Newton's law

[reyhoon1998]

Hi,
Is there any way in HOOMD to turn off Newton’s second law? I want to implement motion without any external forces, where a rod moves in a prescribed way, so I need to disable Newtonian dynamics.
Thank you so much for your help.

[joaander]

All MD integration methods in HOOMD-blue operate on a subset of the entire system. Choose the filter argument to exclude the particles you wish to control explicitly. The Placing barriers in the simulation box tutorial demonstrates this technique.

[reyhoon1998]

Thank you so much. However, I'm trying to achieve motion without external forces by creating a 'reactionless drive' where I have a rod (consisting of 4 bonded particles) and a particle in front which is bonded to the rod. This front particle pulls on the rod (via one potential), but the rod doesn't pull back on it, violating Newton's 3rd law. Sorry, I mistakenly said 2nd law - when I checked the documentation you sent, I realized I was talking about a different Newton's law.
Also, in the documentation with barriers, the barriers don't move, but in my case everything needs to move.

[joaander]

Also, in the documentation with barriers, the barriers don't move, but in my case everything needs to move.

The implication was that you control explicitly the non-integrated particles using your own custom code, as we extensively discussed in #2167.