|ADIABATIC||The start structure for geometry optimization is given by the optimized structure of the previous scan step.|
|VERTICAL||The start structure for geometry optimization is given by the initial structure.|
|END=Real||End value for scanning coordinate. This specification is mandatory.|
|STEP=Integer||Number of scan steps. This specification is mandatory.|
OPTIMIZATION SCAN DX1 END=0.0 STEP=9 # GEOMETRY Z-MATRIX C N 1 R1 X 2 RCON 1 ACON H 2 R2 3 A1 1 DX1 # VARIABLES R1 1.18 R2 1.01 DX1 180.0 # CONSTANTS RCON 1.0 ACON 90.0 A1 90.0
If the keyword OPTIMIZATION had been omitted in the example, the variables R1 and R2 would be kept constant during the potential energy scan. If a Cartesian coordinate is scanned the syntax of the SCAN keyword changes to:
SCAN H4 END=(0.9,-0.4,-0.3) STEP=10
Here H4 denotes the atom that is moved during the potential energy scan. The END option now defines the final Cartesian coordinates of this atom. These coordinates are kept constant during the optimizations in the individual scan steps. Example on page of the tutorial discusses the input and output of a Cartesian potential energy surface scan in more detail.