Question about restraining the center of mass

[Lee-Ping Wang]

Hi there,

If I wanted to restrain the center of mass of a molecule to a particular position (without restraining the individual atoms), should I use the CustomCentroidBondForce? I could create a fictitious particle with no mass and no other interactions so that it stays at a prescribed position, and that would be my group 2.

While this force seems to be intended to apply forces to the centers of masses of two or more groups, I couldn't find another Custom Force that would work for an individual group. Let me know if I missed something.

Thanks,

- Lee-Ping

[Peter Eastman]

CustomCentroidBondForce will happily let you define a "bond" based on only one group. For example, if you set your energy to "(x1-5)^2+(y1-2)^2+(z1-3)^2", that will restrain the center of mass to (5, 2, 3).

Peter

[Lee-Ping Wang]

Thanks a lot. That seems a lot simpler than creating a fictitious atom.