Constraints are violated

Problem: constraints are violated: coordinates that were specified as frozen turn out to change during the optimization or coordinates that should remain the same start to differ after a few geometry update cycles.

Possible cause: there is an internal conflict between different demands, usually: symmetry versus constraints. The problem arises easily when a constrained optimization is requested for a molecule with some symmetry while the coordinates were defined with a Z-matrix structure that does not properly reflect the symmetry. Usually the deviations from the requested constraints are small. If they are really large, there might be a bug and you should contact an adf representative.

Cure: redefine the Z-matrix and/or use Cartesian optimization (if the constraints are expressible in Cartesians).