34.2.16 Coordinate system (COORD)

COORD,type

This option chooses the coordinate system in which the optimization takes place. Default coordinate system is ZMAT. If the input coordinates are 3N cartesians and the Model Hessian is used in the optimization, the default is to use local normal coordinates. If you use cartesian coordinates, the program tries to fix rotations and translations, which might have occurred during the optimization step by rotating the new geometry to the frame of the previous one. This is also true if you used coordinates which are generated from cartesian coordinates (local normal coordinates and natural internal coordinates).

type may be

NORM

Optimization in local normal coordinates. This is default if the Model Hessian is used to approximate the hessian.

ZMAT

Use input coordinates; don't use local normal coordinates.

BMAT=filename

Use Pulay's ``natural internal coordinates''. Optionally you can write the created coordinates plus additional information about this optimization to a file.

CART or SYM

Optimization in 3N cartesian coordinates. Z-Matrix input coordinates will be destroyed on this entry. If numerical gradients or hessians are computed, the molecular symmetry will be used to shorten the number of energy and/or gradient calculations by computing only symmetry unique cartesian displacements.

3N or OPT3N

Optimization in 3N cartesian coordinates. Z-Matrix input coordinates will be destroyed on this entry. Symmetry will not be used in computing numerical gradients or hessians.

NOROT

Don't rotate cartesian coordinates.

The options BMAT, CART or SYM and 3N or OPT3N create 3N cartesian coordinates from any Z-matrix input, and allow optimizations in BMAT or Local Normal coordinates, even if the geometry input is given in Z-matrix form. Note that Z-matrix coordinates are destroyed and a new geometry record is generated.