMMPS.

I want to add radial forces to one dimensional nanowires (carbon nanotubes) to simulate high-pressure properties, but the problem is

(1) how to group the surface atoms especially when the wire’s shape is not a box (e.g. a hexangular prism). As far as I know, there is no direct way to group the surface atoms in LAMMPS.

(2) how to adjust grouping atoms list when the structure of the system changed, i.e, during simulaition, one surface atom may become an inner one, thus the group list should change.

(3) how to add radial forces to the grouping atoms. Although the fix addforce command can do the similar thing, but it can only add a constant force indepent of atomic coordination.

Can anyone give me a better way to implement the idear than editing the source codes of LAMMPS? Or, if changing the source codes, is there any suggestions?

Write a fix, e.g. fix radial/crush. It can loop over the
atoms and do all the things you list.