Hi Shihai,
Here are my thoughts… Hope this helps.
- Create a cylindrical lattice of radius R
- Create a new cylinder region with radius R-r. (this till be your actual hollow radius in which the atoms will try to move).
- Delete atoms in this new region. You will get the hollow cylinder…
- Create the group of the remaing atoms in the cylindrical shell and use zero velocity and setforce zero to keep them fix… or dont include them in the fix.
- Now you can incorporate whatever you want within the hollow cylindrical region.
- In addition, for the interactions of atoms with the wall (this is a fictitious wall, thought, not 100% smooth), you could use either LJ potential or soft repulsive potential.
Vikas