"Fix rigid" problem

Dear all

I tried to use fix rigid command in order to have a solid Graphene sheet while the movement of this sheet in one direction is free and in two other directions are not, i push this Graphene via water molecules and i want to calculate the interaction force between this sheet and neighbor water molecules. the problem is that using fix rigid for this sheet unfortunately results in torque and angular motion of this sheet while it supposed to move just in one direction.
Any help would be appreciated.

Best Regards,
Mahdi

How are you using the fix rigid command and how are you moving the graphene sheet? A rigid body can move and rotate freely – the graphene sheet is not supposed to just move in only one direction.

Also check out the Note from fix rigid doc page, “These fixes are overkill if you simply want to hold a collection of atoms stationary or have them move with a constant velocity. A simpler way to hold atoms stationary is to not include those atoms in your time integration fix. E.g. use “fix 1 mobile nve” instead of “fix 1 all nve”, where “mobile” is the group of atoms that you want to move. You can move atoms with a constant velocity by assigning them an initial velocity (via the velocity command), setting the force on them to 0.0 (via the fix setforce command), and integrating them as usual (e.g. via the fix nvecommand).” It seems to me you can use the above method instead.