Geometry Constraints and Fixing Coordinates of MM atoms

Constraints can be applied to coordinates in the same way they are done with a standard ADF run (i.e. most commonly through the GEOVAR key block). There are no limitations to applying geometry constraints to QM or LI atoms, however, there exist some limitations to applying geometry constraints to MM atoms, particularly when using a Z-matrix.

When a geometry optimization is performed in Cartesian coordinates there is almost no limitation to applying constraints to MM atoms. One important exception is that linear transit constraints can not involve MM atoms. At the moment constraints cannot be applied to the coordinates that define the position of the MM atoms when internal (ZMAT) coordinates are used. Note that constraints still can be applied to the coordinates of the QM atoms, but just not to the MM atoms.

Symmetry constraints can not be applied with a QM/MM run, unless all of the MM atoms are frozen. Furthermore, the program will not check that the atoms of the MM region satisfy the imposed symmetry.