Region prism parameters

Hello users,

I have been trying to figure out how one chooses the parameters (edge vectors) for a region which is a prism?

The system that I am working on is graphane that has 8 atoms as it’s unit cell and I need to calculate the phonon dispersion curves using a 3rd party tool (phonolammps) for which I would need to have these edge vectors.

These phonon calculations are done for a 3 x 3 x 1 supercell. I am assuming that the edge vectors would have to fixed based on the size of the supercell.

please see: