Setting a High Force Constant for Constrain Option Causes Issues

[sbembenek18]

When using the constrain option via the .inp file, I find that having a very high force constant (force constant=100.0) results in the erratic movement of those atoms that are supposed to be constrained while the unconstrained ones do not move at all.

Thoughts on this?

[Albkat]

Hello, over-constraining in general could introduce numerical instabilities during optimization. Still, I cannot reproduce this behavior. Could you share your input and output data?

[sbembenek18]

I've attached the files for two constrained runs, (at 1, 100). For the latter, the system starts to erratically displace the atoms that are supposed to be constrained, while the unconstrained atoms essentially remain motionless. I'm able to view this by animating the xtbopt.log (via jmol).

Thanks for looking into this issue.

Constraint_Issue.tar.gz