command to reorient H atom in a circle with fixed angle and OH bond

Dear Lammps User.

I am modeling the system which contains fully hydroxylated silica.
The Si and O atoms are fixed positions but the H atoms on the surface are able to move with fixed bond lengths and bond angles;each H atom can reorient in a circle.Such circular motion occurs in a plane parallel to the plate at a particular distance away from the O-atom plane of the Si-O-H groups.

I would use the command of “fix” to implement the Si and O atoms.
But I have no idea which command should applied to H atom to realize the reorient with fixed bond lengths and bond angles.
Does anyone who has any suggestion about this?

Thank you very much

All the best


fix bond/angle situations are a bit tricky to implement in MD (unlike in MC) simulations. such fixed relative geometries can be achieved with fixes in the RIGID or POEMS packages. there are many options and they all have different limitations and restrictions and may need adjustments to the input topology to work.