Definition of Internal Coordinates

If structure optimizations are to be performed in the space of internal coordinates ($optimize internal, is the default setting), appropriate internal coordinate definitions have to be provided on data block $intdef. The types available and their definitions are described in Section 4.1.2. For recommendations about the choice of internal coordinates consult ref. [19]. Nevertheless the structure of $intdef will shortly be described. The syntax is (in free format):

 1   k   1.00000000   bend  1  2  3    val=1.9500  fdiag=.6666

The first items have been explained in Chapter 4.

Two additional items val=real, fdiag=real may be supplied for special purposes:

val=

serves for the input of values for internal coordinates for the interconversion internal → cartesian coordinates; it will be read in by relax if the flag for interconversion of coordinates has been activated ($interconversion on ), or by the interactive input program define within the geometry specification menu.

fdiag=

serves for the input of (diagonal) force constants for the individual internal coordinates to initialize $forceapprox.