Colvars:distanceZ, does the force generated by the spring act on both the "main" and "ref" atoms?

Hello,all. When using the Colvars module in LAMMPS, I would like to ask whether the “main” and “ref” atomic groups defined when using “distanceZ” are subjected to spring force defined by “harmonic”, or whether only the main atomic group is subjected to spring force?
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While a definitive answer should come from the COLVARS authors, it seems pretty intuitive to me that a colvar based on distance between two groups would exert an equal and opposite force between both groups, based on Newton’s first third law.

Isn’t that Newton’s third law?

The first two were retrenched in the big tech layoff. Redundancies with Lagrangian mechanics and all that, you know?

(Of course you’re right! That’s a huge brain fart on my part.)

You could say that you accidentally used a single bit unsigned integer instead of a two bit one, and the result just wrapped around.

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Thanks for your reply! So if I only want to force one group of atoms, I can only define the other group as dummy atom?

I guess? In general, simply don’t time-integrate your second group, and you should get the thing you want. Just make sure you read the disclaimer.

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Thanks a lot