Generate the Second Derivatives of the Energy in Internal Coordinates.

Modify input.dat.

intdif: (
derlvl = 1
 pos_disp = (
              (ni (p1 p2 ..... pn))
         )
)

where ni is an internal coordinate for which only a positive displacement is given, and p1 specifies the parity (+1 or -1) of coordinate 1 under the symmetry operation which generates the -ni displacement from the +ni displacement, p2 specifies the parity (+1 or -1) of coordinate 2 under the symmetry operation which generates the -ni displacement from the +ni displacement, etc. The number of vectors in the POS_DISP array should be equal to the number of internal coordinates for which only positive displacements are needed, and n should be equal to the number of symmetrized internal coordinates. This defaults to the zero vector.

Type intdif to generate the ider.dat file.