Structure Optimizations Using Internal Coordinates

This is the default task of relax ($optimize internal on does not need to be specified!) You need as input the data groups :

$grad

cartesian coordinates and gradients as provided and accumulated in subsequent optimization cycles by the programs grad, or rdgrad etc.

$intdef

definitions of internal coordinates.

$redundant

definitions of redundant coordinates.

Output will be the updated coordinates on $coord and the updated force constant matrix on $forceapprox. If any non-default force constant update option has been chosen, relax increments its counting variables <numgeo>, <numpul> within command keyword $forceupdate. If the approximate force constant has been initialized ($forceinit on ) relax switches the initialization flag to $forceinit off. Refer also to the general documentation of TURBOMOLE. It is recommended to check correctness of your definition of internal coordinates:

1. Calculate their values for your cartesian start coordinates using the relax program (see Section 5.3.11) or within a define session.
2. Have a look at the eigenvectors of the BmB^†-matrix. Set some `?' behind keyword $intdef, if there are any eigenvalues close to zero ( < 10^-2 is to be considered bad for small molecules, but there is no general rule) check those internal coordinates for consistency which contribute to the corresponding eigenvector(s)!