GEOMETRY
Step {Rad=MaxRadStep} {Angle=MaxAngleStep} {TrustRadius=MaxRadius}
..
END
Step
Controls that changes in geometry from one cycle to another are not too large:
MaxRadStep
Can only be used in combination with the old branch. An upper bound on changes in Cartesian coordinates or bond lengths, as the case may be. Default: 0.3 angstrom when optimization is carried out in internal coordinates, 0.15 angstrom for Cartesian optimizations.
MaxAngleStep
Can only be used in combination with the old branch.
Similarly this option limits changes in bond angles and dihedral
angles. Default: 10 degrees.
Input for MaxRadStep, MaxAngleStep is
in angstrom and degrees respectively, independently of the units used for
atomic coordinates input.
Note: Optimization of ring structures carried out in internal (z-matrix) coordinates is sometimes tricky due to the ill-defined last segment of the ring. When problems arise, try Cartesian optimization or consider using smaller limits on the steps (in particular the angles) so as to prevent the program from breaking the ring beyond repair.
MaxRadius
Can only be used in combination with the new branch. By default, the trust radius is set to 0.2. Using the key, the user can override this, setting a constant value. A conservative value is 0.2. A large system (eg 100 atoms) typically needs a larger trust radius (eg 0.8).
