[gmx-users] how to make a rigid entity

[niaz poorgholami]

I would like to calculate the PMF between two nanotubes covered
with surfactants. for doing this, one nanotube have to hold fixedly and
another one have to move as rigid entity. for fixed nanotube I used
position restraints, however, I do not know how to make a nanotube a rigid
entity? I would be pleased if someone could help me.
        Thank you