Setting a High Force Constant for Constrain Option Causes Issues

grimme-lab / xtb

Semiempirical Extended Tight-Binding Program Package

https://xtb-docs.readthedocs.io/

GNU Lesser General Public License v3.0

567 stars 142 forks source link

Setting a High Force Constant for Constrain Option Causes Issues #936

Open sbembenek18 opened 8 months ago

sbembenek18 commented 8 months ago

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 commented 7 months ago

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 commented 7 months ago

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