52.7 Scaling of individual coordinates

SCALNM,options

The SCALE option of the SURF program enables a modifaction of the extension of all difference potentials by a common factor. In contrast to that the SCALNM directive allows for the scaling with respect to the individual normal coordinates. This is the recommended choice for potentials dominated by quartic rather than quadratic terms. At most 3N-6 individual scale factors and shift parameters can be provided. In particular the AUTO option was found to be very helpful in practical applications.

MODE=n

Denotes the normal coordinate to be scaled or shifted.

SFAC=value

Scaling factor for mode MODE. The default is 1.0.

SHIFT=n

Allows to shift the potential with respect to the specified coordinate by n or -n grid points, respectively. Default: SHIFT=0.

AUTO=on / off

AUTO=on switches on an automatic scaling procedure of the potential in order to determine meaningful elongations and SHIFT values with respect to all coordinates, i.e. for each normal mode an optimized scaling parameter SFAC and SHIFT parameter will be determined. Usually this results in an increased number of 1D grid points. The AUTO keyword intrinsically depends on the thresholds and parameters, which can be controlled by the keywords THRSHIFT, ITMAX, LEVMAX, DENSMAX, and DENSMIN.

ITMAX=n

Specifies the maximum number of iterations within the automatic scaling of the potentials (see Keyword AUTO).

THRSHIFT=value

Threshold controlling the automated shifting of potentials as obtained from the state densities on the lhs and rhs of the potentials. The default is given as THRSHIFT=0.05.

LEVMAX=n

Maximum number of vibrational states to be included for controlling the automated scaling and shifting procedure. The default is set to 5.

DENSMAX=value

Threshold for the maximum vibrational density on the edges of the potential needed for the automated upscaling of the potentials (see keyword AUTO).

DENSMIN=value

Threshold for the minimum vibrational density on the edges of the potential needed for the automated downscaling of the potentials (see keyword AUTO).